Neuron Structure and Action Potential

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Questions and Answers

Which criterion is used to functionally classify neurons?

Functional classification groups neurons according to the direction in which the nerve impulse travels relative to the central nervous system.

Bipolar neurons are commonly ________.

found in the retina of the eye.

Collections of nerve cell bodies outside the central nervous system are called ________.

ganglia.

Cell bodies of sensory neurons may be located in ganglia lying outside the central nervous system.

True Signup and view all the answers

In myelinated axons, the voltage-regulated sodium channels are concentrated at the nodes of Ranvier.

True Signup and view all the answers

Which of the following statements is correct regarding the polarization of a neuronal membrane and the formation of a resting membrane potential?

Sodium/Potassium pumps maintain concentration gradients; sodium and potassium move down their concentration gradients through leakage channels. Signup and view all the answers

Which of the following does NOT describe conditions that occur during an action potential?

Na+ is used to repolarize the membrane. Signup and view all the answers

The interior surface of a neuron's plasma membrane at resting membrane potential will have a ________.

negative charge and contains less sodium than outside of the cell. Signup and view all the answers

Axon diameter and degree of myelination determine nerve impulse conduction velocity.

True Signup and view all the answers

Which choice best characterizes K+ leakage channels?

Transmembrane protein channels that are always open to allow K+ to cross the membrane without the additional input of energy. Signup and view all the answers

Assume you have a membrane with only potassium leakage channels. The RMP is -90mV. Predict the RMP if we add Na+ leakage channels. The most likely RMP value of Na+ is __________.

-70 mV. Signup and view all the answers

Complete the following sentence: The operation of the Na+−K+ ATPase pump __________.

The pumps move more Na+ than K+, which counteracts the effect of the membrane's being more permeable to K+. Signup and view all the answers

Cl− is a common, negatively charged extracellular ion. Predict the effect on the RMP if many Cl− gated channels are suddenly opened.

The cell would become more negative, leading to hyperpolarization. Signup and view all the answers

The membranes of neurons at rest are very permeable to _ but only slightly permeable to _.

more K+ moves out of the cell than Na+ moves into the cell. Signup and view all the answers

During depolarization, which gradient(s) move(s) Na+ into the cell?

A positive ion is driven into the cell because the inside of the cell is negative compared to the outside, and Na+ is driven in due to a greater concentration outside. Signup and view all the answers

The Na+-K+ pump actively transports both sodium and potassium ions across the membrane. In which direction is each ion pumped?

Na+ is pumped out of the cell against its electrochemical gradient and K+ is pumped into the cell against its concentration gradient. Signup and view all the answers

The concentrations of which two ions are highest outside the cell?

Both Na+ and Cl- are in higher concentrations outside the cell. Signup and view all the answers

During depolarization, the inside of the neuron's membrane becomes less negative.

True Signup and view all the answers

A postsynaptic potential is a graded potential that is the result of a neurotransmitter released into the synapse between two neurons.

True Signup and view all the answers

Where do most action potentials originate?

The first part of the axon is known as the initial segment, adjacent to the axon hillock. Signup and view all the answers

What opens first in response to a threshold stimulus?

The activation gates of voltage-gated Na+ channels open, and Na+ diffuses into the cytoplasm. Signup and view all the answers

What characterizes depolarization, the first phase of the action potential?

The plasma membrane, which was polarized to a negative value at the RMP, depolarizes to a positive value. Signup and view all the answers

What characterizes repolarization, the second phase of the action potential?

The plasma membrane must repolarize back to a negative value after being depolarized to a positive value. Signup and view all the answers

What event triggers the generation of an action potential?

The membrane potential must depolarize from -70 mV to -55 mV. Signup and view all the answers

What is the first change to occur in response to a threshold stimulus?

The activation gates of voltage-gated Na+ channels open very rapidly. Signup and view all the answers

What type of conduction takes place in unmyelinated axons?

An action potential is conducted continuously along an unmyelinated axon. Signup and view all the answers

An action potential is self-regenerating because __________.

The Na+ diffusing into the axon creates a depolarizing current that brings the next segment to threshold. Signup and view all the answers

Why does regeneration of the action potential occur in one direction?

