Question 1

Which of the following factors influences the conduction velocity of the action potential through the axon?&#10;A) Axon diameter&#10;B) Myelin thickness&#10;C) Ion channel density&#10;D) All of the above

Accepted Answer

All of the factors listed influence the conduction velocity of the action potential through the axon. A larger axon diameter reduces resistance to the flow of ions, speeding up conduction. Myelin sheaths increase conduction speed by allowing the action potential to jump between nodes of Ranvier in a process called saltatory conduction. Ion channel density affects how quickly ions can enter or exit the axon, influencing the speed of action potential propagation.

Question 2

In the normal axon, reverse propagation of the action potential is not possible because the membrane is&#10;A) Refractory because of sodium channel inactivation&#10;B) Refractory owing to potassium channel inactivation&#10;C) Refractory as a result of sodium ion influx&#10;D) Refractory because of potassium ion influx&#10;E) At its resting potential

Accepted Answer

The refractory period in an axon, during which reverse propagation of an action potential is not possible, is primarily due to the inactivation of sodium channels. After an action potential, these channels close and cannot immediately reopen, preventing the backward movement of another action potential.

Question 3

A 31-year-old woman is diagnosed with depression and prescribed a selective serotonin reuptake inhibitor. Which of the following is a precursor of serotonin?&#10;A) Lysine&#10;B) Glutamine&#10;C) Tryptophan&#10;D) Histidine&#10;E) Threonine

Accepted Answer

Tryptophan is the amino acid precursor to serotonin, a neurotransmitter involved in mood regulation, among other functions. SSRIs work by increasing serotonin levels in the brain.

Question 4

Which of the following is considered the rate-limiting step in the synthesis of acetylcholine?&#10;A) Transport of choline into the neuron&#10;B) Acetylcholinesterase production&#10;C) Choline acetyltransferase activity&#10;D) Acetyl CoA availability

Accepted Answer

The transport of choline into the neuron is considered the rate-limiting step in the synthesis of acetylcholine, as it determines the availability of choline to be acetylated by choline acetyltransferase.

Question 5

The stimulus intensity required to initiate an action potential is referred to as which of the following?&#10;A) Saturation&#10;B) Threshold&#10;C) Adaptation&#10;D) Frequency coding&#10;E) Refractory period

Accepted Answer

Threshold is the correct term for the minimum level of stimulus intensity required to initiate an action potential in a neuron.

Question 6

Which of the following most accurately represents the order of events for transmission at a G-protein coupled receptor?&#10;A) Activation of a G-protein, binding of the neurotransmitter, activation of the effector&#10;B) Binding of the effector, binding of the neurotransmitter, activation of a G-protein&#10;C) Binding of the neurotransmitter, activation of a G-protein, activation of the effector&#10;D) Activation of the effector, binding of the neurotransmitter, activation of a G-protein&#10;E) Binding of a G-protein, binding of the neurotransmitter, activation of the effector

Accepted Answer

The correct sequence for transmission at a G-protein coupled receptor is: binding of the neurotransmitter to the receptor, which then activates a G-protein, followed by the activation of an effector enzyme or ion channel. This sequence ensures the proper transmission of signals across the cell membrane.

Question 7

High concentrations of acetylcholine maintained at the neuromuscular junction for several seconds would result in which of the following?&#10;A) Desensitization&#10;B) Hyperexcitation&#10;C) Inhibition&#10;D) Saturation&#10;E) Recruitment

Accepted Answer

Desensitization occurs because prolonged exposure to acetylcholine can lead to the inactivation of acetylcholine receptors at the neuromuscular junction, reducing their responsiveness.

Question 8

A research scientist is interested in the effects of various toxins on the action potential in nerve cells. During one of the electrophysiological tests, the scientist injects tetrodotoxin (TTX) into the bathing solution. Which aspect of the action potential will most likely be affected by the injection of TTX?

A) Depolarization due to K⁺ channel blockade
B) Depolarization due to Na⁺ channel blockade
C) Depolarization due to Na⁺ channel opening
D) Hyperpolarization due to K⁺ channel blockade
E) Hyperpolarization due to Na⁺ channel blockade

Accepted Answer

Tetrodotoxin (TTX) is known to block sodium (Na+) channels, which are crucial for the depolarization phase of the action potential in nerve cells. By blocking these channels, TTX prevents the influx of Na+ ions, thereby inhibiting depolarization.

Question 9

The undershoot of the action potential is primarily attributable to which of the following?&#10;A) Sodium influx&#10;B) Sodium efflux&#10;C) Potassium influx&#10;D) Potassium efflux

Accepted Answer

The undershoot of the action potential, also known as the hyperpolarization phase, is primarily due to potassium efflux. During this phase, potassium channels remain open longer than sodium channels, allowing more potassium to leave the cell than is necessary to return to the resting potential, thus causing the membrane potential to become more negative than the resting potential.

Question 10

Connections to the globus pallidus from the putamen are an example of an inhibitory synapse in the central nervous system that utilizes which of the following neurotransmitters?&#10;A) Glutamate&#10;B) Gamma-aminobutyric acid&#10;C) Diacylglycerol&#10;D) Adenylyl cyclase&#10;E) Enkephalin

Accepted Answer

Gamma-aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system, and it is used in the inhibitory synapses between the putamen and the globus pallidus.

Deck 11: Organization of the Brain Stem