Najeeb Notes by SAQ (Final)

Najeeb notes by Saad Ahmed QudusiIndex: 0. Najeeb NMJ 1. Introduction to CNS 2. Sensory system and ascending tracts 3. Motor system and descending tracts 4. Medulla 5. Pons 6. Midbrain 7. Cerebellum 8. Diencephalon 9. Thalamus 10. Basal nuclei 11. Oculomotor nerve palsies 12. Blood supply to the brain 1|SAQ’s Najeeb notes Najeeb (Extra) Neuromuscular junction Video 1 Introduction: • Motor neurons come off the anterior horn of the spinal cord. • The nerve terminal (ending of the neuron) is connected to the muscle at the neuromuscular junction. The area of muscle at the neuromuscular junction is called the motor end plate. • Neurotransmitters are released from the presynaptic membrane (i.e. the nerve terminal) to transmit the impulse to the post synaptic membrane (i.e. the muscle membrane) The neurotransmitter machinery at the NMJ: • Within the neuron are membrane bound vesicles loaded with acetylcholine o The vesicles are synthesized in the cell body. These vesicles are made of special proteins. In fact, all the proteins in the nerve ending are synthesized in the cell body since there is no nucleus at the nerve endings. o The acetylcholine is synthesized at the nerve terminal. However, the enzymatic machinery concerned with ACh release and synthesis is synthesized in the cell body. • ACh synthesis o The nerve ending has choline transporters (special channels which transport choline inside the nerve ending from outside). o The acetate for ACh comes from the mitochondria already present in the nerve ending. o The enzyme needed for the synthesis of ACh from acetate and choline is called cholinacetyltransferase. • ACh loading o ACh is sequestered in the vesicles mentioned before via special channels in the vesicle membrane. The impulse: • The wave of depolarization approaches the nerve terminal leading to massive influx of Na+. 2|SAQ’s Najeeb notes • This wave of depolarisation activates depolarization sensitive calcium channels leading to calcium influx. • Calcium influx dependent exocytosis of ACh occurs. o The vesicles have special calcium sensitive proteins on its surface (synaptobrevin) and so does the membrane of the nerve terminal (syntaxin). o These protein channels are activated when calcium is bound to them and this allows both membranes (vesicular and nerve ending) to fuse and ACh is released. • The ACh now diffuses from presynaptic area to the postsynaptic area. • ACh gated cation channels (these are nicotinic channels) are present on the postsynaptic membrane. o These channels have to binding sites for ACh. As soon as ACh binds to these binding sites, the channels open o Sodium (cation) can now move in and Potassium (cation) can now move out. o However, since the resting membrane potential of -90 mV is nearer to the Potassium equilibrium potential, movement of potassium is not significant. Movement of sodium does occur however since -90 mV is far removed from sodium’s equilibrium potential • This potential produced by sodium influx is NOT called an action potential since it isn’t so. It’s called “end-plate potential” o Small fluctuations in the resting potential of post synaptic membrane are produced by a small release of ACh and these are called miniature end plate potentials. o The influx of sodium takes the resting membrane potential to threshold potential (if the ACh binding is strong enough) and voltage gated channels open, sodium influx starts and a new wave of depolarisation (action potential) ensues in the muscle • The ACh is degraded soon after the ACh has opened the sodium channels by acetylcholinesterase. o The acetate diffuses in blood and leaves o The choline is reabsorbed into the nerve cell via the choline transporters mentioned above. Video 2 • The ACh vesicles which had bound to the nerve membrane to release ACh are also recycled. o Proteins called clathrins pull the vesicle’s membrane inward and the whole vesicle pinches in, now without ACh. 3|SAQ’s Najeeb notes • CC (Patho): Myasthenia Gravis is an autoimmune disorder where the immune system makes antibodies against the ACh receptors on the muscle which competitively inhibit ACh binding. The miniature end plate potentials will be less in amount and it is very difficult to generate enough sodium influx to be able to depolarize muscle cell to threshold. o CC (Pharma): AChE inhibitors (physostigmine, neostigmine etc.) can be given in this condition so that ACh can accumulate in synaptic cleft which will be beneficial since the inhibition by antibodies is COMPETITIVE and can be countered by increasing ACh concentration. • CC (Patho): Eaton-lambert syndrome is a condition where antibodies are produced by the body against the presynaptic depolarisation sensitive calcium channels. o In myasthenia gravis, the person’s condition worsens with activity since accumulated ACh will be depleted but in ELS the person’s condition improves with activity since repeated action potentials arrive at nerve terminal leading to increased calcium release. • CC (Patho): Botulinum toxin is a proteolytic enzyme which is able to enter the cholinergic nerve ending (esp. at NMJs). o It cleaves synaptobrevin and syntaxin which were responsible for ACh release from vesicles into the synaptic cleft o Neuromuscular transmission ceases. The condition in babies is called floppy baby syndrome. • CC (Pharma): A toxin (tubercurare) binds to post synaptic ACh sensitive Na channels to prevent them from opening, effectively shutting down Neuromuscular transmission. o Sometimes this drug is used with anesthesia to allow the patient’s muscle to relax. • CC (Pharma): Succinyl choline is a drug which repeatedly stimulate the ACh sensitive postsynaptic Na channels. o This causes the fast sodium channels in the muscle to transition to inactive state. To regain their open state they must now transition to closed state first which can only happen in repolarized state. But since our drug above has the membrane constantly depolarised, this doesn’t happen and the fast sodium channels are effectively trapped in inactive state so even though membrane depolarises to threshold, the impulse is not transmitted as Na channels are inactive. 4|SAQ’s Najeeb notes Najeeb Neuro Video set 1-Introduction to Neuroanatomy Video 1: • Nervous system is concerned with receiving sensory input from the body, processing it (compare with previously stored information, storing it and concocting an appropriate response) and finally sending motor signals to effect the response Functional classification of the nervous system: • The nervous system is divided into CNS (brain and spinal cord) and PNS (Nerves) • PNS is further divided as follows: o Sensory PNS {some of these sensations go up to the consciousness level (you are aware of them) and others are those which do not go up to the consciousness level (e.g. BP, peristalsis etc.). The part of the nervous system responsible for consciousness is the cerebral cortex (all sensations that reach here go up to the conscious level)}.
Special sensations (sensations only received from certain specialized parts of the body) which include vision, olfaction, hearing, taste and sense of equilibrium (mainly from vestibular system)
General sensations • Somatic sensations (come from skin, locomotion system). They consist of touch, localized pain, temperature and proprioception (proprioception are all the sensations (esp. of position) that are received from the locomotor system). There are a lot of diseases which affect proprioception. • Visceral sensations (dull pain, distention) o Motor PNS {some of these are under your control (somatic motor responses) and others (e.g. persistalsis) are not (autonomic motor responses)}
Autonomic nervous system is further divided into: • Sympathetic nervous system (dominates under stress) • Parasympathetic nervous system (dominates under comfort) • Brain is divided into: o Forebrain (Prosencephalon)
Cerebral cortex (grey matter present on surface of the brain)
Superficially: Cerebral hemispheres (talencephalon)
Deep: Diencephalon o Midbrain (mesencephalon) o Hindbrain (Rhomboncephalon) 5|SAQ’s Najeeb notes o This crossing disrupts grey matter which breaks into small pieces and through these pieces white matter passes and this NETWORK of grey and white matter is called a reticular formation. o The larger fragments of grey matter are called nuclei too 6|SAQ’s Najeeb notes .