At the peak of the depolarization phase, the inactivation gates close, making Na+ channels refractory. Signup and view all the answers

What is the function of the myelin sheath?

The myelin sheath increases the velocity of conduction by insulating the axon and reducing the loss of depolarizing current. Signup and view all the answers

What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?

Inactivation gates of Na+ channels close shortly after activation gates open, while K+ channels open. Signup and view all the answers

In which type of axon will the velocity of action potential conduction be the fastest?

In a large diameter axon with a myelin sheath. Signup and view all the answers

Which of the following events would be directly affected if a neuron had a mutation that prevented the production of voltage-gated Na+ channels?

Depolarization leading to action potentials. Signup and view all the answers

What type of event is required for an action potential to be generated?

The axolemma must be depolarized to threshold. Signup and view all the answers

You discover that a new chemical compound interacts with K+ voltage-dependent channels. What would be the effect on a neuron if the chemical came into contact with the axonal membrane?

The neuron would be unable to repolarize. Signup and view all the answers

If the neuron membrane becomes more permeable to Na+, what will happen?

Na+ will transport across the membrane, causing the cell to depolarize. Signup and view all the answers

Which of the following is a factor that determines the rate of impulse propagation?

The degree of myelination and axon diameter. Signup and view all the answers

In multiple sclerosis, the cells that are the target of an autoimmune attack are the ________.

Oligodendrocytes. Signup and view all the answers

Why does the injection of a local anesthetic into a finger still cause a loss of the sensation of touch?

Propagation of an action potential requires sequential opening of ion channels; interrupting this sequence results in numbness. Signup and view all the answers

Trigger zone

Area where nerve impulse is generated. Signup and view all the answers

Receptive region

Receives stimuli. Signup and view all the answers

Conducting region

Plasma membrane exhibits voltage-gated Na+ and K+ channels. Signup and view all the answers

Secretory region

Plasma membrane exhibits voltage-gated Ca2+ channels. Signup and view all the answers

Axon terminal

Releases neurotransmitters into the extracellular space. Signup and view all the answers

Receptive region (2)

Plasma membrane exhibits chemically gated ion channels. Signup and view all the answers

An action potential is regarded as an example of a positive feedback. Which example best illustrates this aspect?

A threshold stimulus causes the opening of voltage-gated Na+ channels. Signup and view all the answers

During the relative refractory period of an action potential, a larger than normal stimulus is needed. This is due to the fact that ________.

The voltage-gated potassium ion channels remain open long enough to hyperpolarize the axon membrane. Signup and view all the answers

What does the central nervous system use to determine the strength of a stimulus?

Frequency of action potentials. Signup and view all the answers

The period after an initial stimulus when a neuron is not sensitive to another stimulus is the ________.

absolute refractory period. Signup and view all the answers

Which ion channel opens in response to a change in membrane potential and participates in action potentials?

Voltage-gated channel. Signup and view all the answers

Saltatory conduction is made possible by ________.

the myelin sheath. Signup and view all the answers

Immediately after an action potential has peaked, which channels will open?

Voltage-gated potassium channels. Signup and view all the answers

A second nerve impulse cannot be generated until ________.

the membrane potential has been reestablished. Signup and view all the answers

The action potential is caused by permeability changes in the plasma membrane.

True Signup and view all the answers

If a postsynaptic neuron is stimulated to threshold by spatial summation, this implies that ________.

the postsynaptic cell has many synapses with many presynaptic neurons. Signup and view all the answers

If a postsynaptic cell is stimulated to threshold by temporal summation, this implies that ________.

a presynaptic neuron is sending frequent EPSP. Signup and view all the answers

An inhibitory postsynaptic potential (IPSP) is associated with ________.

hyperpolarization. Signup and view all the answers

Which of the following describes the excitatory postsynaptic potential?

Short distance depolarization. Signup and view all the answers

Which description of synapses is not correct?

All synaptic transmissions are indirect. Signup and view all the answers

In a lab, you are conducting tests with various chemicals. Frog muscle cells depolarize when you add nicotine to ACh receptors. What does this tell us?

