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No. 24
1. Cerebellum
2. Diencephalon
Ⅱ. The Cerebellum
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The cerebellum is the second of large
portion of the brain lying behind the pons
and medulla oblongata, and its median
portion is separated from them by the
cavity of fourth ventricle. It is located in
the posterior cranial fossa and is covered
by the tentorium of cerebellum.
Ⅰ) External Features and divisions
1. External features of the cerebellum and
its morphological lobes
 The cerebellum is composed of two lateral
cerebellar hemispheres connected in
the midline by a structure called the
vermis.
 The surface of the cerebellum consists of a
thin cortex of gray matter. The cortex dips
deeply below the apparent surface of the
cerebellum in a manner similar to the
fissures and sulci of the cerebrum.
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The surface of cerebellum is composed of
numerous narrow transverse folds, laminae or
cerebellar folia.
Some deeper fissures divide the organ into lobes
or lobules.
The horizontal fissure extends around the lateral
and posterior borders of each hemisphere and
marks the junction of the superior and inferior
surfaces of the cerebellum.
The tonsils of cerebellum are two elevated
masses on the inferior surface of the hemispheral
portion just behind the flocculonodular and
nearby the foramen magnum.
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The cerebellum presents three regions according
to the external features.
① Flocculonodular
It consists of both flocculi, their peduncles and
the nodule.
② Anterior lobe
It is that part of the superior surface rostral to
the primary fissure.
③ Posterior lobe
The remainder of the cerebellum on both surfaces
constitutes the posterior lobe.
Anterior and posterior lobes constitute the corpus
of cerebellum.
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2. Functional region of cerebellum
The cerebellum can be divided by its connections
and phylogeny into three portions.
① Vestibulocerebellum or archicerebellum
The flocculonodular lobe is predominantly
vestibular in its connections and constitutes the
oldest part of the cerebellum.
② Spinocerebellum or paleocerebellum
The anterior lobe and the rostral part of the
inferior vermis are predominantly spinocerebellar
in its connections.
③ Cerebrocerebellum or neocerebellum
The posterior lobe is predominantly
corticopontocerebellar in its connections.
Ⅱ) Internal Structure
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1. The cerebellar cortex
Structurally, the cerebellum consists of a
cerebellar cortex or surface layer of gray
matter, a medullary center of white matter,
and four pairs of central nuclei embedded
in the medullary center.
From the surface to the white matter of
the folium, these are the molecular layer,
the Purkinje cell layer, and the
granular layer.
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2. The central nuclei of the cerebellum
Four pairs of nuclei are embedded deep in the
medullary center, they are the fastigial, globose,
emboliform, and dentate nuclei.
The dentate nucleus is the largest one and lies
most laterally. It receives the fibers from the
cerebellar cortex. The efferent fibers arise from
the dentate nucleus forming the major part of the
superior cerebellar peduncle to reach the red
nucleus and the thalamus of contralateral side.
Ⅲ) The fibrous connections and
functions of cerebellum
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1. The fibrous connections and functions
of vestibulocerebellum or archicerebellum
(1) Fibrous connections
① Afferent fibers
The vestibulocerebellar fibers from the
vestibular nuclei and vestibular nerve to
the vestibulocerebellum from the inferior
cerebellar peduncles.
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② Efferent fibers
The fibers proceed from the vestibulocerebellum
(flocculonodular lobe), relay in the fastigial
nucleus and get to the vestibular nuclei and the
reticular formation in the medulla oblongata and
pons, then through the vestibulospinal tract and
medial longitudinal fasciculus, control the
muscles of trunk and extraocular muscles.
(2) Function
The vestibulocerebellum is concerned with the
maintenance of equilibrium and body posture.
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2. The fibrous connections and functions of
spinocerebellum or paleocerebellum
(1) Fibrous connections
① The afferent fibers
The fibers of anterior and posterior
spinocerebellar tract go through the superior and
inferior cerebellar peduncles respectively and get
to the spinocerebellum.
② The efferent fibers
The efferent fibers from the cortex of
spinocerebellum, relay in the globose and
emboliform, get to the red nucleus of opposite
side.
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(2) Function
The spinocerebellum influences muscle
tone and synergy of muscles during
stereotyped movements such as those of
postural changes and locomotion.
3. The fibrous connections and function of
cerebrocerebellum or neocerebellum
(1) Fibrous connections
① The afferent fibers
 The afferent fibers from the contralateral
pontine nucleus and inferior olivary
complex form the pontocerebellar tract
and olivocerebellar tract respectively. They
get to the cerebrocerebellum through the
middle and inferior cerebellar peduncles.
