Chapter 11

Question 1

Cold sores on the skin of the mouth occur when herpes simplex viruses that are dormant in neural ganglia become active and travel to the skin of the mouth. Which of the following is the mechanism by which these viruses travel from the ganglia (located within the head) to the skin of the mouth?

Answer 1

anterograde axonal transport

Question 2

Where in the neuron is an action potential initially generated?

Answer 2

axon hillock

Question 3

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

Answer 3

voltage-gated Na+ channels

Question 4

The repolarization phase of an action potential results from __________.

Answer 4

the opening of voltage-gated K+ channels

Question 5

Hyperpolarization results from __________.

Answer 5

slow closing of voltage-gated K+ channels

Question 6

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

Answer 6

100 mV

Question 7

What type of conduction takes place in unmyelinated axons?

Answer 7

Continuous conduction

Question 8

An action potential is self-regenerating because __________.

Answer 8

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

Question 9

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

Answer 9

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

Question 10

What is the function of the myelin sheath?

Answer 10

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

Question 11

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

Answer 11

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

Question 12

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

Answer 12

Myelinated axons with the largest diameter

Question 13

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

Answer 13

K+; Na+

Question 14

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

Answer 14

both the electrical and chemical gradients

Question 15

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

Answer 15

–70 mV

Question 16

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?

Answer 16

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

Question 17

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

Answer 17

Na+ and Cl–

Question 18

Local anesthetics block voltage-gated Na+ channels, but they do not block mechanically gated ion channels. Sensory receptors for touch (and pressure) respond to physical deformation of the receptors, resulting in the opening of specific mechanically gated ion channels. Why does injection of a local anesthetic into a finger still cause a loss of the sensation of touch from the finger?

Answer 18

Touch stimulation of this sensory receptor will open the mechanically gated ion channels, but action potentials are still not initiated because propagation of an action potential requires the opening of voltage-gated Na+ channels.

Question 19

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

Answer 19

synaptic cleft.

Question 20

A molecule that carries information across a synaptic cleft is a

Answer 20

neurotransmitter.

Question 21

When calcium ions enter the synaptic terminal,

Answer 21

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

Question 22

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

Answer 22

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

Question 23

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

Answer 23

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

Question 24

Which membrane potential occurs because of the influx of Na+ through chemically gated channels in the receptive region of a neuron?

Answer 24

excitatory postsynaptic potential

Question 25

Which neurotransmitter(s) is/are the body’s natural pain killer?

Answer 25

endorphins

Question 26

Which neuron circuit pattern is involved in the control of rhythmic activities such as breathing?

Answer 26

reverberating circuit

Question 27

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

Answer 27

integration center