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Ch. 11 Introduction to the Nervous System and Nervous Tissue
Chapter 11, Problem 11.7a

Fill in the blanks: The______is the period of time during which it is impossible to stimulate a neuron to have an action potential, whereas the______ is the period of time during which a larger-than-normal stimulus is required to elicit an action potential.

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Identify the two periods related to neuron action potentials: the absolute refractory period and the relative refractory period.
Understand that during the absolute refractory period, a neuron cannot be stimulated to fire another action potential, regardless of the strength of the stimulus.
Recognize that during the relative refractory period, a neuron can be stimulated to fire another action potential, but it requires a larger-than-normal stimulus.
Fill in the first blank with 'absolute refractory period' as it is the time when no action potential can be initiated.
Fill in the second blank with 'relative refractory period' as it is the time when a stronger stimulus is needed to initiate an action potential.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Absolute Refractory Period

The absolute refractory period is the time during which a neuron cannot generate another action potential, regardless of the strength of the stimulus. This occurs because the sodium channels are inactivated after an action potential, preventing any new depolarization. It ensures that action potentials are discrete events and helps maintain the unidirectional flow of signals along the neuron.
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Refractory Period

Relative Refractory Period

The relative refractory period follows the absolute refractory period and is the time during which a neuron can fire an action potential, but only if a stronger-than-normal stimulus is applied. During this phase, some sodium channels have returned to a resting state, but the neuron is still hyperpolarized due to the continued efflux of potassium ions. This period is crucial for regulating the frequency of action potentials.
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Refractory Period

Action Potential

An action potential is a rapid, temporary change in the membrane potential of a neuron, allowing it to transmit signals along its length. It is initiated when a neuron's membrane depolarizes past a certain threshold, leading to the opening of voltage-gated sodium channels. The action potential propagates down the axon, enabling communication between neurons and the transmission of information throughout the nervous system.
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Action Potential
Related Practice
Textbook Question

Albert, the patient in question 3, takes the drug lithium, which reduces the permeability of the neuronal axolemma to Na+ (that is, it allows fewer Na+ to enter the axon). Predict the effect this would normally have on his neuronal action potentials. Do you think this drug would be beneficial or harmful, considering his condition?

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Textbook Question

P​​redict the effect that tetrodotoxin would have on Albert's muscle fiber action potentials (see question 3). Would it affect end-plate potentials at the motor end plate? Why or why not? (Connects to Chapter 10)

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Textbook Question

Explain what would happen if depolarization of the trigger zone led to a negative feedback loop instead of a positive one. (Connects to Chapter 1)

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Textbook Question

Which of the following statements best describes saltatory conduction?


a. Every section of the axolemma must be depolarized and triggered to generate an action potential.

b. The internodes must generate action potentials.

c. The dendrites and cell bodies propagate EPSPs toward the trigger zone.

d. Only the nodes of Ranvier must generate action potentials.

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Textbook Question

Identify the following as properties of electrical synapses (ES), chemical synapses (CS), or both (B).           


a. ______The plasma membranes of presynaptic and postsynaptic neurons are joined by gap junctions.          

b. ______Transmission is unidirectional and delayed.          

c. ______A presynaptic neuron and a postsynaptic neuron are involved.          

d. ______The use of neurotransmitters packaged into synaptic vesicles is required.          

e. ______Transmission is nearly instantaneous and bidirectional.

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