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Page 1: Cerebellum ppt
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PREPARED BY KANCHAN SHARMA (BPT 4TH YEAR, AMITY UNIVERSITY)

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Located dorsal to the Pons and Medulla Makes up 11% of the brain’s mass Cerebellar activity occurs

subconsciously Provides precise timing and appropriate

patterns of skeletal muscle contraction Programming ballistic movements

Acts as comparator for movementsComparing intended and actual movement

Correction of ongoing movements Internal & external feedback

Deviations from intended movement Motor learning

Shift from conscious ---> unconscious Folia: Transversely oriented gyri

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Anatomy of the Cerebellum2 symmetrical hemispheres connected medially by the Vermis 3 lobes in each hemisphere: Anterior, Posterior, Flocculonodular (FN)Neural arrangement: Gray matter (Cortex), White matter (Internal), Scattered cerebellar nuclei: dentate, globose, emboliform, fastigial Arbor vitae (tree of life): distinctive treelike pattern of the white matter

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•  located in the posterior cranial fossa.

• The fourth ventricle, pons and medulla are in front of the cerebellum.• separated from the overlying cerebrum by a layer of leathery dura mater,

the tentorium cerebelli; all of its connections with other parts of the brain travel through the pons. divided into two hemispheres; it also contains a narrow midline zone (the vermis). A set of large folds divide the overall structure into 10 smaller "lobules".

• Because of its large number of tiny granule cells, the cerebellum contains more neurons than the total from the rest of the brain.

• The unusual surface appearance of the cerebellum conceals the fact that most of its volume is made up of a very tightly folded layer of gray matter: the cerebellar cortex.

• Each ridge or gyrus in this layer is called a folium. Underneath the gray matter of the cortex lies white matter, made up largely of myelinated nerve fibers running to and from the cortex.

• Embedded within the white matter—which is sometimes called the arbor vitae (Tree of Life) because of its branched, tree-like appearance in cross-section—are four deep cerebellar nuclei, composed of gray matter.

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Cerebellum

Regulation of muscle tone,coordination of skilled voluntary movement

Planning and initiation of voluntary activity

Maintenance of balance, control of eye movements

VestibulocerebellumSpinocerebellum

Cerebrocerebelum

Anterior Lobe

Posterior Lobe

FN lobe

Folia

Primary fissure

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Cerebellum: the StructureInputs to the cerebellar cortex: Climbing fibers & Mossy fibersClimbing fibers: originate in the inferior olive of the medullaMossy fibers: originate in all the cerebellar afferent tracts apart from inferior olivePurkinje cells: The final output of the cerebellar cortex

3 Layered CerebellarCortex

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DIAGRAM SHOWING HISTLOGICAL COMPONENTS OF CEREBELLUM

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Most Important Neuronal Connections 1. Mossy fibers are excitatory to granule cells.

2. Climbing fibers are excitatory to Purkinje cells.

3. Both types of afferent fibers send collaterals to the CBL subcortical nuclei.

4. Granule cells, via their axons, the parallel fibers, are excitatory to Purkinje, basket, stellate, and Golgi cells. Glutamate is the neurotransmitter.

5. Each parallel fibers run longitudinally for several millimeters along a cerebellar folium, synapsing on a long strip of Purkinje cells.

6. Basket and stellate cells are inhibitory to Purkinje cells.

7. Axons of basket cells are perpendicular to the parallel fibers in the plane of the CBL cortex.

8. Purkinje cells are inhibitory to nuclear cells.

9. Nuclear cells are excitatory to their target cells (UMNs or thalamic neurons).

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Cerebellar PedunclesThree paired fiber tracts connect the cerebellum to the brainstem:♦ Superior peduncles connect the cerebellum to the midbrain;♦ Middle peduncles connect the cerebellum to the pons and to the axis

of the brainstem;

♦ Inferior peduncles connect the cerebellum to the medulla.

