Question 1

Which of the following best explains why action potentials are able to travel long distances along an axon without losing amplitude?

Accepted Answer

Action potentials are regenerated at each segment of the axon by voltage-gated Na\+ channels, ensuring the signal remains strong.

Question 2

A patient presents with muscle weakness and slowed nerve conduction. Laboratory tests reveal demyelination of peripheral nerves. Which of the following best explains the physiological basis for the slowed conduction velocity?

Accepted Answer

Increased current leak in unmyelinated regions causes the depolarization wave to become subthreshold before reaching the next node.

Question 3

Which equation best represents the relationship between axon diameter and resistance to current flow?

Accepted Answer

$$R \propto \frac{1}{d^2$}$$

Question 4

Which of the following would most likely increase the velocity of action potential conduction in a neuron?

Accepted Answer

Increasing the axon diameter and adding myelin sheaths.

Question 5

Local anesthetics block voltage-gated Na\+ channels. What is the most direct effect of this on neuronal signaling?

Accepted Answer

Action potentials cannot be initiated or propagated, leading to loss of sensation.

Question 6

Which of the following best describes the difference between ionotropic and metabotropic neurocrine receptors?

Accepted Answer

Ionotropic receptors are ligand-gated ion channels that mediate fast postsynaptic responses, while metabotropic receptors are G-protein coupled and mediate slower, modulatory responses.

Question 7

A neuron is exposed to a solution with elevated extracellular K\+ concentration. What is the most likely effect on the resting membrane potential?

Accepted Answer

The resting membrane potential becomes less negative (depolarizes).

Question 8

Which of the following is TRUE regarding graded potentials?

Accepted Answer

Graded potentials decrease in amplitude as they travel away from the site of origin due to current leak.

Question 9

Which of the following best describes the role of the nodes of Ranvier in myelinated axons?

Accepted Answer

They contain a high density of voltage-gated Na\+ channels, allowing action potentials to be regenerated and propagate rapidly by saltatory conduction.

Question 10

A synaptic transmission involves the release of a neurocrine that acts on a postsynaptic cell to produce a slow, modulatory response. Which type of receptor is most likely involved?

Accepted Answer

Metabotropic receptor (G-protein coupled)

Question 11

Which of the following equations best describes the Nernst equation for the equilibrium potential of K\+?

Accepted Answer

$$E_K = \frac{RT}{zF} \ln \left( \frac{[K^+]_{out}}{[K^+]_{in}} \right)$$

Question 12

Which of the following is a characteristic of electrical synapses?

Accepted Answer

Ions flow directly from one cell to the next via gap junctions, allowing rapid communication.

Question 13

Which of the following best explains why myelinated axons conduct action potentials faster than unmyelinated axons?

Accepted Answer

Myelin increases membrane resistance and decreases current leak, allowing the depolarization to travel further between nodes.

Question 14

A neurocrine acts as a neurotransmitter at one synapse and as a neuromodulator at another. What determines its function at each site?

Accepted Answer

The type of receptor present on the postsynaptic cell.

Question 15

Which of the following best describes the effect of a neuromodulator acting through a metabotropic receptor?

Accepted Answer

It activates a G-protein, which can interact with ion channels or activate membrane-bound enzymes to produce a cellular response.

Question 16

Which of the following is TRUE regarding the refractory period of an action potential?

Accepted Answer

It prevents the backward propagation of the action potential along the axon.

Question 17

Which signal transduction pathway is activated by metabotropic receptors that interact with adenylyl cyclase?

Accepted Answer

cAMP pathway, which phosphorylates proteins to cause a cellular response.

Question 18

A neuron receives multiple synaptic inputs, some excitatory and some inhibitory. Which term best describes the process by which these inputs are integrated to determine if an action potential will be generated?

Accepted Answer

Summation

PreM #5 Neuronal Electrical Signaling and Cell-to-Cell Communication

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