Pons
Medulla
Cerebellum Video 2 Structural classification of the nervous system: • Central Nervous system o Grey matter (collection of cell bodies of neurons within the CNS)
Cortex is the grey matter on the surface of CNS (e. • Those that connect right part of CNS with left part and vice versa are called ‘commissural fibers’.e. cerebral cortex)
Nuclei are collection of cell bodies deep within the CNS (pieces of grey matter surrounded by white matter). grey matter is in the centre (SCG=Sydney Cricket Ground=Spine Centre Grey) and white is in the outer region and vice versa for brain. towards brain and descending tracts take motor information caudally). • Hence as fibers ascend from spine to brain cross. since the white matter of brain needs to meet white matter of spinal cord. Reticular formations: • In spinal cord.g. From nuclei axons come out (for example nucleus of 3rd nerve is that which gives out axons which constitute the 3rd nerve) o White matter (collection of axons of neurons within the CNS)
Can be classified as: • Those that conduct impulses in the vertical axis of the body are called ‘tracts’ (ascending tracts take sensory information cephalically i. (corpus collossum is the largest commissure and it connects right cerebral hemisphere to left) • Those that connect anterior part of CNS with the posterior part are called ‘association fibers’ • The other type is neuroglial cells which can be considered the connective tissue around neurons. 7|SAQ’s Najeeb notes .Collection of axons outside the central nervous system is called a nerve: • So a collection of axons INSIDE CNS is called white matter whereas a collection of axons OUTSIDE CNS are nerves. • Another major difference between white matter and nerves is that nerves are insulated via Schwann cells whereas white matter is insulated via oligodendroglia. Basics of the Tracts: • Neuronal receptors are biological transducers (free nerve endings or cells associated with nerve endings) which can convert stimulus into electrical energy. What are associating fibres? • Association fibers are again white matter o They connect anterior part of CNS with the posterior part What are commissures? • Commissures. o For example rods and cones in the eyes convert visible light stimulus into electrical energy of the action potentials • Ascending tracts are groups of nerve fibers which transmit sensory information FROM receptors TO CNS. • The dorsal and ventral roots unite laterally to form the trunk of a spinal nerve which divides into anterior and posterior rami o The anterior (ventral) ramus innervates anterior and anterolateral parts of the body and contains both sensory and motor nerve fibers 8|SAQ’s Najeeb notes . o They connect lower part of CNS to upper part and vice versa. Najeeb Neurosciences Video set 6: Sensory system and ascending tracts Video 1 Introduction: What are tracts? • A group of neurons within the CNS with a common origin and destination moving vertically inside the CNS is called a tract o Tracts are all white matter since they’re bundle of axons. too. are white matter o They connect left CNS to right CNS. o Corpus collossum is the biggest commissure. • Descending tracts are groups of nerve fibers which transmit motor information FROM CNS TO receptors. • The anterior (ventral) horn of the spinal cord contains motor neurons whereas the posterior (dorsal) horn contains sensory neurons. hence. fine touch) The basics of the anterolateral system: • This system is responsible for primitive sensations like pain and itching. conduct very fast o Lateral funiculi or lateral columns (there are two) which contain both ascending and descending tracts
These are less heavily myelinated and. are purely sensory)
These are heavily myelinated and. The basics of the dorsal system: • This system is responsible for well developed sensations like proprioception (all sensations coming from locomotor system) • Information from this system is very accurately analysed by the CNS. • These tracts are not very organized and it is difficult to differentiate which part of the anterolateral system is receiving information from which part of the body. conduct very slowly o Anterior funiculi or anterior columns (there are two) which contain both ascending and descending tracts
These are less heavily myelinated and. o The anterolateral system has primitive sensations (e. • These tracts are well organized and it is easy to differentiate which part of the dorsal system is receiving information from which part of the body. you only get a rough idea of the location. if you are pricked with a needle (i. fine touch) you will be easily able to localize the exact position of the needle even if you aren’t looking at the are being pricked. o For example. hence. your body can’t localize crude touch if you’re not looking at the area being touched. 9|SAQ’s Najeeb notes . hence. hence. conduct very slowly • So essentially the anterior and lateral columns are grouped together very often and called the anterolateral system due to similar structural organization. • Information from this system is not very accurately analysed by the CNS. o The posterior (dorsal) ramus innervates posterior and posterolateral parts of the body and contains both sensory and motor nerve fibers • White matter of spinal cord is divided into: o Dorsal funiculi or dorsal columns (there are two) which contain only ascending tracts (and.g.g.e. crude touch) o The dorsal system has well developed sensations (e. o For example. 10 | S A Q ’ s N a j e e b n o t e s . o The medial bundle is called fasciculus gracilis and the lateral bundle is the fasciculus cuneatus. foot) end up medially in the spinal cord and then ascend. thigh and so on) start aligning laterally to those from the lower ones and then ascend. the more there are chances of loss of sensation in upper regions of the body and vice versa.e. • Receptors for the dorsal system: o Meissner’s receptors o Pacinian receptors o Muscle spindles o Golgi tendon organs • All of the neuronal fibers from these receptors enter via the dorsal root ganglion of the spinal cord. o So if you make a section from the lower part of the spinal cord you will find only fasciculus gracilis as the bundles from the upper part of the body have not been added yet and if you make a section from the upper part you will find both. leg. o So the fibers from the lowest region would be the most medial and the fibers from the highest region of the body would be the most lateral in position o And these move ipsilaterally (right bundles from right side of the body and left from left) • The above means that the more lateral the lesion in the dorsal column. Video 2 • In the brain stem. o The fibers from the subsequent upper regions (i.The dorsal system of tracts: • Recall that the dorsal system has ONLY ascending (sensory) tracts. o These neurons are called first order neurons since these are the first in the chain of the sensory system • Visualise this: o The fibers from the lower regions (e. collections of cell bodies are called nuclei • The two fasciculus gracilis (first order neurons) terminate in the two nucleus gracilis in the medulla oblongata of the brain • The two fasciculus cuneatus (first order neurons) terminate in the two nucleus cuneatus in the medulla oblongata of the brain • The neurons in the nucleus gracilis and cuneatus are called second order neurons • The second order neurons cross the midline to go to the opposite side.g. o The posterolateral part is further divided into dorsal and ventral. It is here that the medial lemnisci reach and second order neurons terminate. o These are called the medial lemniscus systems. posterolateral and posteromedial parts. • The fibers (third order neurons) from ventroposterolateral nucleus of ventral posterolateral thalamus enter posterior limb of internal capsule and fan out superiorly to reach the cerebral cortex (this fanning is called corona radiata). right and left medial lemniscus systems) • Terminology: o If a lot of axons make a circular bundle. o These are called internal arcuate fibers (the crossed fibers that is). • The thalamus lies in the middle and lateral to it on both ends lie one internal capsule each lateral to which on each side lie one nucleus each. The third order neurons start from here • Ventroposteromedial receives sensation from head and neck. (one on each side. • The thalamus has anterior. it is called a lemniscus (as before) • These medial lemnisci then ascend towards upper medulla. • Thermal sensory pathway follows similar anatomical course as the pain sensations pathway 11 | S A Q ’ s N a j e e b n o t e s . The ventral part has three nuclei:
Ventroanterior nucleus
Ventrointermediate nucleus
Ventroposterior nucleus (further divided into ventroposterolateral and ventroposteromedial) • Ventroposterolateral nucleus receives sensations from most of the body. The pain and temperature pathway: • Receptors for pain are free nerve endings whereas the receptor for temperature are thermal receptors. • The area where these third order neurons terminate in the postcentral gyrus (sensory cortex) Video 3 The Anterolateral system of tracts: 1. right bundle of second order neurons are linked to left side of body and vice versa. it is called a fasciculus (as before) o If a lot of axons make a flattened bundle. pons and midbrain and eventually reach the thalamus. o Hence. Crude touch pathway: • The first order neurons follow the same path as the first order of pain and temperature. o This lateral spinothalamic tract is. they give off ascending and descending branches inside the spinal cord. the fibers are added MEDIALLY. recall. These branches as a whole are called the dorsolateral tract of lissaure. potassium ion and PGE2. o The fibers of the second order neurons cross to the contralateral side o These second order fibers will go up to the thalamus and hence. too. thermal and chemical stimuli of pain
One first order neuron may pair up with more than one second order neuron making it difficult to localize (and hence. bradykinin. 12 | S A Q ’ s N a j e e b n o t e s . • The first order neurons have their cell bodies in the dorsal root ganglion o The first order fibers terminate in the dorsal grey horn of spinal cord in an area called substantia gelatinosa. dull) pain. o Before terminating. however. these are collectively called the lateral spinothalamic tract. • Fibers are divided according to degree of myelination as follows: o Type A delta fibers are heavily myelinated o Type B fibers are less heavily myelinated o Type C fibers are not myelinated at all 1A. o It is these branches that connect with the second order neurons • The second order neurons start within the spinal cord in the substantia gelatinosa and their cell bodies. unlike dorsal system which basically means that fibers from the hand will lie medial to the fibers of the foot. concerned with pain and temperature o As we ascend. Acids. histamine. • Chemical mediators of pain are 5HT. 2. lie in this region unlike the dorsal system. The pain sensation pathway: • Pain sensations are sent via two pathways o Sharp pain (pin prick) is carried via type A delta fibers
Fast transmission
Sense mechanical and thermal stimuli of pain
Each first order neuron pairs up with one second order allowing for localization of pain o Dull pain is carried via type C fibers
Slow transmission
Sense mechanical. on their way up the brain stem. o Some pain fibers also end up in the singulate gyrus which is associated with the emotional responses to pain. The spinotectal pathway: • Goes from spine to the tectum of mid brain • Concerned with spinovisual reflexes. do not go to the contralateral side. o Some pain fibers (esp. (e. The above three pathways fuse together in the medulla: • Then onwards they run as a single bundle which is called spinal lemniscus which will now ascend all the way to thalamus from the medulla where they collected together. severity etc.g.) Side note: Often times fibers of other senses give off collateral connections to pain fibers and if these are stimulated. 4. 13 | S A Q ’ s N a j e e b n o t e s . • The second order neurons. that the medial lemniscus was coming from the dorsal columns o The spinal lemniscus connects with the ventroposterolateral nucleus of the thalamus
The sharp pain fibers end in the VPL nucleus and so do some of the dull pain ones
The rest of the dull pain fibers end up in the intralaminal nuclei of the thalamus and. Rather they go to the anterior column of white matter of spinal cord and then ascend and are thus called anterior spinothalamic tract. give fibers to the reticular formations. they can significantly inhibit the pain fibers. it would result in a decrease in pain) Video 4 An Analgesia system in the body: • Throughout the CNS at various positions are certain nuclei which give off certain descending neurons. if you massage the skin. • Reticular formation is responsible to keep the cortex “awake”. dull pain fibers) also end up in the insular cortex associated with autonomic responses to the pain o MOST of the pain fibers end up in post central gyrus and are associated with analysis of the pain (localisation. however. 3. o Recall here. Three minor ascending tracts: 1. end up in the cerebellum
The cell bodies make a vertical nucleus called the dorsolateral nucleus of clark which extends from C8-L3 (This nucleus receives information from the lower part of the body)
However there are second order neurons till S3 and. hence. • This pathway is called the cuneocerebellar pathway • Anterior spinocerebellar tract: o The second order neurons cross to the contralateral side in this case and then ascend to superior cerebellar pudencle to end up in cerebellum o After that they turn again to recross and finally end in the original part of the cerebellum they should have ended up in. From right goes to right cerebellum and info. there is another nucleus (accessory cuneate nucleus) which receives information from upper part of the body. move to ipsilateral white matter and ascend
Cell bodies lie in the grey matter
They ascend and. Spino-olival pathway: • First order end in grey matter • Second order cross to contralateral side 14 | S A Q ’ s N a j e e b n o t e s . From left goes to left cerebellum) • Dorsal spinocerebellar tract: o The first order neurons terminate in the grey matter
Cell bodies lie in the dorsal root ganglion o The second order neurons. o These have the capability of inhibiting the pain sensations via release of morphine-like substances called endorphins and enkephalins. these (L4-S3) ascend to connect with the clark’s nucleus
Above C8. Spinotectal pathway: • First order end in grey matter • Second order cross to contralateral side o Ascend all the way to tectum 2. Spinocerebellar pathways: • These are ipsilateral pathways (info. via the inferior cerebellar pudencle. doesn’t have direct connections to the muscle and stimulates neurons in the primary motor cortex first which then stimulates the required muscles Video 2 The Corticospinal tract: • Cell bodies of the first order neurons are present in the cortex 15 | S A Q ’ s N a j e e b n o t e s . o It doesn’t have a direct connection to the muscles rather it stimulates neurons in the primary motor cortex which then stimulate the muscles o Broca’s area is concerned with speech (phonation) o Frontal eye field is concerened with eye movements (this is superior to broca’s) o Above that is the neck area o Above that is an area concerned with planning skilled hand movements • Superior to the precentral gyrus is another region called the supplementary motor area. too. o Ascend all the way to olive • Third order then go to cerebellum via inferior pudencle 3. o Concerned with “planning” the motor activities o Receives proprioceptive information from the body. analyzes the action that is to be performed and then sends out the required stimulatory information to primary motor cortex. Spinoreticular fibers: • Fibers don’t cross and ascend all the way to reticular formation Najeeb Neurosciences Video Set 7.Motor system and descending tracts Video 1 Motor cortex: • The highest centre responsible for voluntary activity • Lies anterior to the central sulcus of the brain o Recall that the sensory centres were posterior to the central sulcus • Precentral gyrus lies immediately anterior to the central sulcus o This area is called the primary motor cortex • Anterior to the precentral gyrus is another region called the premotor area. o Concerned with primitive movements like movements of the hip and the trunk and these are usually bilateral o Similar to the precentral gyrus. it. ofcourse. however. o Some of these. • White matter columns in the mid brain connect the brain stem with the cerebral cortex (these areas (there are 5) are called crus cerebri) o These are. o 30% from the premotor + supplementary motor area o 40% of the fibers come from the sensory cortex o All of these cell bodies lie in the 5th lamina of the cerebral cortex • All of the fibers converge at a point in the internal capsule. These cell bodies are called cell of Batz often equivalent to the size of 8 RBCs. These are concerned with more developed movements. unlike other neurons which connect with internuntial neurons first. These are the fibers that are. coming from the supplementary motor cortex • Some important connections made by the descending fibers: o Initially they make collateral connections within the cerebral cortex for coordination. The fibers from these cells are heavily myelinated. quite rightly. coming from the premotor cortex. o 30% from the primary motor area
Some of the neurons here are very big. These are the fibers that are. This results in hemiplagia causing a lot of function to be lost since a lot of fibers were bundled together and now all of these are affected. o Inferior to that. called corona radiate (the fanning structure that is) • Thereafter they continue downwards in a very compact (bundled together) manner o Often times the arterial supply to this area (lenticulostriate artery) gets blocked in old age. o They fan into this point from all the points in the cortex and are. most of them cross to the contralateral side (called the major motor crossing). of course. our original descending fibers which were descending from the internal capsule • These columns proceed to the pons where they are dispersed o Over here there are also other fibers coming from cortex and connecting with the pons in the pontine nuclei called the corticopontine fibers • The columns are dispersed over the pontine nuclei and descend to form the pyramids of the medulla o Hence. These are concerned with more primitive movements. they make lenticular connections in the basal ganglia 16 | S A Q ’ s N a j e e b n o t e s . corticospinal tracts are also called pyramidal tracts in this region. o In the pyramids. These are then called the lateral corticospinal tracts and move in the lateral white column of the spinal cord. These are then called anterior corticospinal tracts and move in the anterior white column of the spinal cord. These directly stimulate the lower motor neurons. continue without crossing. ofcourse. they also make connections with the olives in the medulla Video 3 Upper motor neurons and lower motor neurons: • Lower motor neurons are those that come out of the CNS and make neuromuscular junctions.
