Question

A common feature of action potentials is that they

(A) cause the membrane to hyperpolarize and then depolarize.

(B) can undergo temporal and spatial summation.

(C) are triggered by a depolarization that reaches threshold.

(D) move at the same speed along all axons.

Short answer

(A) The statement“cause the membrane to hyperpolarize and then depolarize” is false.

(B) The statement “can undergo temporal and spatial summation” is false.

(C) The statement “are triggered by a depolarization that reaches threshold” is true.

(D) The statement “move at the same speed along all axons” is false.

Step-by-step solution

Action potential

The term action potential is the electrical signal used for the body’s neural signaling mechanism. It can be explained as the electrical form of information that can be transmitted across the different cells of the body via neurons.

Explanation of option ‘(A)’

An action potential is always accompanied by different electrical phases of the cell membrane, and it is generated in response to depolarization potential, after the propagation of the action potential to the next neuron or target cell, the initial cell experiences hyperpolarization.

Thus, depolarization occurs before action potential and hyperpolarization.

Therefore, the given statement is false.

Explanation of option ‘(B)

Spatial summation occurs when simultaneously occurring action potentials from nearby neurons are summed up in the target tissue, and temporal summation happens when multiple action potentials occurring at high frequency from a single neuron are summed up.

Thus, spatial and temporal summation are not features of an action potential.

Therefore, the given statement is false.

Explanation of option ‘(C)’

An incoming signal can be of varying strength, and depending on the strength, it causes different levels of membrane depolarization. When a signal is strong enough to produce enough positive potential and the membrane’s depolarization value reaches up to the threshold mark, it triggers the production of an action potential.

Thus, an action potential can only be triggered by a depolarization that reaches the membrane’s threshold value.

Therefore, the given statement is true.

Explanation of option ‘(D)’

The axonal fibers of neurons can either be myelinated or unmyelinated. This structural difference of the axons alters the speed at which action potentials travel across these fibers. Generally, the speed of action potential is comparatively faster in myelinated axons than in axons that are not myelinated.

Thus, the speed of action potential is not the same in all axonal fibers.

Therefore, the given statement is false.