CH 12 HW

What is the typical duration of a nerve action potential?

2 ms

Compared to type A axons, type C axons are __________. -unmyelinated -smaller diameter -slower propagating -All of the listed responses are correct.

All of the listed responses are correct

During propagation of the action potential, __________. -local currents depolarize a spot adjacent to the active zone -after threshold is reached, voltage-gated sodium channels open rapidly -the axon hillock depolarizes the initial segment -All of the listed responses are correct.

All of the listed responses are correct.

How is an action potential propagated along an axon?

An influx of sodium ions from the current action potential depolarizes the adjacent area.

Which letter shows when the axon membrane has become hyperpolarized?

B

What type of conduction takes place in unmyelinated axons?

Continuous conduction

In which cell does a graded potential occur?

Graded potentials occur in all the cell types listed.

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

Inactivation gates of voltage-gated Na+‎ channels close, while activation gates of voltage-gated K+‎ channels open.

Where do most action potentials originate?

Initial segment

The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors.

The presence of concentration gradients and leak channels

Typical CNS neurons are amitotic due to the absence of what structure?

centrioles

Leak channels allow the movement of potassium and sodium ions by what type of membrane transport?

channel-mediated diffusion

Which type of ion channel is always open?

leak

Neuroglia perform all of these functions EXCEPT __________.

release neurotransmitters

The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________.

saltatory propagation

In a neuron, sodium and potassium concentrations are maintained by the sodium-potassium exchange pump such that __________.

the sodium concentration is higher outside the cell than inside the cell and the potassium concentration is higher inside the cell than outside the cell.

An action potential releases neurotransmitter from a neuron by opening which of the following channels?

voltage-gated Ca2+ channels

The depolarization phase of an action potential results from the opening of which channels?

voltage-gated Na+ channels

What is primarily responsible for the brief hyperpolarization near the end of the action potential?

voltage-gated potassium channels taking some time to close in response to the negative membrane potential

In a typical neuron, what is the equilibrium potential for sodium?

+66mV

Around what transmembrane potential does threshold commonly occur?

-60 mV

The sodium-potassium exchange pump stabilizes resting potential of the neuron membrane at about __________.

-70 mV

What is the value for the resting membrane potential for most neurons?

-70 mV

Approximately how fast do action potentials propagate in unmyelinated axons in humans?

1 meter per second

What is the magnitude (amplitude) of an action potential?

100 mV

In a typical neuron, what is the equilibrium potential for potassium?

90 mV

What ion causes repolarization of the neuron during an action potential?

K+ (potassium)

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

K+; Na+

Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?

Leak channels

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

Myelinated axons with the largest diameter

What ion is responsible for the depolarization of the neuron during an action potential?

Na+ (sodium)

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

Na+ and Cl-

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

Na+ is pumped out of the cell and K+ is pumped into the cell.

What prevents the Na+ and K+ gradients from dissipating?

Na+-K+ ATPase

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

Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.

Identify the chemical or molecule at the end of the arrow.

Potassium ion

How do action potential propagation speeds in myelinated and unmyelinated axons compare?

Propagation is faster in myelinated axons.

Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference?

Resting membrane potential (RMP)

Sodium ions are transported out of the cell. Potassium ions are transported into the cell.

Sodium ions are transported out of the cell. Potassium ions are transported into the cell.

Why does the action potential only move away from the cell body?

The areas that have had the action potential are refractory to a new action potential.

Why does regeneration of the action potential occur in one direction, rather than in two directions?

The inactivation gates of voltage-gated Na+‎ channels close in the node, or segment, that has just fired an action potential.

On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?

The inside surface of the plasma membrane is much more negatively charged than the outside surface

Josh and a bunch of friends decided to see how many people they could squeeze into a small car for a charity event. Once inside, Josh felt it get hot, smelly, and like the air was getting squished out of his lungs. He also noticed aches and pains in his joints. Which of the following statements best describes the type of sensory neurons involved?

The interoceptors, exteroceptors, and proprioceptors were all monitoring his condition.

At rest, why is the transmembrane potential of a neuron (-70 mV) closer to the potassium equilibrium potential (-90 mV) than it is to the sodium equilibrium potential (+66 mV)?

The membrane is much more permeable to potassium ions than to sodium ions.

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

The membrane potential changes from a negative value to a positive value.

What event triggers the generation of an action potential?

The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.

What is the function of the myelin sheath?

The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.

In an unmyelinated axon, why doesn't the action potential suddenly "double back" and start propagating in the opposite direction?

