Download Lateral Zone

AZRA NAHEED MEDICAL
COLLEGE
DEPARTMENT OF PHYSIOLOGY
DR.TAYYABA AZHAR
• The Largest part of Hind Brain and it is
posterior to pons and medulla oblongata,
located in posterior cranial fossa, covered by a
layer of dura matter i.e. tentorium cerebelli.
• Cerebellum consists of 2 cerebellar hemispheres with narrow middle
vermis.
• Can be divided into 3 lobes i.e. anterior, middle or posterior lobe,
floculonodular lobe.
• Developmentally cerebellum is divided into three parts i.e. paleo, neo
and archi cerebellum.
• Paleo cerebellum is the old part and consists of anterior lobe and uvula
and pyramid of vermis.
• Neo cerebellum is middle or posterior cerebellum minus uvula and
vermis.
• Archi cerebellum is the oldest part and consists of floculo nodular lobe.
• On the surface of cerebellum there is grey matter known as cortex and
core is white matter.
• Cortex is thrown in folds known as folea which has fissures and gyri.
• In cut section there is branched appearance. This appearance is called
Arbor Vitae.
• Each cerebellar hemisphere is divided into two parts i.e.
intermediate zone and lateral zone.
• In the vermis and in the intermediate zone, there is
topographical representation of different parts of body.
• In the vermis axial parts of body are represented while in
the intermediate zone limbs and facial parts are
represented.
• In lateral zone there is no topographical representation.
This representation receives afferent fibers from the
respective parts of motor cortex. Similarly it receives
afferent fibers from the respective parts of body and also
from motor nuclei of brain stem.
• Efferents go to respective parts in motor cortex, red
nucleus and reticular formation.
Cerebellum
Intermediate part
Lateral part
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LOBULES
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There are 10 primary lobules in the vermis.
1st lingula
2nd and 3rd central lobule
4th culmen
5th declive
6th folium
7th tuber
8th pyramid
9th uvula
10th nodule
STRUCTURE OF CEREBELLAR CORTEX
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it is composed of three layers of grey matter.
Molecular layer:
outer most.
It consists of outer stellate and inner basket cells.
it contains dendrites and nerve fibers which come from the deeper layers.
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Purkinge cell layer:
It consists of single layer of purkinge cells. These are flask shaped.
From the top of these cells dendrites arise and pass into the molecular layer,
where these give rise to primary secondary and tertiary branches.
From the base of these cells axons arise which pass to the deeper layers and then
these axons enter the white matter and become myelinated. Most of the axons
from purkinge cells synapse with the neurons in the deep cerebellar nuclei or intra
cerebellar nuclei.
Some of the axons bypass the deep cerebllar nuclei to go to the vestibular nuclei
and these axons which bypass are perhaps from vermis or floculonodular lobe.
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• Granular layer
• it is composed of granule cells.
• There axons pass into the molecular layer where
these end into T shaped terminals or endings
which synapse with the dendrites of purkinje
cells.
• Golgi cells are also present in the granular layer.
Dendrites of golgi cells pass to the molecular
layer while their axons synapse with the
dendrites of the granule cells.
• White matter of cerebellum consists of three types of nerve fibers i.e.
• Intrinsic fibers:
• These are the nerve fibers which pass from the cerebellar cortex to vermis
and also from one cerebellar hemisphere to the other. So these remain
within the cerebellum.
• Climbing Fibers:
• These come from the inferior olivary nuclei. These fibers give collaterals
to synapse with neurons in the deep cerebellar nuclei. Then these fibers
go to the molecular layer to synapse with the dendrites of purkinge cells
• Mossi Fibers:
• These are all the other afferent nerve fibers other than climbing fibers.
These also give collateral to synapse with neurons in the deep cerebellar
nuclei and then these pass into the granular layer where these synapse
with dendrites of granule cells.
• Afferent nerve fibers mainly enter the
cerebellum through anterior and middle
cerebellar peduncles.
• Efferent fibers from the cerebellum begin as
the axons of purkinge cells. Most of these
synapse with deep cerebellar nuclei.
• Then axons from the deep cerebellar nuclei
arise and these form the efferents from the
cerebellum.
NUCLEI
• DEEP CEREBELLAR NUCLEI: There are four nuclei on
each side. From lateral to medial side these are
• Dentate
• Emboliform
• Globos
• Festigial
• Emboliform and Globos are collectively called as
nucleus interpositus.
• Efferent fibers from 1st three come out of the
cerebellum from superior cerebellar peduncle.
• Efferent from the last one come out through the
inferior cerebellar peduncle.
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CONNECTIONS OF CEREBELLUM
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Cerebellum is connected to brain stem through three peduncles i.e.