Vestibulospinal tract from pontomedullary junction to LMN. o Inferior to that.
Corticospinal tract
Corticonuclear tract (Those connected with nucleus in medulla are called corticobulbar fibers) o Others have a subcortical origin
Tectospinal tract (the superior coliculus of the tectum is concerned with visual reflexes while the inferior coliculus is concerned with visual reflexes)
Ruberospinal tract from the red nucleus to the lower motor neurons
Reticulospinal tract from reticular formation to LMN.g. o Some of these have a cortical origin. o Inferior to that.
Olivospinal tract from olives to LMN Side note: Descending tracts are classified as pyramidal tracts (those that pass through the pyramids e. corticospinal tract and corticonuclear tracts) and extrapyramidal tracts (all of the subcortical origin) Functional implications: • Muscles of the body are classified as flexor muscles and extensor muscles o Extensor muscles serve to support and move the body against gravity e. • Upper motor neurons are all those which originate from higher centres and connect with the lower motor neurons to affect their activity. they make connections with the reticular formations which are responsible for stimulating the cerebral cortex. when standing up o Flexor muscles serve the opposite function 17 | S A Q ’ s N a j e e b n o t e s . they make connections with the vestibular nuclei (I believe this was at the pontomedullary junction or somewhere around there) o Inferior to that. they make connections with the red nuclei in the mid brain o Inferior to that.g. Reticular formation: • Reticular formation extends throughout the brainstem. o Descending reticular formation 18 | S A Q ’ s N a j e e b n o t e s .S4) o Originates from anterior group of neurons of the hypothalamus Najeeb neurosciences video set 11-Medulla Video 1 • Medulla is the lower part of the brain stem (midbrain.7. • We’ll divide the medulla intro ascending systems (sensory). It is further divided into o Ascending reticular formation which connects with the intralaminar nuclei of the thalamus and then continues towards the cerebral cortex.9 and 10 and S2. • It extends from the pontomedullary sulcus to the pyramidal decussation • It has two medial swellings (pyramids) and two lateral swellings (olives) and from medulla. extend also. • Parasympathetic pathway is craniosacral pathway (from cranial nerves 3. pons and medulla) and is part of the rhomboncephalon (hind brain (cerebellum. Sweating function of half of the face is gone. the inferior cerebellar pudencles. posterior (cerebellar) connections and anterolateral connections (cranial nerves). ptosis occurs and the pupils are constricted. descending systems (motor). pons and medulla)). It serves to keep the cerebral cortex active maintaining a state of wakefulness. • Certain tracts serve to enhance the tone of extensor muscles o Vestibulospinal tracts (major player) o Pontine reticular nuclei from the reticular formation (accessory player) • Certain tracts serve to enhance the tone of flexor muscles o Ruberospinal tracts (major player) o Medullary tracts Sympathetic and parasympathetic pathways: • Sympathetic pathway is thoraco lumbar pathway (T1-L2) o Originates from posterior group of neurons of the hypothalamus o Some fibers from T1 and T2 ascend to supply the head and neck
CC: Horner’s syndrome is a condition where the ascending T1 and T2 fibers are blocked.S3. • Also ascending from the spinal cord. After connecting with the nuclei. o Following this crossing. o Following these nuclei. • Reticular formation has the following centres in the medulla: o Cardiac centre o Vasomotor centre o Respiratory centre o Gastrointestinal centre
Area postrema is a break in the blood brain barrier through which the neurons in this region can sample substances in the blood. the cochlear fibers cross and ascend in what is known as the lateral lemniscus. • It can stimulate chemoreceptor trigger zone if it finds toxic substances. the fasciculi. lateral ascending and spinotectal pathways o These would unite in the spinal lemniscus in the medulla and ascend further Side note-lateral lemniscus: At the pontomedullary junction. the internal arcuate fibers and finally. a crossing of the second order neurons occurs to the contralateral site (the axons of these neurons are called internal arcuate fibers). the nuclei. are the anterior ascending. lie the dorsal and ventral cochlear nuclei which receive sensations from the cochlear fibers of the vestibulocochlear nerve. Descending structures of the medulla: • The medially situated pyramids contain the corticospinal (upper motor neurons) tract which descend to the spinal cord 19 | S A Q ’ s N a j e e b n o t e s . the medial lemniscus. • CTZ can stimulate gastrointestinal centre to cause reverse peristalsis and cause nausea Video 2 Internal structure of the medulla: Ascending structures: • Fasciculus gracillis and fasciculus cuneatus from the dorsal column ascend to connect with the gracillis nucleus and cuneate nucleus respectively. they continue ascending as the medial lemniscus o So from inferior to superior in the medulla (for the dorsal column of the spinal cord) you find.
They do eventually cross at the level of the body that they supply Video 3 Posterior connections of the medulla: • Medulla is connected to the cerebellum via the inferior cerebellar pudencle.
Once connected. o Some (10%) do not cross at the pyramidal decussation and constitute the anterior corticospinal tract. eventually terminating at the same side of the body as their site of origin. • Three types of fibers ascend from spinal cord to medulla and then move posteriorly to connect with the cerebellum o Cuneocerebellar fibers which carry sensory input from upper limb going from accessory cuneate nucleus to the cerebellum via the inferior cerebellar pudencle o Dorsal spinocerebellar fibers which carry sensory input from the ipsilateral lower limb and go to medulla then cerebellum via the inferior cerebellar pudencle without connecting to the accessory cuneate nucleus o Ventral spinocerebellar fibers which carry sensory input from the contralateral lower limb since they cross as soon as they enter the spinal cord
They DON’T exit through the inferior cerebellar pudencle and keep ascending upto midbrain. • Olivocerebellar fibers go to the contralateral side of cerebellum from the olives in the medulla via inferior cerebellar pudencle. move out of cerebellum and cross to contralateral side again. they again.
They connect to cerebellum via the superior cerebellar pudencle of the midbrain. o Most (90%) of these have crossed to the contralateral side in what is known as the pyramidal decussation and constitute the lateral corticospinal tract. o The olives receive fibers from the red nuclei and hence this entire pathway is called ruberolivocerebellar pathway • Also present in the medulla are arcuate nuclei o Arcuate nuclei receive fibers from the cerebral cortex o After connecting with the arcuate nuclei these fibers connect with the cerebellum via the inferior cerebellar pudencle and this pathway is called arcuatocerebellar pathway • Reticulocerebellar pathway o Fibers going from the medullary path of reticular formation to the cerebellum 20 | S A Q ’ s N a j e e b n o t e s . Side note-Central tegmental pathway: This is a bundle of white matter within the central part of the brain stem. Also many fibers from reticular formation pass through this pathway on their way to the thalamus. This supplies the vagus nerve with branchiomotor fibers for the larynx pharynx and soft palate. • Nuclei: o The hypoglossal nerve (12th cranial nerve) receives fibers from the posteromedially placed hypoglossal nucleus o The vagus nerve (10th cranial nerve) receives fibers from the following
Dorsal nucleus of vagus nerve. The ruberolivary fibers pass through this pathway.