The previous axonal segment is refractory.

The plasma membrane is much more permeable to K+ than to Na+. Why?

There are many more K+ leak channels than Na+ leak channels in the plasma membrane.

What opens first in response to a threshold stimulus?

Voltage-gated Na+ channels

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

Voltage-gated Na+ channels change shape, and their activation gates open.

During an action potential, after the membrane potential reaches +30 mV, which event(s) primarily affect(s) the membrane potential?

Voltage-gated sodium channels begin to inactivate (close) and voltage-gated potassium channels begin to

What happens just after an axon is depolarized to threshold?

Voltage-gated sodium channels open.

Multiple sclerosis (MS) is a disease that stops action potential propagation by destroying the myelin around (normally) myelinated axons. Which of the following best describes how MS stops action potential propagation?

Without myelin, the internode membrane resistance decreases, preventing local currents from reaching adjacent nodes.

The electrochemical gradient for potassium ions when the transmembrane potential is at the resting potential (-70 mV) is caused by what?

a chemical gradient going out of the cell and an electrical gradient going into the cell

The velocity of the action potential is fastest in which of the following axons?

a small myelinated axon

The mechanism by which the neurotransmitter is returned to a presynaptic neuron's axon terminal is specific for each neurotransmitter. Which of the following neurotransmitters is broken down by an enzyme before being returned?

acetylcholine

Which division of the PNS would contain sensory nerve fibers from special sensory receptors?

afferent

Which cell is indicated by the arrow?

astrocyte

When a person has a stroke, blood leaks into the brain tissue. Which type of neuroglia cells would make structural repairs to the damage?

astrocytes

Where are action potentials regenerated as they propagate along an unmyelinated axon?

at every segment of the axon

Where are action potentials regenerated as they propagate along a myelinated axon?

at the nodes

Where in the neuron is an action potential initially generated?

axon hillock

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

both the electrical and chemical gradients

The afferent division of the PNS __________

carries sensory information

The electrochemical gradient for sodium ions in a neuron when the transmembrane potential is at the resting potential is caused by what?

chemical and electrical gradients both going into the cell

Binding of a neurotransmitter to its receptors opens __________ channels on the __________ membrane.

chemically gated; postsynaptic

In order to communicate with multiple cells at the same time, an axon may branch along its length, producing side branches called __________.

collaterals

An action potential is self-regenerating because __________.

depolarizing currents established by the influx of Na+‎ flow down the axon and trigger an action potential at the next segment

Binding of the neurotransmitter to its receptor causes the membrane to __________.

either depolarize or hyperpolarize

What type of membrane transport causes the depolarization phase of the action potential in neurons?

facilitated diffusion

In contrast to the internodes of a myelinated axon, the nodes __________.

have lower membrane resistance to ion movement

Compared to the electrical gradient for sodium at rest, the electrical gradient for potassium at rest is __________.

in the same direction and of the same magnitude.

Action potential propagation begins (is first generated at) what region of a neuron?

initial segment

In what part of the neuron does the action potential typically initiate?

initial segment of the axon

When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron,

ion channels in the plasma membrane of the receiving neuron open.

Which cell is indicated by the arrow?

microglial

Most CNS neurons fall into which structural category?

multipolar

A molecule that carries information across a synaptic cleft is a

neurotransmitter.

What is this structure of the neural cell?

nucleus

Which cell is indicated by the arrow?

oligodendrocyte

What causes repolarization of the membrane potential during the action potential of a neuron?

potassium efflux (leaving the cell)

The most abundant intracellular cation is __________, while the most abundant extracellular anion is __________.

potassium, chloride

In a synapse, neurotransmitters are stored in vesicles located in the __________.

presynaptic neuron

Which of these types of neuroglia are abundant in peripheral ganglia?

satellite cells

Hyperpolarization results from __________.

slow closing of voltage-gated K+ channels

The movement of what ion is responsible for the local currents that depolarize other regions of the axon to threshold?

sodium (Na+)

The small space between the sending neuron and the receiving neuron is the

synaptic cleft.

What is this structure of the neural cell?

synaptic terminals

The repolarization phase of an action potential results from __________.

the opening of voltage-gated K+ channels

If a signal from a sending neuron makes the receiving neuron more negative inside,

the receiving neuron is less likely to generate an action potential.

What is the electrochemical gradient of an ion?

the sum of the electrical and chemical gradients for that ion

During an action potential of a neuron, what directly causes the different channels to open and close?

the transmembrane potential (voltage)

When calcium ions enter the synaptic terminal,

they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.