Superior to the midbrain
Middle to the pons
Inferior to the medulla oblongata
These peduncles contain both afferent and efferent fibers.
INFERIOR CEREBELLAR PEDUNCLE:
– Afferents: these include
• posterior spino cerebellar tract
• cuneo cerebellar tract which are also called as posterior external arcuate fibers
• vestibule cerebellar tracts which are from the vestibular nuclei
• olivocerebeallar from olivary nuclei
• reticulo cerebellar fibers which arise from reticular formation
– Efferents:
• Cerebello vestibular
• Cerebello reticular
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MIDDLE CEREBELLAR PEDUNCLE: Largest of the three peduncles.
– Pontocerebellar fibers: main fibers and form part of corticoponto and
cerebellar pathway.
SUPERIOR CEREBELLAR PEDUNCLE:
– Afferent:
• Anterior spino cerebellar tract
• Rubro cerebellar tract from red nucleus
• Tacto cerebellar tract from tactum of mid brain
– Efferents: these go to the
• Ventroanterior and ventrolateral nuclei of thalamus and then these go to
the cerebral cortex.
• Some go to the red nucleus from where they go to the thalamic nuclei
and then to cerebral cortex.
• Some also go to the basal ganglia.
So cerebellum has got the reciprocal connections with the cerebral cortex, red
nucleus, vestibular nuclei, reticular formation. So these connections indicate the
basis of functions of cerebellum.
FUNCTION OF CEREBELLUM:
• Basic function of cerebellum is synergism i.e.
activity of agonists and antagonists is
coordinated.
• It controls the timing of turn on signals to
agonists and simultaneous turn off signal to
the antagonists at the start of movement and
then to control the timing of turn off signal to
agonists and simultaneous turn on signal to
antagonists at the end of movement.
FUNCTIONS OF CEREBELLUM
• Lateral Zone:
• It has connections with motor cortex. It also called as cerebrocerebellum.
It is concerned with palnning and programming of movements.
Cerebellum does not initiate movement but controls sequence and timing
of successive movements that lead to smooth progression from one
movement to next.
• Lateral zone has extra motor function.
• Predictive Function: it helps individual to predict how rapidly movement
will occur.
• Intermediate Zone:
• This part receives impulses from the proprioceptors. It compares the
intended plan of movement with actually performed movement,
especially of distal parts of limbs. So it acts as a comparator.
• If there is any discrepancy from the intended plan of movement,
corrective signals are sent to motor cortex to correct it.
• It also controls the rate, range, direction and
force of movement.
• It has a damping function that it prevents the
pendular movements and tremors.
• It also controls the ballistic movements such as
movements of fingers during typing and
movements of eyes during reading. Similarly
movements of eyes of person sitting in moving
vehicle looking outside.
• This intermediate zone has got connections with
spinal cord, it ias also called spinocerebellum
• Vermis and Floculonodular Lobe:
• It has got connections with the vestibular system.
This is also known as vestebulocerebellum.
• This part is concerned with the control of
posture, equilibrium and also eye movements.
• It is also related to the motion sickness. sickness.
• It also controls the stretch reflex and muscle tone
CEREBELLAR DISEASE
• It occurs when the lesion involves cerebellar cortex and one or more deep
cerebellar nuclei. In cerebellar disease there is no muscle paralysis and no
sensory loss.
• Ataxia: incoordinated movements due to errors in the control of rate,
range, force and direction of movements.
• Asynergia: normally there is synergism between agonists and antagonists.
This is lost in cerebellar disease.
• Dysmetria and Past pointing: dysmetria is inability to control range of
movement. Past pointing is a manifestation of dysmetria. In it the hand
overshoots the intended mark.
• Dysdiadokokinesia or Adiadokokinesia: inability to perform rapid
opposite, alternate movements like rapid suppination and pronation.
• Gait and Posture: there is staggering or drunken gait. The patient walks on
a wide base. The head of the patient is rotated and flexed towards the
affected side. Shoulder on the affected side is lower as compared to the
other side.
• Action or Intention Tremors: Tremors are absent at rest and these
appear when the patient performs voluntary actions.
• There is Slurred or Scanned Speech due to dysarthria which is
incoordinate contractions of muscles involved in phonation and
articulation.
• Rebound phenomenon: the patient is unable to stop a movement
promptly which is due to loss of influence over the stretch reflex.
• Decomposition of movements: the patient is unable to perform
actions involving simultaneous movements at more than one joint.
Movements are broken into components.
• Nystagmus: rhythmic osscilatory movements of eye especially
when eyes are fixed to one side.
• Hypotonia: because of loss of facilitatory affect on stretch reflex.
• There is pendular knee jerk.