BIO 360 - Exam 2 - Chapter 8 Review Questions

Question 1

List the three functional classes of neurons, and explain how they differ structurally and functionally.

Answer 1

Sensory afferents: carry messages from sensory receptors to CNS. Their cell bodies are located close to the CNS.

Interneurons: completely contained within the CNS and are often extensively branched.

Efferents: carry signals from the CNS to effectors. They have short, branched dendrites and long axons.

Question 2

Somatic motor neurons control ______ and ______ neurons control smooth and cardiac muscles, glands, and some adipose tissue.

Answer 2

skeletal muscles, autonomic

Question 3

Autonomic neurons are classified as either ______ or ______ neurons.

Answer 3

sympathetic or parasympathetic

Question 4

Match each term with its description:

axon
dendrite
afferent
efferent
trigger zone

process of a neuron that receives incoming signals
sensory neuron, transmits information to CNS
long process that transmits signals to the target cell
region of neuron where action potential begins
neuron that transmits information from CNS to the rest of the body

Answer 4

(a) axon: long process that transmits signals to the target cell

(b) dendrite: process of a neuron that receives incoming signals.

(c) afferent: sensory neuron, transmits information to CNS.

(d) efferent: neuron that transmits information from CNS to the rest of the body.

(e) trigger zone: region of neuron where action potential begins

Question 5

Name the two primary cell types found in the nervous system.

Answer 5

neurons and glial cells

Question 6

Draw a typical neuron and label the cell body, axon, dendrites, nucleus, trigger zone, axon hillock, collaterals, and axon terminals. Draw mitochondria, rough endoplasmic reticulum, Golgi complex, and vesicles in the appropriate sections of the neuron.

Answer 6

See Figs. 8.2 and 8.3.

Question 7

Axonal transport refers to the:

(a) release of neurotransmitters into the synaptic cleft.
(b) use of microtubules to send secretions from the cell body to the axon terminal.
(c) movement of organelles and cytoplasm up and down the axon.
(d) movement of the axon terminal to synapse with a new postsynaptic cell.
(e) none of these.

Answer 7

(c). Answer (b) is only partly correct because not all axonal transport uses microtubules and not all substances moved will be secreted.

Question 8

Match the numbers of the appropriate characteristics with the two types of potentials. Characteristics may apply to one or both types.

action potential
graded potential

(1) all-or-none
(2) can be summed
(3) amplitude decreases with distance
(4) exhibits a refractory period
(5) amplitude depends on strength of stimulus
(6) has no threshold

Answer 8

(a) 1, 4

(b) 2, 3, 5, 6

Question 9

Arrange the following events in the proper sequence:

Efferent neuron reaches threshold and fires an action potential.
Afferent neuron reaches threshold and fires an action potential.
Effector organ responds by performing output.
Integrating center reaches decision about response.
Sensory organ detects change in the environment.

Answer 9

(e) – (b) – (d) – (a) – (c)

Question 10

List the four major types of ion channels found in neurons. Arethey chemically gated, mechanically gated, or voltage-gated?

Answer 10

Na+ channels (voltage-gated along axon; any type of gating on dendrites); voltage-gated K+ channels along axon; voltage-gated Ca2+ channels in axon terminal; chemically gated Cl− channels

Question 11

Match the glial cell(s) on the right to the functions on the left. There may be more than one correct answer for each function.

modified immune cells
help form the blood-brain barrier
form myelin
separate CNS fluid compartments
found in peripheral nervous system
found in ganglia

astrocytes
ependymal cells
microglia
oligodendrocytes
satellite cells
Schwann cells

Answer 11

(a) 3; (b) 1; (c) 4, 6; (d) 2; (e) 5, 6; (f) 5

Question 12

An action potential is (circle all correct answers)

(a) a reversal of the Na+ and K+ concentrations inside and outside the neuron.
(b) the same size and shape at the beginning and end of the axon.
(c) initiated by inhibitory postsynaptic graded potentials.
(d) transmitted to the distal end of a neuron and causes release of neurotransmitter.

Answer 12

(b) and (d)

Question 13

Choose from the following ions to fill in the blanks correctly: Na+, K+, Ca2+, Cl-

(1) The resting cell membrane is more permeable to ______ than to ______.
(2) Although ______ contribute little to the resting membrane potential, they play a key role in generating electrical signals in excitable tissues.
(3) The concentration of ______is 12 times greater outside the cell than inside.
(4) The concentration of ______ is 30 times greater inside the cell than outside.
(5) An action potential occurs when ______ enter the cell.
The resting membrane potential is due to the high permeability of the cell.

Answer 13

(a) K+, Na+, Na+; (b) Na+; (c) K+; (d) Na+; (e) K+

Question 14

What is the myelin sheath?

Answer 14

insulating membranes around neurons that prevent current leak

Question 15

List two factors that enhance conduction speed.

Answer 15

larger axon diameter and the presence of myelin

Question 16

List three ways neurotransmitters are removed from the synapse.

Answer 16

enzymatic degradation, reabsorption, and diffusion

Question 17

Draw and label a graph of an action potential. Below the graph, draw the positioning of the K+ and Na+ channel gates during each phase.

Answer 17

See Figs. 8.8, 8.9, and 8.11.

Question 18

What causes the depolarization phase of an action potential? (Circle all that apply.)

(a) K+ leaving the cell through voltage-gated channels.

(b) K+ being pumped into the cell by the Na+-K+-ATPase.