Spinal nucleus of the trigeminal system Video 4 o The 9th nerve receives fibers from the following
Branchiomotor fibers from the nucleus ambiguous
Spinal nucleus of the trigeminal nuclear system
Nucleus of the tectus solitarius o The 11th nerve receives fibers from the nucleus ambiguous • Other nuclei which lie in the medulla o Lower part of vestibular nuclei o Inferior cochlear nuclei 21 | S A Q ’ s N a j e e b n o t e s . This lies lateral to the dorsal nucleus of vagus nerve
Nucleus ambiguous which lies anterior to the three nuclei already mentioned. Fibers from the nucleus of tectus solitarius also pass through this path way on its way to the ventroposteromedial nucleus of the thalamus. Anterolateral connections: • From the medulla exit o Fibers of 12th cranial nerve in the preolivary sulcus which lies between pyramid and olive o Fibers of 9th nerve (superiorly) in the post olivary sulcus (between olive and inferior cerebellar pudencle) o Fibers of 10th nerve (in the middle) in the post olivary sulcus o Fibers of the cranial part of 11th nerve (inferiorly) in the post olivary sulcus. This gives off parasympathetic fibers and lies lateral to the hypoglossal nucleus
Nucleus of tectus solitarius which gives off taste (lateral part) and visceral sensory fibers (medial part). the internal arcuate fibers) o At this level you will also find the uncrossed corticospinal tracts in the pyramids o At this level you will also find nucleus ambiguous o At this level you will also find hypoglossal nuclei o At this level you will also find inferior olivary nuclei o At this level you will also find the medial longitudinal fasciculus o At this level you will also find ventral spinocerebellar and dorsal spinocerebellar tract o At this level you will also find the lateral spinothalamic tract (spinal lemniscus) o At this level you will also find spinal nucleus of the trigeminal system • Now we ascend superiorly upto the superiormost part of medulla o At this level you will also find uncrossed corticospinal fibers o At this level you will also find inferior olivary nuclei o At this level you will also find the hypoglossal nuclei o At this level you will also find dorsal nucleus of vagus o At this level you will also find nucleus tectus solitarius o At this level you will also find nucleus ambiguous o At this level you will also find inferior part of vestibular nuclei o At this level you will also find inferior cochlear nuclei o At this level you will also find spinal nucleus of the trigeminal system o At this level you will also find medial longitudinal fasciculus 22 | S A Q ’ s N a j e e b n o t e s .Medial longitudinal fasciculus: • Present throughout the brain stem • Connects with the nuclei of the cranial nerves allowing intercommunication between the nuclei. you will be at the level of the pyramidal decussation o At this level you will also find the nucleus gracillis and cuneatus o At this level you will also find ventral spinocerebellar and dorsal spinocerebellar tract o At this level you will also find the lateral spinothalamic tract (spinal lemniscus) o At this level you will also find the medial longitudinal fasciculus o At this level you will also find spinal part of accessory nerve o At this level you will also find spinal nucleus of the trigeminal system • If you move superiorly for a while.e. Review: • If you take an inferior section of the medulla. you will soon be at the level of the major sensory decussation (i. • Pons is also part of the hindbrain (cerebellum. o Cerebellum lies on the posterior aspect of the pons o The middle cerebellar peduncle covers part of the inferior cerebellar peduncle as well as part of the superior cerebellar peduncle • Pons is associated with the 5th. 6th. o This cavity is expanded posteriorly in the region of their union (at the level of pons. 7th and 8th cranial nerves exit from the pontomedullary sulcus. o The spinal canal ascends and the cerebral aqueduct descends to unite. corticopontocerebellar pathway. These fibers are called pontocerebellar fibers. medulla and pons) • Pons is connected to the cerebellum via the middle cerebellar peduncle. medulla and cerebellum) • This expanded cavity is called the fourth ventricle (remember that the main cavity in the inferior part of the medulla was the central canal whereas the main cavity in the superior part of the medulla was the floor of the fourth ventricle). o At this level you will also find the lateral spinothalamic tract (spinal lemniscus) Najeeb neurosciences video set 12-Pons Video 1 Introduction: • Pons lies in the brain stem above the medulla and below the midbrain. The fourth ventricle: • A CSF filled cavity lies in the upper parts of the brain called the cerebral aqueduct • Another CSF filled cavity lies in the central part of the spinal cord and is called the spinal canal. another set of fibers exit via the contralateral (they cross) cerebellar peduncles to enter the two cerebellar hemispheres on either side of the pons. • Najeeb trivia time-Pons means bridge: o A lot of fibers come from all lobes of the cerebral cortex to terminate in the pontine nuclei. 7th and 8th cranial nerves o The 5th nerve comes out of the anterolateral aspect of mid pons o The 6th. These fibers are called corticopontine fibers o From the pontine nuclei. o The floor of the fourth ventricle lies in the brain stem and the roof of the fourth ventricle lies in the cerebellum 23 | S A Q ’ s N a j e e b n o t e s . o The entire pathway is thus called. o The swelling is produced by the internal genu of the 7th nerve o The 7th nerve fibers project posteriorly from the 7th nucleus before turning and exiting anteriorly. if you may. o This “u-turn” of the fibers makes the internal genu of the 7th nerve and it is this genu that makes the longitudinal elevations appear swollen. • On the lateral sides of the longitudinal elevations are longitudinal depressions called the sulcus limitans. Video 2 24 | S A Q ’ s N a j e e b n o t e s . lies the upper part of the floor of the fourth ventricle Posterior aspect of the pons: • Remember that the cerebellum lies on the posterior aspect of pons. • There is a longitudinal depression in the floor of the fourth ventricle called the median sulcus • On the sides of the median sulcus. o The swellings (one on either side of the median sulcus) are called facial coliculi since the 7th nerve is the facial nerve. the fibers go posteriorly and arc around the nucleus of 6th nerve to take a “u-turn”. o To do the above. the vestibular and cochlear nuclei lie lateral to the sulcus limitans. o So between the median sulcus in the middle and the sulcus limitans on the sides lie the longitudinal elevations. o The vestibular nuclei lie at the pontomedullary junction o This lateral area of the fourth ventricle is the vestibular area. o These neurons supply noradrenergic fibers to the CNS o This group of neurons is called the locus cerulius • Since the 8th nerve (vestibulocochlear nerve) lies lateral to the 7th nerve. • This depression elevation and then depression sequence is called the median eminence o On the superior aspect of the median eminence lies the substantia ferrugenia which contains cell body of highly pigmented neurons. • The floor of the fourth ventricle is diamond shaped when viewed from the posterior. o So in the posterior aspect of pons. there is a longitudinal elevation which becomes swollen as it descends. the fibers would go as the inferior brachium and terminate in the medial geniculate bodies o From here the fibers would continue as auditory radiation and terminate in the temporal lobe of the cerebral cortex. lower level): • In the front of the pons. There are nuclei as well in the trapezoid body called the trapezoid nucleus o The fibers from the trapezoid body would ascend as the lateral lemniscus and terminate into inferior colliculus of the midbrain. • The anterior part of the internal structure is called the base of the pons whereas the posterior part of the internal structure is called the tegmentum o The demarcation between anterior and posterior is made via the trapezoid body (crisscross fibers) • The internal ear has cochlea (associated with hearing) and vestibular apparatus (associated with sense of balance) o These give off the cochlear and vestibular components of vestibulocohlear nerve respectively. Some fibers. would terminate in the superior olivary nucleus and then continue towards the inferior colliculus o From the inferior colliculus. there are dorsal cochlear nuclei and ventral cochlear nuclei o From ventral cochlear nuclei many fibers go contralaterally.e. The base of the pons: THE DESCENDING TRACTS: • The base contains pontine nuclei o These nuclei receive the corticopontine fibers mentioned earlier o These then give off pontocerebellar fibers which move contralaterally to the middle cerebellar peduncle mentioned earlier • The corticonuclear as well as corticospinal fibers also pass through the pons on their way to nuclei and spine respectively THE ASCENDING TRACTS: 25 | S A Q ’ s N a j e e b n o t e s . There may be some contribution from dorsal nuclei to this crisscross. A section of pons near the inferior pontine sulcus (i. on their way as the lateral lemniscus. the basilar artery lies in the basilar groove. • In pons. • The pons lies between the inferior and superior pontine sulci. It is these crisscross fibers that make the trapezoid body. o These are taste fibers for the anterior two thirds of the tongue • Another nucleus (medial to tractus solitarius) provides parasympathetic fibers to CN VII. These fibers are for facial expression. pain and temperature from ear and terminate in the spinal nucleus of trigeminal system. superior salivatory nucleus/lacrimatory nucleus and also receives fibers which convey touch. • The medial lemniscus (crossed fibers from the cuneate nucleus and the gracille nucleus in the medulla) goes through pons on its way to the ventroposterolateral nucleus of thalamus. o This is where the nucleus of 6th nerve is present o This is also where the CN VII fibers arc around nucleus VI. tractus solitarius. THE LOCAL SYSTEM OF THE PONS: • There are two depressions on the base of the fourth ventricle called the facial colliculi. • So in essence CN VII receives fibers from motor nucleus of facial nerve. • The lateral lemniscus (from trapezoid bodies) lies lateral to the spinal lemniscus on cross sections. o Some of these fibers aggregate in teregopalatine (something like that) ganglion and go to lacrimal glands o Others aggregate in the submandibular ganglion and go to salivary glands. • The ventral spinocerebellar tract can also be seen on cross sections of the pons on its way to the superior cerebellar peduncle. • The trigeminal system has four nuclei o The spinal nucleus which lies in all of medulla and lower pons o The principal nucleus which lies in mid pons o The mesencephalic nucleus which lies in midbrain mainly o Motor nucleus of trigeminal nerve which lies medial to the principal nucleus • The vestibulocochlear nuclei lie laterally in pons o There are two dorsal and two ventral cochlear nuclei o There are two vestibular nuclei o The vestibular nucleus is split into four parts
All of the superior and most of the medial and lateral parts of the vestibular nuclei lie in pons 26 | S A Q ’ s N a j e e b n o t e s . • The spinal lemniscus (anterolateral spinothalamic tracts along with spinotectal fibers) also moves through pons on its way to the ventroposterolateral nucleus of thalamus and lies lateral to the medial lemniscus on cross sections. o The nucleus of the 7th nerve is more anterior and more lateral to the 6th nerve • Nucleus of tractus solitarius also contributes fibers to CN VII. on the posterior aspect of the midbrain. each half is called a cerebral peduncle since these halves connect the rest of the CNS to the cerebrum Cross section of the midbrain: • On cross sections. central canal for spinal cord.g. in essence the following are the cavities across the CNS. hence. if you move your eyes to the right. o To facilitate these coordinated movements. o This medial longitudinal fasciculus also courses throughout most of the brain stem and. cerebral aqueduct can be seen o So. Najeeb neurosciences video set 13-Midbrain Video 1 The midbrain: • There are two longitudinal elevations on the sides and in the middle. substantia nigra can be seen • On cross sections. lower part of the fourth ventricle for the medulla. right eye moves laterally and left eye moves medially o There are separate muscles for lateral and medial movement of eyes innervated by separate cranial nerves (one by 6 and other by 3). the medial longitudinal fasciculus is required so that the cranial nuclei can communicate and coordinate. upper part of the 27 | S A Q ’ s N a j e e b n o t e s . on the anterior aspect of midbrain.
