Appendix H
Answers
A-23
APPENDIX H
ANSWERS
negative (hyperpolarize). When hyperpolarized, the cell is farther from
its threshold potential and so is less likely to produce an action potential.
Chapter 12
Check Your Understanding 1.
Te third ventricle is surrounded by the
diencephalon.
2.
Te cerebral hemispheres and the cerebellum have an
outside layer of gray matter in addition to central gray matter and its
surrounding white matter.
3.
Convolutions increase surface area of the
cortex, which allows more neurons to occupy the limited space within
the skull.
4.
Te central sulcus separates primary motor areas from so-
matosensory areas.
5.
Motor functions on the leF side of the body are
controlled by the right hemisphere of the brain because motor tracts from
the right hemisphere cross over (in the medulla oblongata) to the leF side
of the spinal cord to go to the leF side of the body.
6.
Commissural fibers
(which form commissures) allow the cerebral hemispheres to “talk to each
other.”
7.
Te caudate nucleus, putamen, and globus pallidus together
form the basal nuclei.
8.
Virtually all inputs ascending to the cerebral
cortex synapse in the thalamus en route.
9.
Te hypothalamus oversees
the autonomic nervous system.
10.
Te pyramids of the medulla are the
corticospinal (pyramidal) tracts, the large voluntary motor tracts descend-
ing from the motor cortex. Te result of decussation (crossing over) is that
each side of the motor cortex controls the opposite side of the body.
11.
Te cerebral peduncles and the colliculi are associated with the mid-
brain.
12.
Tere are many possible answers to this question—here are a
few: Structurally, the cerebellum and cerebrum are similar in that they
both have a thin outer cortex of gray matter, internal white matter, and
deep gray matter nuclei. Also, both have body maps (homunculi) and
large fiber tracts connecting them to the brain stem. Both receive sen-
sory input and influence motor output. A major difference is that the
cerebellum is almost entirely concerned with motor output, whereas the
cerebrum has much broader responsibilities. Also, while a cerebral hemi-
sphere controls the opposite side of the body, a cerebellar hemisphere
controls the same side of the body.
13.
Te hypothalamus is part of the
limbic system and also an autonomic (visceral) control center.
14.
±aylor
is increasing the amount of sensory stimuli she receives, which will be
relayed to the reticular activating system, which, in turn, will increase
activation of the cerebral cortex.
15.
Delta waves are typically seen in deep
sleep in normal adults.
16.
Drowsiness (or lethargy) and stupor are stages
of consciousness between alertness and coma.
17.
Most skeletal muscles
are actively inhibited during REM sleep.
18.
±ransfer of memory from
S±M to L±M is enhanced by (1) rehearsal, (2) association (tying “new” in-
formation to “old” information), and (3) a heightened emotional state (for
example, alert, motivated, surprised, or aroused).
19.
Te basal nuclei and
premotor cortex are involved in procedural (skills) memory, but not in
declarative memory.
20.
CS², formed by the choroid plexuses as a filtrate
of blood plasma, is a watery “broth” similar in composition to plasma. It
protects the brain and spinal cord from blows and other trauma, helps
nourish the brain, and carries chemical signals from one part of the brain
to another.
21.
A ±IA is a temporary loss of blood supply to brain tissue,
and it differs from a stroke in that the resultant impairment is fully revers-
ible.
22.
Mrs. Lee might have Parkinson’s disease.
23.
Te nerves serving
the limbs arise in the cervical and lumbar enlargements of the spinal cord.
24.
In the spinothalamic pathway, the cell bodies of first-order sensory
neurons are outside the spinal cord in a ganglion, cell bodies of second-
order sensory neurons are in the dorsal horn of the spinal cord, and cell
bodies of third-order sensory neurons are in the thalamus. (See also ²ig-
ure 12.31b.)
25.
A loss of motor function is called paralysis. Lower limb
paralysis could be caused by a spinal cord injury in the thoracic region
(between ±
1
and L
1
). If the spinal cord is transected, the result is paraple-
gia. If the cord is only bruised, he may regain function in the limbs. An
MRI scan (or C± scan) of the spinal cord would be helpful.
26.