② The efferent fibers
 The efferent fibers arising from the
cerebrocerebellum, relay in the dentate
nucleus, and get to the contralateral red
nucleus, ventral intermediate nucleus and
ventral anterior nucleus of dorsal
thalamus.
(2) Function
 The cerebrocerebellum ensures the
coordination of muscles for accuracy of
nonstereotyped movements.
Ⅳ) Clinical expression after
cerebellar damnification
1. Archicerebellar syndrome.
(1) Imbalance of equilibrium
 The archicerebellar syndrome is
characterized by the disturbance of
equilibrium. The patient is unsteady when
standing, walks on a wide base, the gait
resembles that of a drunken individual
(cerebellar gait) and sways from side to
side even falls backward or to either side.
(2) Quiver of eyeball
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2. Paleocerebellar syndrome
It is characterized by the disturbance of
postural reflex, in which the subject
staggers or cannot coordinate normal
walking movement.
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3. Neocerebellar syndrome
It has the following characteristic signs:
(1) Ataxia: It is due to incoordination of the
related muscles. For instance, the patient cannot
touch the tip of his nose with a finger without
looking at this finger, because he cannot
coordinate movement with his sense of where a
body part is located.
Adiadochokinesia, rapidly successive movements,
such as alternately pronating and supinating the
forearms are poorly performed.
(2) Reducing of muscle tone.
(3) Intention tremor.
Ⅲ. The Diencephalon
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The diencephalon, being almost entirely
surrounded by the hemispheres of the cerebrum,
exposes only the ventral surface of the
diencephalon to view in a diamond-shaped area
containing hypothalamic structures.
The diencephalon is divided into symmetrical
halves by the slitlike third ventricle.
The medial surface of the diencephalon forms the
wall of the third ventricle.
Thalamic medullary stria (stria terminalis).
The diencephalon consist of five components or
regions on each side, named the:
dorsal thalamus, epithalamus, subthalamus,
metathalamus, and hypothalamus.
Ⅰ) The Thalamus (dorsal thalamus)
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Each of the two thalami is a large ovoid
mass of gray matter, making up four-fifths
of the diencephalon.
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1.The nuclei of dorsal thalamus
The internal medullary lamina,
consisting mainly of a band of
myelinated fibers, divides the thalamus
into three nuclear groups.
the anterior nuclear group,
the medial nuclear group,
the lateral nuclear group.
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(1) The anterior nuclear group is enclosed by
a bifurcation of the lamina and forms a
rostromedial swelling known as the anterior
tubercle.
(2) The medial nuclear group contains the
large dorsomedial nucleus.
(3) The lateral nuclear group consists of
ventral and dorsal tiers of nuclei which have been
identified because of differing fiber connections.
Three nuclei are recognized in the ventral tier:
Ventral anterior nucleus,
Ventral lateral nucleus,
Ventral posterior nucleus.
The ventral posterior nucleus consists of ventral
posteromedial nucleus and ventral
posterolateral nucleus.
2. The nucleus classified on the basis of phylogeny
 On the basis of phylogeny, connections with other
parts of the brain, and function, the thalamic
nuclei may be classified according to the
following scheme.
(1) Nonspecific projection nuclei (archithalamus)
 They are composed of midline nuclei,
intralaminar nuclei, and reticular nucleus.
 The midline nuclei lie in the periventricular gray
matter of the thalamus and in the interthalamic
adhesion.
In the central part of the thalamus, the
internal medullary lamina partially
encloses the intralaminar nuclei, including
the well-developed centromedian
nucleus.
 Nonspecific projection nuclei receive the
afferent fibers from the olfactory brain and
reticular formation of brain stem. The
ascending fibers of reticular formation
pass through these nuclei and project
extensive area of cerebral cortex, forming
ascending reticular activating system,
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(2) Specific projection (relay) nuclei
(paleothalamus)
They include the ventral anterior, lateral,
and posterior nuclei, and send the fibers
to sensory and motor areas of cortex.
The ventral posteromedial nucleus
receives the fibers from the
trigeminothalamic tract.
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The ventral posterolateral nucleus receives
the fibers from the medial lemniscus and
spinothalamic tract.
The nerve fibers leave the ventral
posteromedial and posterolateral nuclei
form the thalamocortical tract, traverse
the internal capsule and medullary center
of the cerebral hemisphere, and end in the
general sensory area of cortex in the
parietal lobe
(3) Association nuclei (neothalamus)
 They include anterior nucleus, medial
nucleus, and dorsal tier of lateral nucleus.