The inferior part of the vestibular nuclei lies in the upper medulla • The medial longitudinal fasciculus is responsible for intercommunication and coordination between the cranial nerve nuclei o E. the area is called interpeduncular fossa o The two longitudinal elevations are called crus cerebri • There are two swellings on each side on the posterior aspect of the midbrain called colliculi (one superior and one inferior colliculus on either side) o The superior colliculi are related to the visual system o The inferior colliculi are related to the auditory system • If we cut across the midbrain so as to cut it into right and left halves. Najeeb seems awefully quiet for the next 7 mins so I’ll just stop here. throughout the pons o CC: medial longitudinal fasciculus syndrome can render the medial longitudinal fasciculus ineffective due to damage leading to poor coordination in cranial nerve motor functions. • Substantia nigra is divided into two parts o The posterior part is called pars compacta and has densely packed neurons o The anterior part is called pars reticularis and has less densely packed neurons o Substantia nigra has neurons connected to caudatum putamen (something like that). fourth ventricle for the pons. There is hypokinesia (difficulty in initiating movement). Crus cerebri anteriorly. tegmentum posterior to that. These neurons have dopaminergic receptors at the nerve endings and they are called striatum. the superior colliculi are concerned with visuospinal reflexes whereas the inferior colliculi are concerned with auditospinal reflexes • Fibers from the superior and inferior colliculi descend into the spine to mediate these reflexes (e. Cross section at the level of inferior colliculus: • To put things into perspective. crus cerebrum. on their way to the inferiorly situated pontine nuclei pass through the crus cerebri. There is rigidity and also tremors with loss of postural reflexes
CC: certain drugs can also block this pathway (anti-dopaminergic pathway) • Crus cerebri lie anterior to the substantia nigra o The corticopontine fibers. These lie on either side of the corticospinal fibers. on their way to the various cranial nerve nuclei. cerebral aqueduct posterior to that and finally the tectum being the most posterior. This pathway is called nigrostriatal pathway
CC: Parkinson’s disease is a condition in which the nigrostriatal pathway is damaged. These descend alongside the corticopontine fibers 28 | S A Q ’ s N a j e e b n o t e s . the cerebral aqueduct for the midbrain and finally the diencephalon has a cavity called the third ventricle o All the above cavities are filled with cerebrospinal fluid (CSF) • Structures posterior to the cerebral aqueduct are called the tectum • Structures anterior to the substantia nigra are called the crus cerebri o This part is also called the base of the midbrain • Structures between the cerebral aqueduct and the substantia nigra are the tegmentum • So each cerebral peduncle contains. o The corticonuclear fibers. you moving to the side as soon as you hear a horn honking right behind you).g. pass through crus cerebri. These fibers are called tectospinal fibers. substantia nigra posterior to that. tegmentum and then tectum The tectum: • As mentioned earlier. the inferior colliculi receive fibers carrying sensations from both ears (mostly the contralateral ear but some fibers from the ipsilateral ear as well) o From the inferior colliculi. on their way to synapse with the lower motor neurons. fibers would carry the auditory sensation to the auditory part of the cortex • The tegmentum at this level contains the ascending sensory fibers o Fibers from the dentate nuclei (one on each side) of the cerebellum pass through the tegmentum of the inferior part of the mid brain to synapse in the red nucleus which is situated in the tegmentum of the superior part of the mid brain. o The corticospinal fibers. o From the medial geniculate body. hence. pass through crus cerebri. you will see the lateral lemnisci approaching the inferior colliculi on the posterior aspect of the cerebral aqueduct (see below) o Auditory fibers (cochlear part of the vestibulocochlear nerve) from the ear go to the cochlear nuclei residing in the pons and medulla o From the cochlear nuclei. This is the only cranial nerve that exits through the back of the CNS o The medial longitudinal fasciculus lies anterior to the periaqueductal grey matter o The nucleus raphae and central tegmental nuclei can also be found around the periaqueductal grey matter. o This pathway is called dentoruberothalamic pathway since fibers from the red nucleus would also go up and synapse in the thalamus o The dentorubero fibers cross in the tegmentum of the inferior part of midbrain o The second ascending system is the medial lemniscus (dorsal spinal column) and this lies lateral to the dentorubero fibers 29 | S A Q ’ s N a j e e b n o t e s . These lie between two tracts of corticopontine fibers o SIDE NOTE: throughout the CNS. motor (descending) fibers would lie anteriorly whereas the sensory (ascending) fibers would lie posteriorly. • Periaqueductal grey matter is grey matter that surrounds the cerebral aqueduct o The nucleus of the fourth nerve lies on either side of the periaqueductal grey matter in the tegmentum at the level of the inferior colliculus. the fibers would come out and cross (most of them) in the trapezoid body o The fibers (both crossed and uncrossed) ascend as the lateral lemniscus o The fibers in the lateral lemniscus synapse in the nuclei inferior colliculi and. fibers (collectively called the inferior brachium) carry auditory information to the medial geniculate body of the thalamus
From each inferior colliculus. commissural fibers also come out to connect with the contralateral inferior colliculus.
These nuclei have descending fibers and they release enkephalins and serotonin to inhibit pain transmission at the point of entry of the anterolateral ascending system of spinal cord • At this level. 30 | S A Q ’ s N a j e e b n o t e s . • The locus cerulius (discussed in pons) can also be found at inferior colliculi level • The interpeduncular nucleus lies just anterior to the substantia nigra and right in the between the two peduncles and plays a part in hunger • Reticular formation is present at all levels of midbrain Cross section at the level of superior colliculi: • As before. in the center of the tegmentum is the central tegmental tract
It carries reticulothalamic fibers (ascending) connecting the reticular formation with the thalamus
It also carries the rubero-olivary fibers (descending) connecting the red nucleus with the inferior olivary nucleus Video 2 • The mesencephalic nucleus of the trigeminal nerve is present at all levels of the midbrain. o The third ascending system is the spinal lemniscus (anterolateral spinal column AND spinotectal fibers) o Lastly. we have: o Substantia nigra at the junction of tegmentum and crus cerebri
Anterior to this we have corticospinal. pass through the substantia nigra and exit through the medial part of the crus cerebri
They supply levator palpabory superioris and all the extraocular muscles excepts Lateral rectus and superior oblique
CN III also receives parasympathetic fibers from the edinger westphal nucleus which lies lateral to the somatic nucleus of CN III. corticonuclear and corticopontine fibers o Cerebral aqueduct at junction of tegmentum and tectum
The medial lemniscus and spinal lemniscus are present in the anterior portion of the tegmentum o Central tegmental tract o Mesencephalic nucleus of the trigeminal system o Medial longitudinal fasciculus • Additionally. It supplies them to the ciliary ganglion which supplies fibers to the intraocular muscles o Superior colliculi which receive fibers from the visual system via the superior brachium which are coming from the lateral geniculate body. we now have: o The red nuclei which lie medial to the medial lemniscus in the anterior portion of the tegmentum o The somatic nucleus of CN III anterolateral to the cerebral aqueduct
CN III fibers move anteriorly.
It sends off tectospinal fibers for visuospinal reflexes
These are connected to each other via commissural fibers o Pretectal nuclei which lie in the tectum just anterosuperior to the superior colliculus. a posterior lobe and a flocculonodular area o Flocculonodular lobe is the most primitive part of the cerebellum (also called archecerebellum) and is concerned mainly with balance o The anterior lobe is called paleocerebellum and is concerned mainly with the tone of the muscles o The posterior lobe of the cerebellum (neocerebellum) is the most “modern” cerebellar area and is concerned with coordination of movement • The primary fissure lies between anterior and posterior lobes and the dorsolateral fissure lies between posterior and flocculonodular lobe. Role of the cerebellum in the motor functions of the body: • The idea of a movement originates in the prefrontal lobe of the cortex 31 | S A Q ’ s N a j e e b n o t e s . Posterior view of the cerebellum: • There is a longitudinal depression in the middle of the posterior aspect of cerebellum called the vermis o On either side of the vermis are the two cerebellar hemispheres o The area immediately lateral to the vermis is called paravermal area or intermediate zone. (this area is part of the cerebellar hemispheres) • Control of the trunk and other axial musculature is concerned with the vermal area whereas control of the locomotor system is concerned with the paravermal area • Cerebellum controls the balance. maintaining posture and balance and for coordination of movements • Develops embryologically from the metencephalon • Cerebellum has an anterior lobe.
