Chapter 12
The Central Nervous System
449
12
(ah-mig
9
dah-loid), an almond-shaped nucleus that sits on the
tail of the caudate nucleus, and other parts of the rhinencephalon
(
cingulate gyrus
,
septal nuclei
, the C-shaped
hippocampus
,
dentate
gyrus
, and
parahippocampal gyrus
). In the diencephalon, the main
limbic structures are the
hypothalamus
and the
anterior thalamic
nuclei
. Te
fornix
(“arch”) and other fiber tracts link these limbic
system regions together.
Te limbic system is our
emotional
, or
affective
(feelings),
brain
. Te amygdaloid body and the anterior part of the
cingulate gyrus
seem especially important in emotions. Te
amygdaloid body is critical for responding to perceived threats
(such as angry or fearful facial expressions) with fear or aggres-
sion. Te cingulate gyrus plays a role in expressing our emo-
tions through gestures and in resolving mental conflicts when
we are frustrated.
Odors oFen trigger emotional reactions and memories.
Tese responses reflect the origin of much of the limbic system
in the primitive “smell brain” (rhinencephalon). Our reactions
to odors are rarely neutral (a skunk smells
bad
and repulses us),
and odors oFen recall memories of emotion-laden events.
Extensive connections between the limbic system and lower
and higher brain regions allow the system to integrate and re-
spond to a variety of environmental stimuli. Most limbic sys-
tem output is relayed through the hypothalamus. Because the
hypothalamus is the neural clearinghouse for both autonomic
(visceral) function and emotional response, it is not surprising
that some people under acute or unrelenting emotional stress
fall prey to visceral illnesses, such as high blood pressure and
heartburn. Such emotion-induced illnesses are called
psycho-
somatic illnesses
.
Because the limbic system interacts with the prefrontal lobes,
there is an intimate relationship between our feelings (mediated
Cognitive Functions of the Cerebellum
Neuroanatomy, imaging studies, and observations of patients
with cerebellar injuries suggest that the cerebellum also plays
a role in thinking, language, and emotion. As in the motor sys-
tem, the cerebellum may compare the actual output of these
systems with the expected output and adjust accordingly. Much
still remains to be discovered about the precise role of the cer-
ebellum in nonmotor functions.
Check Your Understanding
12.
In what ways are the cerebellum and the cerebrum similar?
In what ways are they different?
For answers, see Appendix H.
Functional Brain Systems
Locate the limbic system and the reticular formation, and
explain the role of each functional system.
±unctional brain systems are networks of neurons that work
together but span relatively large distances in the brain, so
they cannot be localized to specific regions. Te
limbic system
and the
reticular formation
are excellent examples.
Table 12.1
summarizes their functions, as well as those of the cerebral
hemispheres, diencephalon, brain stem, and cerebellum.
The Limbic System
Te
limbic system
is a group of structures located on the medial
aspect of each cerebral hemisphere and diencephalon. Its cerebral
structures encircle (
limbus
5
ring) the upper part of the brain stem
(Figure 12.16)
. Te limbic system includes the
amygdaloid body
Corpus callosum
Septum pellucidum
Olfactory bulb
Diencephalic structures
of the limbic system
Anterior thalamic
nuclei (flanking
3rd ventricle)
Hypothalamus
Mammillary body
Fiber tracts connecting
limbic system structures
Fornix
Anterior commissure
Cerebral structures of
the limbic system
Cingulate gyrus
Septal nuclei
Amygdaloid body
Hippocampus
Dentate gyrus
Parahippocampal
gyrus
Figure 12.16
The limbic system.
Lateral view of the brain, showing some of the structures
of the limbic system, the emotional-visceral brain. The brain stem is not illustrated.
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