410
UNIT THREE
the cerebellum via the spinal cord and medulla oblongata.
The
middle peduncles
transmit information from the cerebral
cortex about the desired position of these body parts. After
integrating and analyzing the information from these two
sources, the cerebellum sends correcting impulses from the
dentate nucleus via the
superior peduncles
to the midbrain
(F g. 11.22). These corrections are incorporated into motor
impulses that travel downward through the pons, medulla
oblongata, and spinal cord in the appropriate patterns to
move the body in the desired way.
Overall, the cerebellum integrates sensory informa-
tion concerning the position of body parts and coordinates
skeletal muscle activity and maintains posture. It receives
sensory impulses from receptors in muscles, tendons, and
joints (proprioceptors) and from special sense organs, such
as the eyes and ears. ±or example, the cerebellum uses sen-
sory information from the semicircular canals of the inner
ears concerning the motion and position of the head to help
maintain equilibrium (see chapter 12, pp. 459–461). Damage
to the cerebellum can cause tremors, inaccurate movements
of voluntary muscles, loss of muscle tone, a reeling walk,
and loss of equilibrium.
Table 11.7
summarizes the characteristics and functions
of the major parts of the brain. Clinical Application 11.6 dis-
cusses how brain waves refl
ect brain activity.
PRACTICE
30
Where is the cerebellum located?
31
What are the major functions of the cerebellum?
32
What types of receptors provide information to the cerebellum?
PRACTICE
25
What are the major functions of the thalamus? Of the
hypothalamus?
26
How may the limbic system inF
uence a person’s behavior?
27
Which vital reF
ex centers are located in the brainstem?
28
What is the function of the reticular formation?
29
Describe two types of sleep.
Cerebellum
The
cerebellum
(ser
e
˘-bel
um) is a large mass of tissue located
inferior to the occipital lobes of the cerebrum and posterior to
the pons and medulla oblongata (see F g. 11.15). It consists of
two lateral hemispheres partially separated by a layer of dura
mater called the
falx cerebelli.
A structure called the
vermis
connects the cerebellar hemispheres at the midline.
Like the cerebrum, the cerebellum is primarily composed
of white matter with a thin layer of gray matter, the
cer-
ebellar cortex,
on its surface. This cortex doubles over on
itself in a series of complex folds that have myelinated nerve
F bers branching into them. A cut into the cerebellum reveals
a treelike pattern of white matter, called the
arbor vitae,
sur-
rounded by gray matter. A number of nuclei lie deep within
each cerebellar hemisphere. The largest and most important
is the
dentate nucleus.
The cerebellum communicates with other parts of the
CNS by means of three pairs of nerve tracts called
cerebellar
peduncles
(ser
e
˘-bel
ar pe-dung
kls)
(f
g. 11.22)
. One pair,
the
inferior peduncles,
brings sensory information concern-
ing the position of body parts such as limbs and joints to
Thalamus
Superior peduncle
Middle peduncle
Inferior peduncle
Pons
Medulla oblongata
Cerebellum
Corpus callosum
Longitudinal
fissure
FIGURE 11.22
The cerebellum, located inferior to the occipital lobes of the cerebrum, communicates with other parts of the nervous system by
means of the cerebellar peduncles.
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