They are connected to Edinger westphal nucleus
They are also connected to each other via the posterior commisures Najeeb neurosciences video set 14-Cerebellum Video 1 Introduction: • Cerebellum is mainly responsible for maintaining tone of muscles. posture and coordination of movement ipsilaterally which means that lesions would be on the same side as the clinical signs. cerebellum also samples the information at the uppermotorneuron-lowermotorneuron junction to determine whether the movement is being executed satisfactorily o It can. therefore.e. supplementary motor and primary motor cortex and the somatosensory area as well o From these areas. once the movement is initiated. the higher motor centers of the CNS consult with the cerebellum before initiating the movement • Also. also predict the result of movements occurring unhindered in the current directions o It also. These fibers release aspartate upon stimulation o All the other fibers (called mossy fibers as a group) Video 2 32 | S A Q ’ s N a j e e b n o t e s . o This idea would go to the premotor area and supplementary motor area o These areas consult with the basal ganglia o The basal ganglia make evaluations to refine the movement and send the signals to premotor. it keeps a record of the parts and orientation of the body in space o Therefore. the CNS needs to know the initial positions of the concerned muscles in space o This function is associated with the cerebellum i. the upper motor neurons originate to descend to the lower motor neurons • But for an appropriate motor program to be formulated. influences the movements to ensure that the required movement is executed (examples in lecture) Internal structure of the cerebellum: • The general arrangement is as follows: o Grey matter on the boundaries (cerebellar cortex) o White matter in the middle o Deeply residing nuclei within the white matter INPUT TO CEREBELLUM: • All the external fibers (all of these are excitatory) entering the cerebellum are input fibers and can be classified as o Olivocerebellar fibers (called the climbing fibers) which go from inferior olivary nuclei to the outermost layer of cerebellar cortex. to a very large degree. residing in the cerebellum. release GABA on surrounding purkinje cells to inhibit them OUTPUT FROM CEREBELLUM: • The output fibers are the axons of the deep nuclei The three lobes of the cerebellum: • The neocerebellum is connected to the cerebrum and is also called cerebrocerebellum (also called the pontocerebellum) 33 | S A Q ’ s N a j e e b n o t e s . on their way to the cortex. • The mossy fibers ascend up to the grenula and make multiple synapse with grenula cells o The axons of the grenula cells ascend to the molecular area where they bifurcate and run parallel in the white matter of the cortex parallel to the curvature of the cortex. a middle purkinje layer and a deep Grenula layer o Cell bodies of certain flask shaped neurons are present in purkinje area o Their dendrites lie in the molecular area o Their axons traverse the grenula on their way to synapse with deep nuclei (these are inhibitory axons and release GABA to inhibit the deep nuclei) • The climbing fibers ascend to molecular area and synapse with dendrites of the flask shaped neurons and release aspartate which is stimulatory to the flask shaped neurons o This means that the flask shaped neurons release GABA at deep nuclei and. release GABA at grenula cells to inhibit it o The other two groups are called stellate cells and basket cells which reside in purkinje layer
These are stimulated by the bifurcated parallel fibers and. too. essentially. indirectly inhibit the deep nuclei • There is an inbuilt inhibitory system. too. o One group of these is called golgi cells which are situated in the grenula layer
These can be stimulated by the bifurcated parallel fibers and by the mossy fibers and. upon stimulation. synapsing with dendrites from millions of purkinje cells on their way. the climbing fibers have indirectly inhibited the deep nuclei. o These fibers are glutaminergic (stimulatory) o Note that one mossy fiber synapses with multiple grenula cells o This means that the mossy fibers. o All the input fibers. must first synapse with the deeply residing nuclei and stimulate them PROCESSING MACHINERY IN THE CEREBELLUM: • The cerebellar cortex has an outer molecular layer. upon stimulation. VIP makes you stand) o The ascending output goes to nuclei of CN 3.4 and 6 THE SPINOCEREBELLUM: • Globose and emboliform nuclei in the cerebellum are associated with the spinocerebellum • Vermis and paravermal area receive input from the spinal cord o The dorsal spinocerebellar tract takes proprioceptive information from the lower limb and trunk to the cerebellum via the inferior cerebellar peduncle
Fibers from hip region come to vermal area and those from distal part of the limb go to the para vermal area o The cuneocerebellar pathway (THIS IS NOT COMING FROM NUCLEUS CUNEATUS) takes proprioceptive information from upper limb to the cerebellum via the inferior cerebellar peduncle
Fibers from trunk to the vermal area and those from the limbs to the paravermal area Video 3 34 | S A Q ’ s N a j e e b n o t e s . fibers (cerebellovestibular fibers) come out to synapse with and stimulate the vestibular nuclear complex. This pathway then fires up and fires down o The descending output goes to vestibulospinal tract (antigravity tract. • The palleocerebellum is connected to the spinal cord and is also called spinal cerebelleum • The archecerebellum is connected to the vestibular system and is also called the vestibulocerebellum THE VESTIBULOCEREBELLUM: • In the inner ear lies the vestibular apparatus which sends information in the vestibular nerve to either the cerebellum directly or the vestibular nuclei and then the cerebellum • The mossy fibers eventually go to the cortex through the general pathway that mossy fibers follow (mentioned in previous section) • Axons from the deep nuclei (fastigial nucleus). o The ventral spinocerebellar pathway enters the spine. through the mossy fiber pathway discussed earlier. some fibers will descend to the muscles CEREBROCEREBELLUM: • Lateral part of the cerebellar hemisphers (area lateral to paravermal area) is called cerebrocerebellum or neocerebellum. descends a little and then goes to the contralateral side while still within the cerebellum • All of the above fibers enter as mossy fibers and. fibers go to red nucleus then thalamus then motor cortex OR fibers go to thalamus then motor cortex. end up on globose and emboliform nuclei (deep nuclei) o From these nuclei information (output) goes up and down
Ascends to the red nucleus and then the thalamus and then the cortex
Ascends directly towards the thalamus and then to cortex
FROM THE RED NUCLEUS. ascends to superior cerebellar peduncle. crosses to contralateral side.
These fibers are concerned with movement and helps to make the precise movements that the cortex wanted Najeeb neurosciences video set 15-Diencephalon 35 | S A Q ’ s N a j e e b n o t e s . • Pontine nuclei receive corticopontine fibers from the cerebral cortex o Pontocerebellar fibers cross to contralateral side and enter the cerebellum via the middle cerebellar peduncle o They course as mossy fibers and synapse at dentate nucleus (deep nucleus) o From dentate nuclei. some fibers descend in the ruberospinal tract
FROM THE CEREBRAL CORTEX. inner swelling is called diencephalon
The telencephalon eventually develops into cerebral hemispheres and the diencephalon develops into thalami (there are two). o The mesencephalon remains as is in terms of vesicles. outer swelling is called telencephalon and the inferior and. epithalamus and optic nerve and chiasma. now. • The habinular nuclei along with the pineal gland constitute the epithalamus • The two thalami. now. a bundle of fibers that pass through the stalk of pineal gland. midbrain (mesencephalon) and hindbrain (rhomboncephalon) o The prosencephalon further divides into two vesicles
The superior vesicle develops much faster than the inferior one resulting in the inferior vesicle becoming buried within the superior vesicle
The superior and. Discussed in thalamus video Side note|-Anterior commisure: Connects the right and left temporal lobes of the brain Hypothalamus: 36 | S A Q ’ s N a j e e b n o t e s . hypothalamus. Video 1 and 2 combined A bit of embryology: • The CNS develops from the neural tube which develops 3 cranial swellings during development. forebrain (prosencephalon). also have an interthalamic adhesion (a mass of grey matter which sort of “sticks” the two thalami together). o The rhomboncephalon also further divides into two vesicles The diencephalon: • Lies superior to the midbrain • The cerebral aqueduct expands cranially to form the third ventricle o The third ventricle lies between the two thalami The epithalamus: o Posterior to the third ventricle lies the pineal gland/body o Habinular nuclei lie on both superoposteriolateral corners of the third ventricle
The two habinular nuclei are connected to each other (right with left and vice versa) via the habinular commisure. subthalami. continuous with the anterior and posterior pituitary glands inferiorly
The anterior pituitary is a derivative of Ruthke’s pouch and is NOT A PART OF DIENCEPHALON • Under the hypothalamus are two more swellings. o These lie posterior to the central swelling (one on the left and the other on the right side) and are called mamillary bodies Subthalami: • Lie inferior to the thalami and superior to the midbrain (consider them as butter (subthalamus) between two slices of bread (thalamus and midbrain)) Miscellaneous points: • The thalami have two swellings each on their posterior aspect. of course. the optic chiasma divides into the right and left optic tracts • Posteriorly the hypothalamus is connected to the thalami at the hypothalamic sulci o Just anterior to the hypothalamic sulci. are two “holes” in the third ventricle which are called interventricular foramen and these connect with the lateral ventricles • So. a way of thinking about the diencephalon is that it comprises of all the structures present around the third ventricle o In this regard. the medial and lateral geniculate bodies • In front of the hypothalamus. • The third ventricle anteriorly extends beyond the midbrain o The mass of grey matter anterior to the midbrain AND inferior. the third ventricle CAN be considered the cavity of the diencephalon Najeeb neurosciences video set 16-Thalamus 37 | S A Q ’ s N a j e e b n o t e s . anterior and inferolateral to the anterior aspect of the third ventricle is the hypothalamus • Under the hypothalamus is a central swelling o The swelling is called the median eminence (the superior part of the median eminence is called the tubercinerium) o The median eminence is continuous inferiorly with the stalk of the pituitary gland o The stalk is then. The notes are made with the assumption that you have already watched diencephalon. • Thalamus is a very large mass of grey matter and has a “Y” shaped white matter lamina in the middle called the internal medullary lamina o The lamina divides the thalamus into medial. o This has a bend which complements the bend of the lentiform nucleus and it is called the internal genu of the internal capsule • Lateral to these bundles are masses of grey matter called the lentiform nuclei 38 | S A Q ’ s N a j e e b n o t e s . anterior and lateral thalamus
The lateral thalamus is further divided into ventral and dorsal parts • The dorsal part consists the dorsal tier nuclei • The ventral part consists the ventral tier nuclei o Thalamic nuclei are connected to each other via fibers which reside in the internal medullary lamina • There is a “sheet” of white matter on top of the thalamus called the stratum zonale • There is another “sheet” of white matter on the lateral aspect of the thalamus called the external medullary lamina • Between the two thalami. This bundle is called internal capsule. you should have watched diencephalon videos before starting this. It will make stuff much easier. it is considered part of the thalamic nuclear group Anatomical relationship of the structures at the base of the brain: The structures mentioned in this section are IN ADDITION to the ones already mentioned in diencephalon notes (refer to that lecture for an overview of diencephalon) • Lateral to the external medullary lamina of the thalami are thick bundles of white matter which contain both ascending and descending fibers. Video 1 Note: Preferably. Introduction: • The two thalami constitute the largest part of the diencephalon. there is interthalamic adhesion (grey matter) • On the posteroinferior aspect of the thalamus lie the lateral geniculate body connected to the visual system and the medial geniculate body connected to the auditory system. • Another nucleus lies on the outer aspect of the external medullary lamina anterolateral to the thalamus o This is called the reticular nucleus o Even though this lies outside the thalamus.