(c) being pumped into the cell by the Na+-K+-ATPase.

(d) Na+ entering the cell through voltage-gated channels.

(e) opening of the Na+ channel inactivation gate.

Answer 18

(d)

Question 19

Name any four neurotransmitters, their receptor(s), and tell whether the receptor is an ion channel or a GPCR.

Answer 19

See Tbl. 8.4.

Question 20

Create a map showing the organization of the nervous system using the following terms, plus any terms you choose to add:

afferent signals
astrocyte
autonomic division
brain
CNS
efferent neuron
ependymal cell
glands
glial cells
integration
interneuron
microglia
muscles
neuron
neurotransmitter
oligodendrocyte
parasympathetic division
peripheral division
satellite cell
Schwann cell
sensory division
somatic motor division
spinal cord
stimulus
sympathetic division
target

Answer 20

See Figs. 8.1 and 8.4.

Question 21

Arrange the following terms to describe the sequence of events after a neurotransmitter binds to a receptor on a postsynaptic neuron. Terms may be used more than once or not at all.

(a) action potential fires at axon hillock
(b) trigger zone reaches threshold
(c) cell depolarizes
(d) exocytosis
(e) graded potential occurs
(f) ligand-gated ion channel opens
(g) local current flow occurs
(h) saltatory conduction occurs
(i) voltage-gated Ca2+ channels open
(j) voltage-gated K+ channels open
(k) voltage-gated Na+ channels open

Answer 21

(f) – (c) – (g) – (e) – (b) – (k) – (c) – (a) – (h) – (j) – (i) – (d)

Question 22

Match the best term (hyperpolarize, depolarize, repolarize) to the following events. The cell in question has a resting membrane potential of -70mV.

(a) membrane potential changes from -70mV to -50mV.

(b) membrane potential changes from -70mV to -90mV.

(c) membrane potential changes from +20mV to -60mV.

(d) membrane potential changes from -80mV to -70mV.

Answer 22

(a) depolarize, (b) hyperpolarize, (c) repolarize, (d) depolarize

Question 23

A neuron has a resting membrane potential of -70mV. Will the neuron hyperpolarize or depolarize when each of the following events occurs? (More than one answer may apply; list all those that are correct.)

(a) Na+ enters the cell

(b) K+ leaves the cell

(c) Cl- enters the cell

(d) Ca2+ enters the cell

Answer 23

(a) depolarize, (b) hyperpolarize, (c) hyperpolarize, (d) depolarize

Question 24

If all action potentials within a given neuron are identical, how does the neuron transmit information about the strength and duration of the stimulus?

Answer 24

Strength is coded by the frequency of action potentials; duration is coded by the duration of a train of repeated action potentials.

Question 25

The presence of myelin allows an axon to (choose all correct answers):
(a) produce more frequent action potentials.
(b) conduct impulses more rapidly.
(c) produce action potentials of larger amplitude.
(d) produce action potentials of longer duration.

Answer 25

(b)

Question 26

Define, compare, and contrast the following concepts:

(a) threshold, subthreshold, suprathreshold, all-or-none, overshoot, undershoot
(b) graded potential, EPSP, IPSP
(c) absolute refractory period, relative refractory period
(d) afferent neuron, efferent neuron, interneuron
(e) sensory neuron, somatic motor neuron, sympathetic neuron, autonomic neuron, parasympathetic neuron
(f) fast synaptic potential, slow synaptic potential
(g) temporal summation, spatial summation
(h) convergence, divergence

Answer 26

(a) Threshold signals trigger action potentials. Suprathreshold also trigger action potentials, but subthreshold do not unless summed. Action potentials are all-or-none events. Overshoot—portion of the action potential above 0 mV. Undershoot—after-hyperpolarization portion of the action potential. (b) Graded potentials may be depolarizing or hyperpolarizing. Graded potential in a postsynaptic cell is an EPSP if depolarizing and an IPSP if hyperpolarizing. (c) No stimulus can trigger another action potential during the absolute refractory period, but a suprathreshold stimulus can trigger an action potential during the relative refractory period. (d) See answer to question 1. (e) Sensory are afferents; all others are efferents. (f) Fast synaptic potentials result from neurotransmitters altering ion channel gating, occur rapidly, and are short-lived. Slow synaptic potentials are mediated through second messengers, may involve protein modification, and last longer. (g) Temporal summation—multiple stimuli arrive at the trigger zone close together in time. Spatial summation—multiple stimuli from different locations arrive simultaneously at the trigger zone. (h) Divergence—a single neuron branches and its collaterals synapse on multiple targets. Convergence—multiple presynaptic neurons provide input to a smaller number of postsynaptic neurons.

Question 27

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Answer 27

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Question 28

The voltage-gated Na+ channels of a neuron open when the neuron depolarizes. If depolarization opens the channels, what makes them close when the neuron is maximally depolarized?

Answer 28

Inactivation gates also respond to depolarization, but they close more slowly than the activation gates open, allowing ions to flow for a short period of time.

Question 29

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Answer 29

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Question 30

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Answer 30

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Question 31

An unmyelinated axon has a much greater requirement for ATP than a myelinated axon of the same diameter and length. Can you explain why?

Answer 31

Unmyelinated axons have many ion channels, so more ions cross during an action potential and must be returned to their original compartments by the Na+-K+-ATPase, using energy from ATP.

Question 32

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Answer 32

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Question 33

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Answer 33

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