Cerebellum Flashcards
Cerebellum unconsciously influences the
smooth contraction of voluntary
muscles and carefully coordinates their actions, together with the
relaxation of their antagonists
Each cerebellar hemisphere controls
muscular movements on the
same side of the body and the cerebellum has no direct
pathway to the lower motor neurons but exerts its control via the
cerebral cortex and the brainstem
control of posture and voluntary movements
Cerebellum
Cerebellum location
Posterior Cranial Fossa
Largest part of the Hindbrain
Cerebellum
Cerebellum lies posterior to the
fourth ventricle, the pons,
and the medulla oblongata
Three main lobes of the cerebellum
the anterior lobe,
the middle lobe, and the flocculonodular lobe
seen on the superior surface of the
cerebellum
Anterior lobe
Anterior lobe is separated to the middle lobe by a wide V-shaped fissure
primary fissure
Associated lobule to the ant. lobe
Quadrangular Ala of Central lobule
largest part of the cerebellum
Middle lobe
middle lobe is situated between the
primary and uvulonodular fissures
Associated lobule of the middle lobe
Simplex
Superior semilunar
Inferior semilunar
Biventral
Tonsil
lies posterior and inferior to, separated bu
anterior lobe, primary fissure tonsil
Cerebellar tonsils lie just lateral to the
medulla and, if displaced by pressure, can compress the medulla,
causingg death
tonsillar herniation
flocculonodular lobe is situated posterior to the
uvulonodular
fissure
Associated lobule of the flocculonodular lobe
Flocculus nodule of the vermis
Flocculus is separated from the middle lobe
by
posterolateral fissure
Significance of the flocculonodular lobe
involved in balance by communicating
with vestibular system
atrophic in alcoholics
Anterior lobe
composed of an outer covering of gray matter called the __
and__
cortex, inner white matter
Embedded in the white matter of each hemisphere are three
masses of gray matter forming the
intracerebellar nuclei
Each fold or folium contains a core of white matter covered
superficially by gray matter
Cerebellar Cortex
3 layers of gray matter
an external layer, the molecular layer
a middle layer, the Purkinje cell layer
an internal layer, the granular layer
molecular layer contains two types of neurons
outer stellate cell and the inner basket cell
These neurons are scattered among __
and numerous thin axons that run parallel to the long axis of
the folia. __ are found between these structures
dendritic arborizations, Neuroglial cells
flask shaped and are arranged in a single layer.
Purkinje cells are large Golgi type I
At the base of the Purkinje cell, the axon arises and
passes through the ___ to enter the white
matter
granular layer
Collateral branches of the Purkinje axon make synaptic
contacts with the dendrites of __of the granular layer in the same area or in
distant folia.
basket and stellate
cells
Granular layer is packed with small cells with densely staining nuclei
and scanty cytoplasm. Each cell gives rise to __
dendrites, which make claw-like endings and have
synaptic contact with __
4/5, mossy fiber input
Granular layer
The axon of each granule cell passes into the __
layer, where it bifurcates at a __junction , the
branches running parallel to the long axis of the
__
molecular layer, T , cerebellar folium
run at right angles
to the dendritic processes of the Purkinje cells.
parallel fibers
influences the movements of the long axis of the
body , namely, the neck, the shoulders, the thorax, the
abdomen, and the hips
Vermis
to control the muscles of the distal parts of the
limbs, especially the hands and feet.
intermediate
zone of the cerebellar hemisphere
Immediately lateral to the vermis is a so-called
intermediate
zone of the cerebellar hemisphere
concerned with the planning of sequential movements of
the entire body and is involved with the conscious
assessment of movement errors.
lateral zone of each cerebellar hemisphere
Intracerebellar Nuclei
- Dentate, Globus & Emboliform, Fastigial
: largest, lateral-most deep nucleus
Dentate Nucleus
Dentate Nucleus Input & Output
Input: Lateral Hemisphere
Output: SCP
Globose Nuclei & Emboliform nucleus collectively
Interposed nucleus
Interposed Nucleus Input & Output
Input: Paravermin
Output: SCP
medial-most deep nucleus
Fastigial Nucleus
Fastigial Nucleus
Input & Output
Input: Vermis
Output: juxtarestiform body
of the inferior cerebellar peduncles
closely resembles the trunk and branches of a tree and thus is
termed
arbor vitae
amount of white matter in each cerebellar hemisphere. The
white matter is made up of three groups of fibers:
intrinsic, afferent, efferent
do not leave the cerebellum but connect
different regions of the organ. Some interconnect folia of the
cerebellar cortex and vermis on the same side; others connect
the two cerebellar hemispheres together
Intrinsic fibers
form the greater part of the white matter
and proceed to the cerebellar cortex. They enter the cerebellum
mainly through the inferior and middle cerebellar peduncles
Afferent fibers
constitute the output of the cerebellum and
commence as the axons of the Purkinje cells of the cerebellar
cortex
The efferent fibers
two main lines
of input to the cortex and are excitatory to the Purkinje cells
climbing and the mossy fibers
terminal fibers of the olivocerebellar tracts
climbing fibers
terminal fibers of all other cerebellar
afferent tracts.
mossy fibers
The deep cerebellar nuclei receive afferent nervous
information from two sources:
the inhibitory axons from the Purkinje cells of the
overlying cortex
the excitatory axons that are branches of the afferent
climbing and mossy fibers that are passing to the
overlying cortex.