It is responsible for anger and certain primitive feelings like sexual ones. superior (body) and posterior (tail) to the thalamus. This bundle is called external capsule • The caudate nucleus lies anterior (head). o The lentiform nucleus is divided into two parts
The lateral part is called the putamen
The medial part is called the globus pallidus (something like that) • Lateral to the lentiform nuclei are thin sheets of white matter again. in close association with the temporal extension of the lateral ventricle lie the hippocampal and parahippocampal areas o From the parahippocampal area. a bundle of white matter (fornix) extends to the mammilary body of the hypothalamus Video 2 • Stria terminalis (najeeb isn’t sure) is a bundle of white matter extending from amygdaloid body to the hypothalamus Thalamus: • Posterolaterally. the thalamus has a free margin called the pulvinar • The anterior and dorsomedial (same as medial) nucleus are concerned with the limbic system (This system is concerned with behavior and emiotions) ANTERIOR THALAMIC NUCLEUS 39 | S A Q ’ s N a j e e b n o t e s . o The part anterior to the thalamus extends laterally to the lentiform nucleus and so does the posterior part o The posterior part of the caudate nucleus has a small amygdaloid body attached to it but the amygdaloid body is NOT part of the caudate nucleus. • The third ventricle has two openings (interventricular foramen) which connect it to the lateral ventricle o The lateral ventricle extends anteriorly into the frontal lobe o Its body lies above the thalamus and in the parietal lobe o It extends posteriorly into the occipital lobe o It extends laterally into the temporal lobe • In the temporal lobe. o The part of the cerebral cortex associated with this function is the frontal lobe.
All the motor activity of the other thalamic areas also goes through the medial thalamic nucleus o Lentiform nucleus is also heavily connected to the dorsomedial nucleus INTRALAMINAR NUCLEI • Although it is a sheet of white matter. o The entire circuit from the parahippocampus to singulate gyrus is called papez circuit and is concerned with recent memory. o CC: in severe thiamine deficiency. fibers would carry this information to the singulate gyrus. From the mamillary body. • Its major function is to adjust mood in reference to recent memories (e. o Medial thalamic nucleus receives input from all the other areas of thalamus
Remember that all the sensory information passes through thalamus EXCEPT olfactory. fibers go to the anterior nucleus of the thalamus (the mamillothalamic tract) o From the anterior thalamic nucleus. happiness on hearing good news) • This nucleus is in intimate relationship with the limbic system • Most of the fibers of fornix terminate in the mamillary body. particularly the prefrontal cortex. there are loads of action potentials in this circuit which explains why emotionally significant memories are almost always long-term. o These nuclei are closely related with the reticular formations • Connections: o The ascending reticular formation connects with the intralaminar nuclei 40 | S A Q ’ s N a j e e b n o t e s . there aren’t many action potentials in the papez circuit but in the opposite scenario. mamillary bodies will degenerate resulting in patient developing amnesia. o When information that doesn’t carry a high emotional component is received. MEDIAL THALAMIC NUCLEUS • The most important nucleus in this region is the dorsomedial nucleus • This area functions to adjust behavior and psychological and physical state in accordance with the mood of the person.g. • Connections: o Medial thalamic nucleus is connected to prefrontal cortex. the internal lamina has collections of grey matter within it called the intralaminar nuclei. amygdala and clostrum are considered basal ganglia o Clinically. • Severe pain can cause the intralaminar nuclei to be damaged • The largest intralaminar nucleus is the centromedian nucleus. caudate nucleus. subthalami and the substantia nigra are considered basal ganglia. o Some of the spinothalamic pain fibers connect directly with the intralaminar nuclei o Certain fibers from the head carry pain-related information through the trigeminothalamic system and these also connect with the intralaminar nuclei o Also connected to all other thalamic nuclei • The intralaminar nuclei then send information via fibers connected to all of the cortex o This pathway just described is concerned with cerebral arousal and keeping the cerebral cortex “activated”. caudate nucleus. lentiform nucleus. o This nucleus is connected to the rest of the thalamus o This nucleus is also connected to the motor cortex and basal ganglia o It can regulate the level of arousal Najeeb neurosciences video set 17-Basal nuclei Video 1 Introduction: • Masses of grey matter at the base of the cerebral hemisphere • Lateral to the lentiform nucleus was the external capsule o Lateral to external capsule is another mass of grey matter called the clostrum o Lateral to clostrum is another bundle of white matter called the extreme capsule o Insula is a mass of grey matter • The posterior part of the substantia nigra (midbrain structure) is called pars compacta • The basal ganglia are classified using either traditional or clinical classification o Traditionally. (this video follows this classification) Terminology: • Globus pallidus of the lentiform nucleus is divided into medial (internal) and lateral (external) parts • The lentiform nucleus and the caudate nucleus are collectively called corpus striatum 41 | S A Q ’ s N a j e e b n o t e s . lentiform nucleus. ventrolateral and dorsomedial nuclei of thalamus 42 | S A Q ’ s N a j e e b n o t e s . the motor cortex isn’t stimulating this pathway o Pallidothalamic fibers are very active in this state. pre and supplementary motor areas as well as somatosensory area of the cortex • When the idea of a movement is thought in the prefrontal cortex. releasing GABA on ventroanterior. via the thalamus send this refined signals to the four areas mentioned in the previous bullet. thalamocortical fibers connect back to the cortex • The neurotransmitter released by corticostriatal and thalamocortical fibers is glutamine o The glutamate receptor at post synaptic membrane causes cation influx when glutamine attaches o The striatopallidal fibers and the pallidothalamic fibers release GABA and substance P as their neurotransmitters • Under conditions of rest. These are programs that are executed for movements to occur. Watch the video alongside reading the following description to avoid getting confused • Cortical fibers descend to stimulate fibers in the putamen and are called corticostriatal fibers o From the putamen. it is transmitted to pre and supplementary motor cortex o These then send signals to the basal ganglia which refines the movement and. fibers go to the globus pallidus internal (striatopallidal fibers) o From the GPI. • The putamen of the lentiform nucleus and the caudate nucleus collectively are called neostriatum or just striatum • The globus pallidus is called paleo striatum Functional perspective of the basal ganglia: • Motor plans are stored in basal ganglia and cerebellum. Video 2 The basal ganglia: THE STIMULATORY PATHWAY: Note: GABA will inhibit postsynaptic neurons and glutamate will stimulate postsynaptic neurons. o This means that the basal ganglia have activity occurring even before the movement occurs • Corticospinal and corticonuclear fibers originate from primary. pallidothalamic fibers connect to thalamus o From the thalamus. o GABA can hyperpolarize the postsynaptic membrane via either Cl influx or K efflux and this keeps the thalamocortical fibers inhibited • Under conditions of activity. fibers go to globus pallidus EXTERNAL o From globus pallidus EXTERNAL. fibers go to subthalamus o From subthalamus. to which dopamine binds and stimulates the neuron o The striatopallidal fibers of the inhibitory pathway have D2 receptors. the motor cortex stimulates this pathway o The corticostriatal fibers stimulate striatopallidal to release GABA at pallidosubthalamic fibers o Pallidosubthalamic fibers are inhibited and thus DON’T release much GABA on subthalamopallidal fibers o So now subthalamopallidal fibers are stimulated to release glutamate on pallidothalamic fibers o Pallidothalamic fibers are stimulated to release GABA on thalamocortical fibers o Thalamocortical fibers are thus inhibited and motor centres ARE NOT STIMULATED SUBSANTIA NIGRA’s ROLE: • Dopaminergic fibers from pars compacta synapse at the striatopallidal fibers of both the stimulatory and the inhibitory pathways o These dopaminergic fibers facilitate the initiation of the movement o The striatopallidal fibers of the stimulatory pathway have D1 receptors. essentially. thalamocortical are now disinhibited and can now fire and stimulate the motor cortex via glutamate THE INHIBITORY PATHWAY: • Cortical fibers descend to stimulate fibers in the putamen and are called corticostriatal fibers o From putamen. dopaminergic firing on both the striatopallidal fibers results in stimulation of motor cortex 43 | S A Q ’ s N a j e e b n o t e s . fibers go to thalamus • Under conditions of rest. fibers go to globus pallidus INTERNAL o From GPI. to which dopamine binds and inhibits the neuron o So. corticostriatal fibers are stimulated to release glutamate o This stimulates striatopallidal fibers to release GABA at pallidothalamic fibers o GABA inhibits pallidothalamic release of GABA at thalamocortical fibers by the mechanism described earlier o Since pallidothalamic fibers are now inhibited. HUNTINGTON’s disease: 44 | S A Q ’ s N a j e e b n o t e s . the reticular formation is over-stimulated and muscle tone is increased both on flexors and extensors
This means that it is difficult to cause any movement since the antagonist muscles for that movement is stimulated o Tremors:
Dopaminergic activity is low in this disease which means that the cholinergic activity is now unchecked
There are reverberation circuits within the lentiform nuclei and with loss of dopaminergic activity. rigidity and tremors o Hypokinesia:
Hence. • Corticonigral fibers form the cortex synapse at substantia nigra so that the cortex can communicate with the substantia nigra so it knows whether the movement is to be stimulated here • Pars reticularis can be functionally considered inferiorly displaced globus pallidus internal CHOLINERGIC NEURONS: • Within the striatum lie cholinergic neurons which antagonize dopamine’s actions on the stimulatory and inhibitory pathways Pathologies: PARKINSON’s • This disease degenerates neurons in pars compacta resulting in less release of dopamine from nigrostriatal pathway resulting in hypokinesia. DISEASES WITH HYPERKINESIA: 1. these circuits keep alternatively stimulating flexors and extensors unchecked resulting in tremors • Parkinson like situations can occur in patients undergoing therapy with anti- dopaminergic drugs and with MPTP. the stimulatory pathway discussed earlier is inhibited as a whole
Hence. the inhibitory pathway discussed earlier is stimulated as a whole
This leads to the motor cortex remaining inhibited to a certain degree o Rigidity:
Corticoreticular fibers function to inhibit reticular formation
Since cortex is inhibited as already mentioned. Motor cortex releases motor programs in a haphazard fashion >>Athetosis: slow writhing dancelike movements resulting from damage to GABArgic neurons in inhibitory pathway >>Dystonias: overcontraction of axial muscles resulting from damage to GABArgic neurons in inhibitory pathway >>Hemi ballismus: damage to subthalamus (classically in diabetic or hypertensive individuals) which is unilateral so that only one thalamus is affected. erratic movements of hip and shoulder girdles) appear on the contralateral side of lesion >> Tardive dyskinesia: classically in pts. Clinical features (sudden. sydenham’s. Wilson disease): sudden brisk dance-like movements resulting from damage to GABArgic neurons in inhibitory pathway. • Striatopallidal fibers of the inhibitory pathway are damaged • This will eventually lead to inhibitory pathway being “shut down” and the inhibitory effect will not be there anymore o This will lead to overstimulation of cerebral cortex resulting in hyperkinesia or dyskinesia • Etiology: Trinucleotide (CAG) repeats on chromosome 4. Dopamine receptor upregulation occurs with long term use. 45 | S A Q ’ s N a j e e b n o t e s . Taking dopamine receptor blockers. Head of caudate nucleus degenerates and lateral ventricle appears abnormally large Side note-types of hyperkinesia >>Chorea (huntington’s. Superior rectus (SR) and inferior oblique (IO). o The clinical significance here is that irritative lesions from the top would cause excessive parasympathetic activity leading to miosis (pinpoint pupil). 46 | S A Q ’ s N a j e e b n o t e s . IO and IR o The superior division supplies SR and levator palpabre superioris (eyelid)
The levator palpabre superioris also receives fibers from the sympathetic innervations (this part of the muscles is called the muller’s muscle). moves anteriorly to sling around the trochlea and attach to the eye o SO4-Superior oblique is supplied by the 4th nerve o LR6-Lateral rectus is supplies by the 6th nerve Anatomy: • Course: o 3rd nerve enters the orbital cavity and divides into superior and inferior divisions
The parasympathetic fibers wouold go along the inferior division o The inferior division supplies MR. enter the orbit • Of the extraocular muscles. Inferior rectus (IR).
