Neuronal Signaling and the Structure of the Nervous System
189
Chapter 6 Test Questions
(Answers appear in Appendix A.)
1. Which best describes an afferent neuron?
a. The cell body is in the central nervous system and the
peripheral axon terminal is in the skin.
b. The cell body is in the dorsal root ganglion and the central
axon terminal is in the spinal cord.
c. The cell body is in the ventral horn of the spinal cord and
the axon ends on skeletal muscle.
d. The dendrites are in the peripheral nervous system and the
axon terminal is in the dorsal root.
e. All parts of the cell are within the central nervous
system.
2. Which incorrectly pairs a glial cell type with an associated
function?
a. astrocytes; formation of the blood-brain barrier
b. microglia; performance of immune function in the central
nervous system
c. oligodendrocytes; formation of myelin sheaths on axons in
the peripheral nervous system
d. ependymal cells; regulation of production of cerebrospinal
uid
e. astrocytes; removal of potassium ions and neurotransmitters
from the brain’s extracellular fl
uid
3. If the extracellular chloride concentration is 110 mmol/L,
and a particular neuron maintains an intracellular chloride
concentration of 4 mmol/L, at what membrane potential
would chloride be closest to electrochemical equilibrium in
that cell?
a. +80 mV
b. +60 mV
c. 0 mV
d. –86 mV
e. –100 mV
4. Consider the fi ve experiments below, in which the concentration
gradient for sodium was varied. In which case(s) would sodium
tend to leak out of the cell if the membrane potential was
experimentally held at +42 mV?
Experiment
Extracellular
Na
+
(mmol/L)
Intracellular
Na
+
(mmol/L)
A
50
15
B
60
15
C
70
15
D
80
15
E
90
15
a. A only
b. B only
c. C only
d. A, B, and C
e. D and E
5. Which is a true statement about the resting membrane potential
in a typical neuron?
a. The membrane potential is closer to the sodium equilibrium
potential than to the potassium equilibrium potential.
b. The chloride permeability is higher than that for sodium or
potassium.
c. The membrane potential is at the equilibrium potential for
potassium.
d. There is no ion movement at the steady resting membrane
potential.
e. Ion movement by the Na
+
/K
+
-ATPase pump is equal and
opposite to the leak of ions through sodium and potassium
channels.
6. If a ligand-gated channel permeable to both sodium and
potassium was briefl y opened at a specifi c location on the
membrane of a typical resting neuron, what would result?
a. Local currents on the inside of the membrane would fl ow
away from that region.
b. Local currents on the outside of the membrane would fl ow
away from that region.
c. Local currents would travel without decrement all along the
cell’s length.
d. A brief local hyperpolarization of the membrane would result.
e. Fluxes of sodium and potassium would be equal, so no local
currents would fl ow.
7. Which ion channel state correctly describes the phase of the
action potential it is associated with?
a. Voltage-gated sodium channels are inactivated in a resting
neuronal membrane.
b. Open voltage-gated potassium channels cause the
depolarizing upstroke of the action potential.
c. Open voltage-gated potassium channels cause
afterhyperpolarization.
d. The sizable leak through voltage-gated potassium channels
determines the value of the resting membrane potential.
e. Opening of voltage-gated chloride channels is the main
factor causing rapid repolarization of the membrane at the
end of an action potential.
8. Two neurons, A and B, synapse onto a third neuron, C.
If neurotransmitter from A opens ligand-gated channels
permeable to sodium and potassium, while neurotransmitter
from B opens ligand-gated chloride channels, which of the
following statements is true?
a. An action potential in neuron A causes a depolarizing EPSP
in neuron B.
b. An action potential in neuron B causes a depolarizing EPSP
in neuron C.
c. Simultaneous action potentials in A and B will cause
hyperpolarization of neuron C.
d. Simultaneous action potentials in A and B will cause less
depolarization of neuron C than if only neuron A fi red an
action potential.
e. An action potential in neuron B will bring neuron C closer
to its action potential threshold than would an action
potential in neuron A.
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