Ch. 48 - Neurons, Synapses, and Signaling

Campbell - Campbell Biology 11th Edition

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Urry 11th Edition

Ch. 48 - Neurons, Synapses, and Signaling

Problem 4

Chapter 48, Problem 4

Why are action potentials usually conducted in one direction?
a. Ions can flow along the axon in only one direction
b. The brief refractory period prevents the reopening of voltage-gated Na⁺ channels
c. The axon hillock has a higher membrane potential than the terminals of the axon
d. Voltage-gated channels for both Na⁺ and K⁺ open in only one direction.

Verified step by step guidance

Understand the concept of action potentials: Action potentials are rapid electrical signals that travel along the axon of a neuron, allowing communication between neurons.

Learn about the refractory period: After an action potential occurs, there is a brief period during which the neuron is unable to fire another action potential. This is known as the refractory period.

Explore the role of voltage-gated Na+ channels: During the refractory period, the voltage-gated Na+ channels are temporarily inactivated, preventing the initiation of another action potential in the same region.

Consider the directionality of action potential conduction: Due to the refractory period, the action potential cannot travel backward because the Na+ channels behind the action potential are inactivated, ensuring one-way conduction.

Evaluate the options: Option b is correct because the brief refractory period prevents reopening of voltage-gated Na+ channels, ensuring that action potentials are conducted in one direction.

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Key Concepts

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

Action Potential

An action potential is a rapid rise and subsequent fall in voltage or membrane potential across a cellular membrane, primarily in neurons. It is initiated when a neuron sends information down an axon, away from the cell body, and involves the opening and closing of ion channels, particularly sodium (Na+) and potassium (K+) channels.

Refractory Period

The refractory period is a short time after an action potential during which a neuron is unable to fire another action potential. This period is divided into the absolute refractory period, where no new action potential can be initiated, and the relative refractory period, where a stronger-than-normal stimulus is required. It ensures unidirectional propagation of the action potential along the axon.

Voltage-Gated Ion Channels

Voltage-gated ion channels are proteins in the cell membrane that open or close in response to changes in membrane potential. These channels are crucial for the generation and propagation of action potentials, as they allow the selective flow of ions like Na+ and K+, which alters the membrane potential and facilitates the transmission of electrical signals along neurons.

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Related Practice

Textbook Question

Where are neurotransmitter receptors located?

a. The nuclear membrane

b. The nodes of Ranvier

c. The postsynaptic membrane

d. Synaptic vesicle membranes

Textbook Question

Suppose a particular neurotransmitter causes an IPSP in postsynaptic cell X and an EPSP in postsynaptic cell Y. A likely explanation is that

a. The threshold value in the postsynaptic membrane is different for cell X and cell Y

b. The axon of cell X is myelinated, but that of cell Y is not

c. Only cell Y produces an enzyme that terminates the activity of the neurotransmitter

d. Cells X and Y express different receptor molecules for this particular neurotransmitter

Textbook Question

Which of the following is the most direct result of depolarizing the presynaptic membrane of an axon terminal?

a. Voltage-gated calcium channels in the membrane open

b. Synaptic vesicles fuse with the membrane

c. Ligand-gated channels open, allowing neurotransmitters to enter the synaptic cleft

d. An EPSP or IPSP is generated in the postsynaptic cell

Textbook 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

Textbook Question

What happens when a resting neuron's membrane depolarizes?

a. There is a net diffusion of Na⁺ out of the cell

b. The equilibrium potential for K⁺ (Eₖ) becomes more positive

c. The neuron's membrane voltage becomes more positive

d. The cell's inside is more negative than the outside

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