Alar plate
neuroblasts become interneurons, whereas basal plate neuroblasts become
5.
A nerve fiber is a long axon, an extension of the cell. In connective tis-
sue, fibers are extracellular proteins that provide support. In muscle tissue,
a muscle fiber is a muscle cell.
6.
A nucleus within the brain is a cluster of
cell bodies, whereas the nucleus within each neuron is a large organelle
that acts as the control center of the cell.
7.
In the CNS, a myelin sheath is
formed by oligodendrocytes that wrap their plasma membranes around
the axon. Te myelin sheath protects and electrically insulates axons and
increases the speed of transmission of nerve impulses.
8.
Burning a finger
will first activate unipolar (pseudounipolar) neurons that are sensory
(afferent) neurons. Te impulse to move your finger away from the heat
will be carried by multipolar neurons that are motor (efferent) neurons.
9.
Te concentration gradient and the electrical gradient—together called
the electrochemical gradient—determine the direction in which ions flow
through an open membrane channel.
10.
Tere is more leakage of K
1
than of any other cations.
11.
Action potentials are larger than graded
potentials and travel further. Graded potentials generally initiate action
potentials.
12.
An action potential is regenerated anew at each membrane
patch.
13.
Conduction of action potentials is faster in myelinated axons
because myelin allows the axon membrane between myelin sheath gaps
to change its voltage rapidly, and allows current to flow only at the widely
spaced gaps.
14.
If a second stimulus occurs before the end of the absolute
refractory period, no AP can occur because sodium channels are still inac-
tivated.
15.
At an electrical synapse, neurons are joined by gap junctions.
16.
Voltage-gated ion (Ca
2
1
) channels are found in the presynaptic axon
terminal and open when an action potential reaches the axon terminal.
Chemically gated ion channels are found in the postsynaptic membrane
and open when neurotransmitter binds to the receptor protein.
17.
IPSPs
result from the flow of either K
1
or Cl
2
through chemically gated chan-
nels. EPSPs result from the flow of both Na
1
and K
1
through chemically
gated channels.
18.
±emporal summation is summation in time of graded
potentials occurring in quick succession at the postsynaptic membrane. It
can result from EPSPs arising from just one synapse. Spatial summation
is summation in space—a postsynaptic neuron is stimulated by a large
number of terminals at the same time.
19.
ACh interacts with more than
one specific receptor type, and this explains how it can excite at some
synapses and inhibit at others.
20.
cAMP is called a second messenger
because it relays the message between the first messenger (the original
chemical messenger) outside of the cell and effector molecules that will
ultimately bring about the desired response within the cell.
21.
Reverber-
ating circuits and parallel aFer-discharge circuits both result in prolonged
output.
22.
Te pattern of neural processing is serial processing. Te
response is a reflex arc.
23.
Te pattern of neural processing is parallel
processing.
24.
Te growing tip of an axon is called a growth cone. Neuro-
tropins are chemicals that signal the growth cone.
Review Questions 1.
b;
2.
(1)d, (2)b, (3)f, (4)c, (5)a;
3.
b;
4.
c;
5.
a;
6.
c;
7.
b;
8.
d;
9.
c;
10.
c;
11.
a;
12.
(1)d, (2)b, (3)a, (4)c
Case Study 1.
Te electrical signals generated by neurons are called
ac-
tion potentials
. An action potential is a change in membrane potential
that involves depolarization and repolarization phases.
2.
An inhibitory
postsynaptic potential (IPSP) is a signal that makes it less likely that a
postsynaptic neuron will be able to generate an action potential. Tis
effect is usually produced when the signal causes the membrane poten-
tial of the postsynaptic neuron to become more negative, moving away
from the axon’s threshold potential.
3.
GABA falls into the amino acid
class of neurotransmitters. Tis same class includes glycine, glutamate,
and aspartate.
4.
±o enhance the actions of GABA at a synapse, a drug
could either (1) act presynaptically to increase the release of GABA at the
synapse, (2) decrease the reuptake of GABA aFer it has been released, or
(3) act postsynaptically to either increase the binding strength of GABA
at its receptors, or increase the number of receptors.
5.
An influx of Cl
2
into the postsynaptic cell causes the membrane potential to become more
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