The effect of a neurotransmitter is based on the properties of the receptor more than the neurotransmitter. Signup and view all the answers

When a neurotransmitter like GABA is acting in an inhibitory manner, which of the following is likely a result?

Hyperpolarization of the postsynaptic cell membrane. Signup and view all the answers

The effect of acetylcholine can be stimulating or inhibiting. Which explanation best describes this?

Different postsynaptic cells will have different receptors. Signup and view all the answers

Which of the following neurotransmitters is the principal inhibitory neurotransmitter of the spinal cord?

glycine. Signup and view all the answers

What component of the reflex arc determines the response to a stimulus?

The integration center receives sensory information, determines the response, and signals the appropriate effector(s). Signup and view all the answers

Study Notes

Neuron Classification and Structure

Neurons are functionally classified based on the direction of impulse relative to the CNS: sensory neurons (afferent), motor neurons (efferent), and interneurons (connecting neurons).
Bipolar neurons are primarily found in the retina of the eye.
Collections of nerve cell bodies outside the CNS are called ganglia.
Cell bodies of sensory neurons may be found in ganglia located outside the CNS.

Membrane Potential and Ion Channels

In myelinated axons, voltage-regulated sodium channels are concentrated at nodes of Ranvier.
The resting membrane potential (RMP) is maintained primarily by sodium/potassium pumps and leakage channels.
An action potential occurs when the membrane depolarizes from a threshold of -70 mV to -55 mV.
During depolarization, sodium (Na+) ions rush into the cell, leading to decreased negativity inside the membrane.

Action Potential Dynamics

Voltage-gated ion channels are essential for generating action potentials: Na+ channels open first, causing depolarization, followed by K+ channels during repolarization.
An action potential is self-regenerating due to the initial influx of Na+, which triggers further depolarization in adjacent segments.
Saltatory conduction skips between nodes of Ranvier in myelinated axons, increasing conduction velocity.

Refractory Periods and Stimulus Encoding

The absolute refractory period is when a neuron cannot generate another action potential regardless of stimulus strength.
During the relative refractory period, a stronger-than-normal stimulus can trigger another action potential because K+ channels may still be open.
The CNS determines stimulus strength via the frequency of action potentials, not their amplitude.

Synaptic Transmission

Postsynaptic potentials (PSPs) are graded potentials resulting from neurotransmitter binding at synapses, which can be either excitatory postsynaptic potentials (EPSPs) or inhibitory postsynaptic potentials (IPSPs).
Spatial summation occurs with multiple synapses from various presynaptic neurons; temporal summation involves multiple impulses from a single presynaptic neuron.
GABA, the principal inhibitory neurotransmitter in the spinal cord, leads to hyperpolarization.

Neurotransmitter Function

Neurotransmitter effects depend on the receptor type they bind to, exemplifying why acetylcholine can be excitatory or inhibitory.
Glycine primarily acts as an inhibitory neurotransmitter in the spinal cord.
The integration center in the reflex arc processes sensory input and generates the motor output response.

Anatomy of Neurons

The trigger zone, where action potentials originate, is located at the axon hillock.
Neuron membranes exhibit different regions: receptive (receives stimuli), conducting (has voltage-gated channels), secretory (releases neurotransmitters).
Local anesthetics block voltage-gated Na+ channels, inhibiting action potential propagation and sensory perception, even if mechanically gated channels remain functional.

By understanding these core concepts, students can grasp neuron functionality, action potential mechanisms, synaptic communication, and the overall organization of the nervous system.

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Test your knowledge on the classification and structure of neurons, as well as the dynamics of membrane potential and action potentials. This quiz covers sensory, motor, and interneurons, as well as the role of ion channels in generating action potentials.

Neuron Structure and Action Potential

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Questions and Answers

Which criterion is used to functionally classify neurons?

Bipolar neurons are commonly ________.

Collections of nerve cell bodies outside the central nervous system are called ________.

Cell bodies of sensory neurons may be located in ganglia lying outside the central nervous system.

In myelinated axons, the voltage-regulated sodium channels are concentrated at the nodes of Ranvier.

