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UNC-Chapel Hill BIOL 252 - Homework 1 KEY

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Homework 1 (Lessons 3-5) Q1. If the membrane potential of a segment of axolemma is -60mV, which statement about the movement of Na+ ions is true? (X) Na+ ions will move into the axoplasm ( ) Na+ ions will move out of the axoplasm ( ) Na+ ions will not move Q2. How many of the below are involved in the production and maintenance of a neuron's negative resting membrane potential? A. Sodium voltage-gated ion channel B. Potassium voltage-gated ion channel C. Potassium leak channel D. Sodium ligand-gated ion channel E. Na/K ATPase ( ) 0 ( ) 1 (X) 2 ( ) 3 ( ) 4 ( ) 5 Q3. What is unique about the Nodes of Ranvier that allow them to propagate action potentials? (X) They are enriched with voltage-gated ion channels ( ) They have double the myelin layers as internodes ( ) They allow Na+ to passively diffuse across the membrane ( ) They have thinner axolemma then the rest of the axonQ4. How many of the statements below about local potentials are TRUE? A. Local potentials cause either depolarization or hyperpolarization B. Local potentials can initiate an action potential C. Local potentials signal travels a consistent distance [this is the false statement] D. The size of a local potential is proportional to strength of stimulus ( ) 0 of the statements above are true ( ) 1 of the statements above are true ( ) 2 of the statements above are true (X) 3 of the statements above are true ( ) 4 of the statements above are true Q5. An axon that is at resting membrane potential receives a local potential that causes the axolemma to hyperpolarize. Which of the following is specifically causing the cell to hyperpolarize? ( ) Na+ ions are moving out of the axoplasm via facilitated diffusion (X) K+ ions are moving out of the axoplasm via facilitated diffusion ( ) Na+ ions are moving out of the axoplasm via active transport ( ) K+ ions are moving out of the axoplasm via active diffusionQ6. Referring to the graph above, which number on the graph represents when voltage-gated sodium channels are in the activated state? ( ) 1 (X) 2 ( ) 3 ( ) 4 Q7. Which of the following statements about saltatory conduction is TRUE? ( ) Saltatory conduction occurs during the depolarization phase, when voltage-gated Na+ channels are activated ( ) Saltatory conduction occurs when both Na+ and Cl- are able to move across the membrane through their respective channels ( ) Saltatory conduction occurs when a local potential is strong enough to fire another action potential in the relative refractory period (X) Saltatory conduction occurs in axons that are myelinated, allowing the action potential to be propagated the length of the internodesQ8. Electrical synapses are capable of transmitting signals in a bidirectional manner. (X) True ( ) False Q9. How many of the following would occur if the receptor for a neurotransmitter were blocked? 1) Calcium channels in the presynaptic neuron would open 2) Neurotransmitters would be released by the presynaptic neuron 3) An IPSP would be generated in the postsynaptic neuron 4) Voltage-gated sodium channels in the postsynaptic neuron would activate ( ) 0 of the above would occur ( ) 1 of the above would occur (X) 2 of the above would occur ( ) 3 of the above would occur ( ) 4 of the above would occur Q10. Which best describes the phenomenon depicted in the illustration of the membrane potential in the axon below? ( ) Temporal summation and a single EPSP ( ) Spatial summation and a single EPSP (X) Temporal summation and multiple EPSPs ( ) Spatial summation and multiple EPSPsQ11. Donepezil is a medication that is commonly used to treat Alzheimer’s disease and acts by inhibiting acetylcholinesterase. This suggests that Alzheimer’s disease is associated with which of the following? ( ) Reduced activity of Na voltage gated ion channels ( ) Inhibited activity of presynaptic neurons ( ) Overactive postsynaptic neurons (X) Inhibited activity of postsynaptic neurons Q12. Which of the following would you expect to happen in a postsynaptic neuron that received an IPSP signal? ( ) Activation of voltage-gated sodium ion channels (X) Activation of ligand-gated potassium ion channels ( ) Activation of ligand-gated calcium ion channels ( ) Activation of voltage-gated potassium ion channels Q13. What specific type of gated channel opens or closes in response to physical distortion of the membrane surface, such as vibrations or pressure? ( ) Voltage-gated ( ) Chemically-gated (X) Mechanically-gated ( ) Ligand-gated Q14. Which is most likely to promote an action potential? (X) Depolarization of the axolemma ( ) Hyperpolarization of the axolemma ( ) Repolarization of the axolemma Q15. During the absolute refractory period: ( ) Each stimulus produces an action potential ( ) A strong stimulus can produce an action potential ( ) Sodium ion channels are in their resting state (closed). (X) No additional stimulus, no matter the strength, can produce an additional action


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