 The dorsal tier consists of the pulvinar,
lateral posterior nucleus and lateral dorsal
nucleus.
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3.Functions of thalamus
The thalamus is a relay station under the
cortex.
The thalamus is a complex center for
regulation of somatic motion, emotion,
memory, and so on.
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Thalamic syndrome:
The thalamic syndrome is essentially a
disturbance of these aspects of thalamic
functions, subsequent to a lesion involving the
thalamus or its connections. The symptoms vary
according to the location and extent of the lesion.
The threshold for touch, pain and temperature is
usually raised on the opposite side of the body,
but when the threshold is reached the sensations
are exaggerated, perverted and exceptionally
disagreeable. For example, the prick of a pin may
be felt as a severe burning sensation, and even
music that is ordinarily pleasing may be
disagreeable. There is spontaneous pain in some
instances, which may become intractable to
analgesics.
Ⅱ) The metathalamus
 It includes medial geniculate body and
lateral geniculate body.
 The medial geniculate body is the relay
station of acoustic pathway, and gives rise
to the acoustic radiation.
 The lateral geniculate body is the relay
station of visual pathway, and gives rise to
the optic radiation.
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Ⅲ) The epithalamus
It occupies the caudal roof of the third
ventricle together with adjacent areas.
It includes the right and left habenular
nuclei, each situated deep to the floor of
a habenular trigone.
The epithalamus also includes the
habenular commissures.
The pineal body, an endocrine gland in
mammals, is attached to the posterior
commissure on the midline.
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Ⅳ) The subthalamus
The subthalamus is situated immediately ventral
to the dorsal thalamus, in part lateral to the
hypothalamus, and emerges caudally with the
tegmentum of midbrain. The region includes the
rostral extension of the red nucleus and
substantia nigra, the prominent subthalamic
nucleus. Caudally the medial part of the nucleus
overlies rostral portions of the substantia nigra.
It is a component of the extrapyramidal system.
Ⅴ) The Hypothalamus
 As the name indicates, the hypothalamus lies
below the thalamus, where it forms part of the
walls and floor of the third ventricle. Like the
thalamus, the hypothalamus is composed of
several nuclei, each of which is involved with
specific functions.
1. Morphology
 Hypothalamic structures include:
 mammillary bodies,
 tuber cinereum,
 infundibulum,
 optic chiasma,
 hypophysis..
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The mammillary bodies are distinct
swellings on the ventral surface.
Located just anterior to the mammillary
bodies is the tuber cinereum.
Extending downward from the tuber
cinereum is the stalklike infundibulum.
Anterior to the infundibulum is the optic
chiasma, which is formed by the
decussation (crossing) of some of the
neurons in the optic nerves.
Inferior to the infundibulum is the
hypophysis.
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2. Division and main nuclei
The hypothalamus consists of four areas.
Anteroptic area:
Supraoptic area: Includes paraventricular
nucleus and supraoptic nucleus.
Tubar area: Includes infundibular nucleus.
Mammillary area. Includes mammillary
nucleus.
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3. Fibrous connections of hypothalamus
(1) The connection with the limic system
(2) The connection with the brain stem and spinal
cord
(3) The connection with the dorsal thalamus
(4) The connection with the hypophysis
Hormones produced by neurons in the
hypothalamus have been sent to the posterior
lobe (neurohypophysis) through
paraventriculohypophyseal tract and
supraopticohypophyseal tract.
4. Functions of hypothalamus
(1) Hypothalamus is a center of endocrine
system. The hypothalamus also regulates the
release of the hormones of the pituitary gland
and thus, to a large extent, it controls the
endocrine system.
(2) The hypothalamus controls many vital
processes, most of them associated with the
autonomic nervous system. Some of the
hyopothalamic nuclei have been shown
experimentally to regulate sympathetic activity;
others control parasysmpathetic functions.
(3) The hypothalamus is involved in regulating
body temperature, water balance, appetite,
gastrointestinal activity, sexual activity, and even
emotions such as fear and rage.
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The third ventricle
The third ventricle is a narrow cavity in
the diencephalon. It is between the two
dorsal thalami and hypothalamus.
Cerebrospinal fluid enters the third
ventricle from each lateral ventricle
through the interventricular foramen.
The fluid leaves the third ventricle by way
of the mesencephalic aqueduct,
through which it reaches the fourth
ventricle.