CerebellarPeduncles

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Cerebellar Peduncles

Superior peduncles (to the midbrain):Fibers originate from neurons in the deep cerebellar nuclei & communicates with the motor cortex via the midbrain and the diencephalon (thalamus)Middle peduncles (to the Pons):Cerebellum receives information advising it of voluntary motor activities initiated by motor cortexInferior peduncles (to the medulla):Afferents conveying sensory information from muscle proprioceptors throughout the body & from the vestibular nuclei of the brainstem (Spinal cord)

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Cerebellar Inputs

Pons Cerebellum

Vestibularinputs

Cerebral cortex

InferiorOlive

SpinalCord

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The cerebellar outputs Cerebellar cortex

Deep nuclei

Thalamus VestibularNuclei

InferiorOlive

RedNucleus

CerebralCortex

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Inputs and outputs of the Cerebellum

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Functional regions of cerebellum Divided into three regions:• vestibulocerebellum

(archicerebellum)

• the spino-cerebellum (paleocerebellum)

• the cerebrocerebellum (neocerebellum)

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Vestibulocerebellum• consists of the flocculonodular lobe ,parts of the vermis.• receives input mainly from the vestibular system. • richly interconnected with UMNs of the medial brainstem

motor pathway, especially those in the vestibular nuclei.• responsible for coordination of movements involving whole

body equilibrium and posture.

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The Spinocerebellum

• receives information form the spinal cord . • comprises the entire anterior lobe and parts of posterior lobe.• concerned with control of the axial and limb mucscles and postural reflexes.

The Cerebrocerebellum

• inputs arrive mainly from cerebral cortex via the pontine nuclei. • Because of this fact it is also sometimes called the pontocerebellum. • concerned with skilled voluntary movements.

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Functions of the Cerebellum

• control of body posture and equillibrium.

• control of muscle tone and stretch relfexes.

• control of involunatry and voluntary movements.

• provide for smooth, coordinated, synegistic movement .

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Cerebellar Lesions

Damage to the vestibulocerebellum 

• show up as a loss of equilibrium and an  altered walking gait , • With a wide stance that indicates difficulty in balancing.• eye movement disorders like Nystagmus.

Damage to cerebrocerebellum

 problems with skilled voluntary and planned movements. causes errors in the force, direction, speed and amplitude of movements. Some manifestations include:• hypotonia •  dysarthria • dysmetria • Dysdiadochokinesia• intention tremor

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 Damage to spinocerebellum

• Tends to cause gait impairments and other problems with leg coordination.

• Damage to the lower part is more likely to cause uncoordinated or poorly aimed movements of the arms and hands, as well as difficulties in speed. This complex of motor symptoms is called ataxia.

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HypotoniaThe muscle tone is either completely lost (atonia) or markedly decreased (hypotonia) on the affected side. Therefore, the muscles feels soft (or loose) and the limb moves to to and fro freely.

It usually accompanies acute hemispheric lesions .

• less often seen in chronic lesions

• Ispilateral to the side of a cerebellar lesion

• More noticeable in upper limbs and proximal muscles.

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Ataxia• result from defective timing of sequential contractions of agonist and

antagonist muscles due to disturbance in the smooth performance of voluntary motor acts.

• movements errantic in speed, range, force, and timing.

• affects limbs, trunk, gait, may be acute onset,episodic or progressive.

• includes: asynergia(lack of synergy of various muscles while performing complex movements. Movements are broken up into isolated, successive parts-- decomposition of movement) dysdiadokinesia (impaired performance of rapidly alternating movement) past pointing dysmetria (abnormal excursions in movement)

Truncal instability -falls in any directions. Wide based stance and gait characterized by staggering and impaired tandem walking.

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TRUNCAL ATAXIAATAXIC GAIT ( DRUNKEN GAIT )

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Cerebellar Dysarthria• motor speech disorder.

• Abnormalities in articulation and prosody (together or independent).

• “scanning”, “slurring”, “staccato”, “explosive”, “hesitant”, “garbled”

• May result from a generalized hypotonia (disorder of muscle spindle function)

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Intention tremors• Unable to perform smooth

movements.

• If reach for an object, jerky movements accompanied by oscillationg, to and fro tremors that becomes more marked as the hand reaches the object.

• Usually coarse; occur at frequency • of 4-6/sec.

• Occurs during the volunatry movements.

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HORIZONTAL

VERTICAL

TORSIONAL

Nystagmus

Types

• eye movement disorder. • Results in 

reduced or limited vision.

• Due to the involuntary movement of the eye, it is often called "dancing eyes"

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THANK YOU.....