Muller’s muscle is used to elevate eyelids unconsciously whereas the other part is used to elevate eyelids voluntarily rd • The 3 nerve exits very close to posterior cerebral and posterior communicating arteries and abnormal vasodilation of these can result in 3rd nerve palsies • The parasympathetic fibers lie peripherally in the nerve (especially in the superior part of the nerve) and the somatic efferents lie central to them. Najeeb neurosciences video set 19-Oculomotor nerve palsies Video 1 The oculomotor nerve: • Has general somatic efferents from the third nerve nucleus and has general visceral efferents (parasympathetic fibers) from the edinger westphall nucleus o They exit from the medial side of crus cerebri in the upper level of midbrain o They pass through the interpeduncular fossa and approach the lateral wall of the cavernus sinus • In the orbit lies the superior orbital fissure behind which lies the cavernus sinus o Within the lateral wall of the cavernus sinus. the oculomotor nerve supplies the Medial rectus (MR). through the superior orbital fissure. o The superior oblique originates from posterior part of the orbit. these fibers (oculomotor nerve) move anteriorly and. we think of medical causes when general somatic efferent effect is more pronounced • Diabetes mellitus can cause oculomotor palsy which can cause general somatic efferent failure and later on progresses to parasympathetic fibers • In oculomotor palsy. o Once these lesions start destroying the parasympathetic fibers. we think of surgical reasons and. Palsies: • If parasympathetic effect is more pronounced. pupiloconstriction is compromised and the pupil is dilated o The patient also develops diplopia (double vision) since the axes of both eyes are not aligned o Paralysis of accommodation occurs due to lack of innervations to ciliaris (cycloplegia) 47 | S A Q ’ s N a j e e b n o t e s . patient now experiences pupilodilation. LR and muller’s muscle remain intact o The upper lid droops down since levator palpabre superioris is compromised (ptosis) o The eyeball is displaced outward (LR) and downward (SO) o Since parasympathetic fibers are gone. otherwise. only the SO. supply sphincter pupilli. still. o Parasympathetic fibers reach ciliary ganglion and some of these supply Internal oblique. others supply ciliaris and others. The vertebrobasilar system: • There are foramina in the transverse processes of cervical vertebra through which vertebral arteries pass and through the foramen magnum. which is surrounded by arachinoid matter. which is surrounded by subarachinoid space (full of CSF). they enter the cranial cavity. o The two vertebral arteries (one from each subclavian artery) move forward upward and medially over the medulla and meet at the pontomedullary junction following which they ascend as one basilar artery. which is surrounded by duramatter. o carotid (Internal carotid arteries) system which is also called the anterior system o vertebral arteries (lie posteriorly and ascend medially behind the Internal carotid arteries) which are also called the posterior system or the vertebrobasilar system. • All the major arteries that enter the cranial cavity lie in the subarachinoid space o This means that these major arteries have to pierce the duramatter. • CNS is surrounded by piamatter. Anterior spinal artery (ASA) • Course: o Branches (right and left) come off the lower part of vertebral arteries in front of the medulla o These unite in front of the lower part of the medulla and make the anterior spinal artery which descends in the anterior median fissure of the spine • Anterior two thirds of the spinal cord are supplied by ASA: o A blockade in ASA will result in anterior 2/3rd of spinal cord in that blocked region getting infracted • Multiple segmental arteries reinforce ASA: 48 | S A Q ’ s N a j e e b n o t e s . Najeeb Neurosciences Video set 30-Blood supply to the brain Video 1 • About 15% of the cardiac output is dedicated to the CNS • Blood goes to CNS via two systems namely. Vertebral arteries originate from the subclavian arteries. o The basilar artery gives off terminal branches just above the exit of CN III which are the right and left posterior cerebral arteries Branches of the vertebrobasilar system: 1. o Berry aneurysms are commonly present in the circle of villus and when these rupture they produce a haemorrhage in the subarachinoid space. o These segmental arteries come from the left and right sides of the body as ASA descends o As these segmental arteries move medially. they divide into anterior and posterior reticular branches
The anterior branches reinforce ASA’s blood flow
The posterior branches reinforce blood flow in Posterior spinal arteries (there are two) Side note: >>There are three important groups of segmental arteries which reinforce blood flow in the spinal arteries: Deep cervical arteries in the neck region Intercostal arteries in the thoracic region Lumbar arteries in the lumbar region >>The most important reinforcer of blood flow for ASA is called the great medullary artery of Adamkiewicz. Posterior inferior cerebellar artery: (PICA) • Supplies lateral medulla in addition to posterior inferior surface of the cerebellum 4. >>The weakest blood supply from ASA in the spinal cord is at two points: At the level of T4 At the level of L1 These two are the most likely sites of infarction in case of a blockade >>The weakest blood supply from PSA is at the level of T1. Anterior inferior cerebellar artery: (AICA) • Originate either from the superior part of vertebral arteries or lower part of basilar artery • Supplies lateral pons in addition to anterior inferior surface of cerebellum 49 | S A Q ’ s N a j e e b n o t e s . a big part of spinal cord may undergo infarction.T2 and T3 2. Posterior spinal arteries: (PSA) • Either come directly off vertebral arteries or come off PICA (see below) • Descend on the posterior side of the spinal cord 3. If this is blocked. o Supratrochlear artery o Supraorbital artery o Some more were mentioned really fast… 50 | S A Q ’ s N a j e e b n o t e s . these arteries lie on each side of the pituitary gland Branches from the carotid system: 1. Superior cerebellar artery: • Originate under CN III off the basilar artery 8. Pontine arteries: • Branch off basilar artery 7. o To further add detail. Posterior cerebral arteries: • Supply midbrain. they may block retinal artery and unilateral blindness will result in the eye supplied by that retinal artery. basilar artery 6. Ophthalmic artery: (anterior branch) • Enters the orbital cavity through the optic canal • Gives off further branches: o Central retinal artery
CC: Thrombi from left atrium or mitral or aortic valve may dislodge and if they come into carotid circulation.5. Labyrinthine arteries: • Branch off AICA or less commonly. temporal lobe’s inferior area and occipital lobe Video 2 The carotid system: • The internal carotid arteries move superiorly and enter via carotid canal at the undersurface of the base of the cranium and enters the middle cranial fossa via foramen lacerum o It pierces the duramatter in this region to find itself inside the cavernus sinus where it moves upward to pierce arachinoid matter to enter the subarachinoid space. a horizontal branch which comes off the anterior cerebral arteries on either side and serve to link the anterior cerebral arteries with each other • This artery is the most common site of berry aneurysms.2. • As it travels the sulcus. of course. • If middle cerebral artery is occluded. among other branches. 51 | S A Q ’ s N a j e e b n o t e s . are part of the vertebrobasilar system 3. it gives off striatal branches which go into deeper structures in the corpus striatum. Middle cerebral artery (moves laterally) • Moves laterally through the lateral sulcus until it appears on the superolateral surface of the cerebral hemisphere. • They are linked via the anterior communicating artery. foot and leg will be spared since these regions of the brain are supplied by the anterior cerebral artery but the other parts of the body will experience weakness (see homunculus to understand this concept) 6. Anterior cerebral artery (moves anteriorly) • Moves anteriorly and arches upward and backwards to arch over corpus collosum • Gives cortical branches to the medial surface of frontal lobe and parietal lobe and these branches also supply the upper part of frontal and parietal lobes 5. • Gives off further branches after reaching lateral end of lateral sulcus and these branches Fan out. Anterior communicating artery • Similarly on the opposite side. Posterior communicating artery: (posterior branch) • This artery links carotid and vertebrobasilar system • They are given off posteriorly from each internal carotid artery and link with the posterior cerebral arteries on each side (these. anterior and middle cerebral arteries will be given off. Anterior coroidal artery: (posterior branch) • Supplies the coroid plexus of the lateral ventricle 4. Side note|-Circle of villus: Connects the right carotid system with the left carotid system and links the anterior carotid circulation with the posterior carotid circulation and also link the carotid circulation with the vertebrobasilar system. 2. The ACAs are linked via anterior communicating artery (makes the anterior border of the circle) 3. The posterior communicating branches link up with the posterior cerebral arteries and the posterior cerebral arteries make up the posterior border of the circle So this unique type of collateral blood supply compensates for blockade in any one part of the circulation through these anastomoses. What happens is this: 1. 4. The carotid arteries also give off posterior communicating branches (see ‘2. Internal carotid arteries give off anterior cerebral arteries (make the anterolateral border of the circle of villus).’ Above) (which form the posterolateral and lateral borders of the circle). 52 | S A Q ’ s N a j e e b n o t e s . So it is present in subarachinoid space under the base of the brain in front of the mid brain and under the cerebral hemispheres.