Model 1 – Alteration of Resting Membrane PotentialQuestions 1. Resting Membrane Potential (RMP) is the potential difference that exists across a membrane of a cell. What is the RMP for a typical neuron shown in model 1? -70mv 2. Depolarization and hyperpolarization are two types of membrane potentials. For the following values determine if the membrane is depolarized or hyperpolarized a) 0 mV - Depolarized d) -70 mV - RMP b) -100 mV - Hyperpolarized e) -69 mV - Depolarized c) -71 mV - Hyperpolarized f) +30 mV - Depolarized 3. Voltage is a recording of inside charge compared to the outside charge. Write a grammatically complete sentence to define each RMP alteration: a) Depolarization: Change in the voltage more positive because it’s above -70 RPM b) Hyperpolarization: Change in the voltage more negative because it’s below - 70RPM Model 2 – Ion Movement Across Neuronal Membrane Neurons use changes in membrane potential as communication signals (nerve impulses). The RMP changes are due to ions crossing the plasma membrane through specific ion channels. Questions 4. Sodium Ion Movement: a) What do you notice about the sodium in this diagram? There is more NA outside compared to the inside of the Neuron Membrane. There are only positive electrons along the ring The Ion channel is positive. b) What conclusions can you make about sodium movement and cell charge in relation to a neuron? As the Na moves through the cell, it starts to move to the side that has less due to diffusion, trying to balance the levels of Na. (Diffusion: From high concentration to low concentration) 5. Potassium Ion Movement: a) What do you notice about the potassium in this diagram? There is more K inside the cell compared to the outside. b) What conclusions can you make about potassium movement and cell charge in relation to a neuron? 6. a) First answer the following question individually, not with your group. Predict the RMP alteration that would occur with each ion movement. Use the terms depolarization and hyperpolarization to complete the below table. Ion Influx (into cell) Efflux (out of cell) Anion (-) Hyperpolarization Depolarization Cation (+) Depolarization Hyperpolarization b) Within your group, discuss your individual answers. As a group come to a consensus and then label the table on the recorder sheet. The answer must be agreed on by all group members. 7. In a resting neuron there is greater K+ permeability than Na+ permeability. What would happen to the RMP if Na+ and K+ permeability were the same? The charge would be 0 because the diffusion would balance out the Na and the K. Model 3 – Action Potential Model 3 shows a typical neuron action potential. Action potentials are brief reversals of membrane potential in response to a stimulus. Action potentials travel along the axon, and method of how neurons communicate. Questions 8. What do you notice about the graph? ➢ when a neuron is affected by a stimuli mV increases rapidly ➢ Looks like a sinusoid (Kinda) ➢ Multiple stimuli that don’t cause action potential 9. Determine the voltage range for the four phases of the action potential. 1) Resting = -70 RMP 2) Depolarization = 30 RMP 3) Repolarization = -100 RMP 4) Hyperpolarization = -100 RMP 10. Action potentials traveling along a neuron are due to the opening and closing of sodium and potassium ion channels. Predict if the Na and K channels are open or closed in each phase. Place your answers in the above table. Action # Potential Phase Sodium (Na+) Potassium (K+) 1 Resting closed closed 2 Depolarization open closed 3 Repolarization close open 4 Hyperpolarization close open 11. What conclusions can you make about the action potential from the table above? K acts more as a negative rather than a positive. To depolarize, you must add more Na to the membrane To hyperpolarize, you must add more K to the membrane 12. The ion channels are opening and closing at different parts of the action potential. What type of gated ion channel is used for an action potential (chemical, mechanical, voltage)? The channels are voltage 13. Examine the model. What must be reached in order to initiate an action potential (be specific)? When different ions cross the neuron membrane and when affected by a stimuli that make it become positive. 14. Action potentials have an all-or-none principle. As a group, write a grammatically correct sentence to explain what is meant by this phrase. 15. Although stimulus originate at the dendrite and travels through the cell body, an action potential does not start until the axon hillock. Postulate why action potentials do not occur on dendrites (even with a very strong stimulus) and why action potentials first start at the axon hillock. Review questions: 16. When a Potassium voltage-gated-channel opens in a neuron at rest, what will happen to RMP: no change, depolarization, repolarization, or hyperpolarization? 17. A drug that opens sodium channels in a motor neuron would ____________ the membrane. Predict how this drug would affect the probability of generating an action potential. 18. Novacaine and lidocaine are two local anesthetic drugs used in dentistry. Anesthetics block nerves from sending action potentials to the nerve. Determine possible mechanisms of action for novocaine.