Download The Cerebellum Anatomically consists of two hemispheres and

The Cerebellum
FARAH NABIL ABBAS
MBCHB-MSC-PHD NEUROPHYSIOLOGY
Anatomically consists of two hemispheres and vermis it
divided by number of fissures into ten lobules and
connected to the brain stem by the peduncles.
The human cerebellar cortex is actually a large folded
sheet, deep beneath the folded mass of cerebellar
cortex lies the deep cerebellar nuclei.
Cerebellum can not initiate muscle function by itself,
instead, it always function in association with other
systems of motor control. Basically the cerebellum
plays major roles in the timing of motor activities
and in rapid, smooth progression from one movement to
the next e.x. running, typing, playing the piano, and
talking.
Cerebellum also helps to control intensity of
muscle contraction when the muscle load changes
and controls the necessary interplay between
agonist & antagonist muscle groups.
The cerebellum is recognized as the “silent area
of the brain”, because electrical excitation
doesn’t cause any sensation and rarely causes
any motor movement.
Removal of cerebellum, however, does cause
movement to be highly abnormal with marked incoordination; however No Paralysis of any muscle
could be found.
Anatomical Functional Areas of Cerebellum
The Anterior Lobe.
The Posterior Lobe.
The Flocculonodular Lobe along with vestibular
system responsible for equilibrium.
The center of the cerebellum has a narrow band
called the Vermis, it is the area for control of
axial body, neck, shoulders and hips muscle
movements. Next to vermis, The Intermediate Zone,
the site for the distal muscle control especially
hands and feet, even more lateral, The Lateral
Zone, is situated and is responsible for tiring of
coordination of muscle movements with the help of
cerebral cortex, its damage leads to
in-coordination.
Input Pathways to Cerebellum
A.Afferent from other parts of brain:
1.From cerebral cortex through the corticosponto cerebellar pathway,
the largest source of Mossy fibers which transmit information about
muscle movements planned by cortex.
2.From olivary nucleus through olivocerebellar tract.
From vestibular apparatus or from brainstem vestibular nuclei through
vestibulocerebellar pathway.
3.From reticular formation through the reticulocerebellar pathway.
B.Afferents from the periphery:
1.Dorsal spinocerebellar tract, comes mainly from muscle spindle, and
apprises the cerebellum about body parts movements, dynamic and
static muscle length and tension.
2.Ventral spinocerebellar tract, excited mainly by the motor signals
arriving in the anterior horns of spinal cord from brain through
corticospinal and rubrospinal tracts and from spinal cord. This pathway
informs cerebellum which motor signals have arrived at anterior horns.
 The Input Arranged into:
 1. Climbing Fibers: all originate from inferior
olive of medulla, characterized by single
prolonged peculiar action potential (complex
spike) in each Purkinje cell, these fibers are
synapse too. They are the excitatory fibers.
 2. Mossy Fibers: characterized by much weaker
short duration action potential (simple spike) on
Purkinje cell. Many Mossy fibers must be
stimulated simultaneously to excite the Purkinje
cell. The Mossy fibers are all the other fibers that
enter the cerebellum from higher brain,
brainstem and spinal cord other fibers that enter
the cerebellum from higher brain, brainstem and
spinal cord.
 Output Pathways from Cerebellum
 1. From vermis to medullary and pontine regions
of brainstem this circuit controls equilibrium
along with vestibular nuclei.
 2. From Intermediate zone to ventrolateral and
ventroanterior nuclei of thalamus, to cerebral
cortex, basal ganglia, red nucleus and reticular
formation. This complex circuit helps to
coordinate reciprocal contractions of agonist and
antagonist muscles in limbs especially hands,
fingers and thumbs.
 3. From lateral zone to dentate nucleus and then
to the cerebral cortex. This pathway helps to
coordinate sequential motor activities initiated
by cerebral cortex.
 Functional Unit of Cerebellar Cortex
 Cerebellar Cortex: it has five neurons: Purkinje, Granule,
Basket, Stellate, and Golgi cells.
 The axons of Purkinje cells are inhibitory and are the only output
from cerebellar cortex to deep nuclei.
 The Granule cells (excitatory) receive input from the Mossy
fibers and send the bifurcated axons (parallel fibers) to synapse
with other cerebellar cortical cells.
The Stellate and Basket cells are inhibitory inter-neurons, which
synapse with Purkinje cells.
 Golgi cells are inhibitory inter-neurons which receive input from
parallel fibers, Mossy fibers and Purkinje cells and send
inhibitory signals to granule cells.
 Deep Cerebellar Nuclei:
They are Dentate, Globose, Emboliform and Fastigle nuclei. 
 Receive excitatory inputs from Mossy and climbing fibers and
inhibitory inputs from Purkinje cells.
 The outputs of deep cerebellar nuclei to brainstem and
thalamus and its always excitatory.
The Cerebellar Neuronal Circuit Major Features 
 Input-output signals are very rapid and no
reverberating.
 All cerebellar cortical cells are inhibitory except
Granule cells are excitatory.
 All cerebellar cells are constantly active.
Climbing fibers inputs exert a strong excitatory 
effect on single Purkinje cells whereas Mossy
fibers inputs exert a weak excitatory effect on
many Purkinje cells via the Granule cells in
addition to excitation of other cells (Basket and
Stellate cells) which are inhibitory to Purkinje
cells and Gogli cells which inhibit the
transmission from Mossy fibers to Granule cells.
The Main Functions of Cerebellum
 1.Damping function of the cerebellum i.e.
preventing
“overshoot”
by
monitoring,
comparing and making corrective adjustments
between the signals of higher motor centers and
the actual motor response at the level of anterior
motor neurons.
 In cerebellar dysfunction overshooting does
occur (Dysmetria or Past Pointing) trying to
make corrections to this overshoot, the arm
oscillate back and forth several times before it
finally fixes on its target (Intention Tremor).
 2.Planning, programming and timing the next
movement at the same time of present
movement with help of motor cortex, sensory
cortex and basal ganglia.
 In
cerebellar dysfunction extreme incoordination and failure of progression of the
purposeful movements of hands, fingers and
feet which is called Dysdiadochokinesia.
 Speech is also affected (Dysarthria) due to lack
of coordination between individual muscles of
larynx, mouth and respiratory system, leading to
load syllables and others weak, some long,
others short.
 3.Control of equilibrium: because cerebellum is
responsible for controlling the balance between
agonist and antagonist muscles during changes
if body position. Cerebellar dysfunction leads to
Cerebellar ataxia.
 4.Control of ballistic movements e.x. movement
of fingers in typing or eye movements when
reading, the control of these movements are
cerebellar functions.
5.Role of cerebellum in predicting the rate of
progression of auditory and visual stimuli e.x. a
person can predict from the change in visual
scenes how rapidly he is approaching an object.
Clinical Abnormalities of Cerebellum
Dysmetria: an attempt to touch an object with a
finger results in overshooting to one side or
other.
Intention tremor: finger oscillation back and
forth - absent at rest and appears whenever
patient attempt to perform some voluntary
action.
Rebound phenomenon: patient inability to "put
on brakes", to stop movement promptly (flexion
against resistance and sudden release).
Clinical Abnormalities of Cerebellum
Dysdiadochokinesia: Inability to perform rapidly
alternating opposite movements (repeated hand
supination and pronation).
Hypotonia: muscle tone  on side of cerebellar
lesion especially when dendate and interposed
nuclei were damaged.
Nystagmus: Damage of flocculonodular lobe
damage  rapid eye movements when attempts
to fixate eyes on a view to one side of head.