Question 1

Tetrodotoxin (TTX), found in puffer fish, is a potent neurotoxin. What is its primary mechanism of action on neurons?

Accepted Answer

It blocks voltage-gated sodium channels, preventing the generation of action potentials.

Question 2

If a neuron’s membrane potential changes from -70 mV to -80 mV, which term best describes this change?

Accepted Answer

Hyperpolarization

Question 3

Which of the following best explains why graded potentials are decremental?

Accepted Answer

They lose strength due to passive current flow and leakage across the membrane.

Question 4

A patient eats shellfish during a red tide and develops paralysis. Which toxin is most likely responsible, and what is its effect?

Accepted Answer

Saxitoxin; it blocks voltage-gated sodium channels.

Question 5

Which of the following statements about action potentials is TRUE?

Accepted Answer

They are all-or-none and propagate without loss of strength.

Question 6

During the rapid depolarization phase of an action potential, which ion’s permeability increases most dramatically?

Accepted Answer

Sodium (Na+)

Question 7

What is the primary reason action potentials travel in only one direction along an axon?

Accepted Answer

The absolute refractory period prevents re-excitation of the region just fired.

Question 8

Which equation describes the decay of voltage during electrotonic conduction along an axon?

Accepted Answer

$$V_X = V_0$ e$$^{-X/\lambda}$$

Question 9

A local anesthetic like lidocaine is injected before a dental procedure. What is its effect at the cellular level?

Accepted Answer

It blocks voltage-gated sodium channels, preventing action potentials in sensory neurons.

Question 10

Which of the following best describes the difference between graded potentials and action potentials?

Accepted Answer

Graded potentials can summate; action potentials cannot.

Question 11

During the relative refractory period, what is required to generate a second action potential?

Accepted Answer

A stimulus stronger than threshold

Question 12

Which property of myelinated axons allows for faster conduction of action potentials compared to unmyelinated axons?

Accepted Answer

Saltatory conduction, where action potentials jump from node to node

Question 13

A neuron receives two stimuli close together in time at the same location, resulting in a larger depolarization. What is this phenomenon called?

Accepted Answer

Temporal summation

Question 14

Which of the following best explains why a subthreshold stimulus does NOT generate an action potential?

Accepted Answer

It does not open enough voltage-gated sodium channels to overcome potassium efflux.

Question 15

Which of the following is TRUE regarding the gating of voltage-gated sodium channels during an action potential?

Accepted Answer

Both activation and inactivation gates must be open for sodium to flow.

Question 16

What is the main effect of multiple sclerosis on action potential conduction?

Accepted Answer

It destroys myelin, slowing or blocking action potential propagation.

Question 17

Which of the following best describes the role of the sodium-potassium pump in maintaining the resting membrane potential?

Accepted Answer

It actively transports 3 Na+ out and 2 K+ in, maintaining the negative resting potential.

Question 18

Which of the following is a correct statement about the phases of an action potential?

Accepted Answer

During repolarization, potassium permeability increases and potassium exits the cell.

Question 19

How do action potentials encode the intensity of a stimulus?

Accepted Answer

By increasing the frequency of action potentials

Question 20

Which of the following best describes the effect of opening ligand-gated sodium channels on a postsynaptic neuron?

Accepted Answer

It causes a graded depolarization, possibly leading to an action potential if threshold is reached.

Electrical Signaling in Neurons: Graded and Action Potentials

Study Guide - Practice Questions