Which of the following statements is correct regarding the polarization of a neuronal membrane and the formation of a resting membrane potential?

Which of the following does NOT describe conditions that occur during an action potential?

The interior surface of a neuron's plasma membrane at resting membrane potential will have a ________.

Axon diameter and degree of myelination determine nerve impulse conduction velocity.

Which choice best characterizes K+ leakage channels?

Assume you have a membrane with only potassium leakage channels. The RMP is -90mV. Predict the RMP if we add Na+ leakage channels. The most likely RMP value of Na+ is __________.

Complete the following sentence: The operation of the Na+−K+ ATPase pump __________.

Cl− is a common, negatively charged extracellular ion. Predict the effect on the RMP if many Cl− gated channels are suddenly opened.

The membranes of neurons at rest are very permeable to _____ but only slightly permeable to _____.

During depolarization, which gradient(s) move(s) Na+ into the cell?

The Na+-K+ pump actively transports both sodium and potassium ions across the membrane. In which direction is each ion pumped?

The concentrations of which two ions are highest outside the cell?

During depolarization, the inside of the neuron's membrane becomes less negative.

A postsynaptic potential is a graded potential that is the result of a neurotransmitter released into the synapse between two neurons.

Where do most action potentials originate?

What opens first in response to a threshold stimulus?

What characterizes depolarization, the first phase of the action potential?

What characterizes repolarization, the second phase of the action potential?

What event triggers the generation of an action potential?

What is the first change to occur in response to a threshold stimulus?

What type of conduction takes place in unmyelinated axons?

An action potential is self-regenerating because __________.

Why does regeneration of the action potential occur in one direction?

What is the function of the myelin sheath?

What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?

In which type of axon will the velocity of action potential conduction be the fastest?

Which of the following events would be directly affected if a neuron had a mutation that prevented the production of voltage-gated Na+ channels?

What type of event is required for an action potential to be generated?

You discover that a new chemical compound interacts with K+ voltage-dependent channels. What would be the effect on a neuron if the chemical came into contact with the axonal membrane?

If the neuron membrane becomes more permeable to Na+, what will happen?

Which of the following is a factor that determines the rate of impulse propagation?

In multiple sclerosis, the cells that are the target of an autoimmune attack are the ________.

Why does the injection of a local anesthetic into a finger still cause a loss of the sensation of touch?

Trigger zone

Receptive region

Conducting region

Secretory region

Axon terminal

Receptive region (2)

An action potential is regarded as an example of a positive feedback. Which example best illustrates this aspect?

During the relative refractory period of an action potential, a larger than normal stimulus is needed. This is due to the fact that ________.

What does the central nervous system use to determine the strength of a stimulus?

The period after an initial stimulus when a neuron is not sensitive to another stimulus is the ________.

Which ion channel opens in response to a change in membrane potential and participates in action potentials?

Saltatory conduction is made possible by ________.

Immediately after an action potential has peaked, which channels will open?

A second nerve impulse cannot be generated until ________.

The action potential is caused by permeability changes in the plasma membrane.

If a postsynaptic neuron is stimulated to threshold by spatial summation, this implies that ________.

If a postsynaptic cell is stimulated to threshold by temporal summation, this implies that ________.

An inhibitory postsynaptic potential (IPSP) is associated with ________.

Which of the following describes the excitatory postsynaptic potential?

Which description of synapses is not correct?

In a lab, you are conducting tests with various chemicals. Frog muscle cells depolarize when you add nicotine to ACh receptors. What does this tell us?

When a neurotransmitter like GABA is acting in an inhibitory manner, which of the following is likely a result?

The effect of acetylcholine can be stimulating or inhibiting. Which explanation best describes this?

Which of the following neurotransmitters is the principal inhibitory neurotransmitter of the spinal cord?

What component of the reflex arc determines the response to a stimulus?

Study Notes

Neuron Classification and Structure

Membrane Potential and Ion Channels

Action Potential Dynamics

Refractory Periods and Stimulus Encoding

Synaptic Transmission

Neurotransmitter Function

Anatomy of Neurons

Studying That Suits You

Description

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