the excitatory climbing and mossy afferent fibers use
Gamma-aminobutyric acid (GABA)
other afferent fibers entering the cortex liberate
norepinephrine and serotonin
superior cerebellar peduncles connect the cerebellum to
midbrain
middle cerebellar peduncles connect the cerebellum to
the
pons
the inferior cerebellar peduncles connect the cerebellum
to the
medulla oblongata
arise from nerve cells in the
frontal, parietal, temporal, and occipital lobes of the
cerebral cortex and descend through the corona radiata
and internal capsule and terminate on the pontine nuclei
corticopontine fiber
The pontine nuclei give rise to the
transverse fibers of the
pons
cross the midline and enter the opposite
cerebellar hemisphere as the middle cerebellar peduncle
arise from nerve cells in the frontal, parietal, temporal, and
occipital lobes of the cerebral cortex and descend
through the corona radiata and internal capsule to
terminate bilaterally on the inferior olivary nuclei
Cerebro-olivocerebellar pathway
Cerebro-olivocerebellar pathway
give rise to fibers that cross the midline and enter the
opposite
cerebellar hemisphere through the inferior
cerebellar peduncle.
These fibers terminate as the
climbing fibers in the cerebellar cortex
arise from nerve cells from many areas of the cerebral
cortex, particularly the sensorimotor areas.
Cerebroreticulocerebellar Pathway
They descend to terminate in the reticular formation on
the same side and on the opposite side in the pons and
medulla
Cerebroreticulocerebellar Pathway
This connection between the cerebrum and the
cerebellum is important in the control of voluntary
movement
Cerebroreticulocerebellar Pathway
anterior spinocerebellar tract
enter: PRG> Nucleus dorsalis of Clarke @ base of PGH
Cross opp side in contralat white column
Enter cerebellum via SCP
Terminate as mossy fibers
upper and
lower limbs.
posterior spinocerebellar tract
Posterolat of lat white column
ascend to medulla oblongata
Enter in ICP
Terminate as mossy fibers
trunk and lower
limbs
cuneocerebellar tract
terminate as mossy fibers in the cerebellar
cortex.
Collateral branches that end in the deep cerebellar
nuclei are also given off
upper limb and upper part of
the thorax
The vestibular nerve sends many afferent fibers directly to
the cerebellum through the
inferior cerebellar peduncle on
the same side
receives information from the inner ear concerning motion
from the semicircular canals and position relative to gravity
from the utricle and saccule
Cerebellar Afferent Fibers From the
Vestibular Nerve
vestibular afferent fibers pass
first to the vestibular
nuclei in the brainstem, where they synapse and are relayed
to the cerebellum
All the afferent fibers from the inner ear terminate as mossy
fibers in the flocculonodular lobe of the cerebellum.
Axons of neurons in the globose and emboliform nuclei
travel through the
superior cerebellar peduncle
the globose and emboliform nuclei influence
motor
activity on the same side of the body.
Axons of neurons in the dentate nucleus travel through
the superior cerebellar peduncle and cross the midline to
the opposite side in the decussation of the
superior
cerebellar peduncle.
dentate nucleus can influence
motor activity by acting on the motor neurons of
the opposite cerebral cortex; impulses from the motor
cortex are transmitted to spinal segmental levels
through the corticospinal trac
the dentate nucleus is able to
coordinate muscle
activity on the same side of the body
The axons of neurons in the fastigial nucleus travel
through the
inferior cerebellar peduncle and end by
projecting on the neurons of the lateral vestibular
nucleus on both sides
The fastigial nucleus exerts a facilitatory influence
mainly on the
ipsilateral extensor muscle tone
The axons of neurons in the fastigial nucleus travel
through the
inferior cerebellar peduncle
Fastigial Reticular Pathway influence
spinal segmental
motor activity through the reticulospinal tract
produce sudden, severe symptoms and signs,
patients can recover completely from large cerebellar injuries.
other CNS areas can compensate for loss of cerebellar function
Acute lesions
such as slowly enlarging tumors, produce
symptoms and signs that are much less severe than those of
acute lesions. The reason for this may be that other CNS areas
have time to compensate for loss of cerebellar function
Chronic lesions,
- muscles lose resilience to palpation. There is
diminished resistance to passive movements of joints. Shaking the
limb produces excessive movements at the terminal joints. The
condition is attributable to loss of cerebellar influence on the
simple stretch reflex
Hypotonia
Postural Changes and Alteration of Gait
head is often rotated and flexed, and the shoulder on the side
of the lesion is lower than on the normal side.
The patient assumes a wide base when he or she stands and is
often stiff legged to compensate for loss of muscle tone. When the
individual walks, he or she lurches and staggers toward the
affected side
Tremor occurs
when fine movements, such as buttoning clothes, writing, and
shaving, are attempted. Muscle groups fail to work harmoniously,
and there is decomposition of movement
Ataxia/Disturbances in Voluntary movement
is the inability to perform alternating
movements regularly and rapidly
Dysdiadochokinesia
essentially an ataxia of the ocular muscles, is a
rhythmical oscillation of the eyes
Nystagmus,
cerebellar disease because of ataxia of the
muscles of the larynx
Dysarthria
The most common cause of vermis
syndrome is a__ of the vermis in children.
Involvement of the flocculonodular lobe results in signs and
symptoms related to the vestibular system. There is a tendency to
fall forward or backward. There is difficulty in holding the head
steady and in an upright position
Vermis Syndrome, medulloblastoma
This rhythmic oscillation of the eyes may be of the same rate in
both directions
pendular nystagmus
