ASHIQ DEPARTMENT OF ANATOMY Cerebellum ASHIQ DEPARTMENT OF ANATOMY

Learning outcomes parts of cerebellum External & internal features of cerebellum. Describe the connections and lesions of cerebellum. Cerebral peduncles

Little Brain The cerebellum was called the “silent” area of the brain because electrical stimulation did not give rise to any : • conscious sensation, or... • any muscle action The cerebellum is a SENSORY structure. • The sensory signals that it receives are not consciously perceived, they are used to modify muscle action.

Cerebellum Latin word – small brain Largest part of hind brain Situated in the posterior cranial fossa, behind pons and medulla .covered by tentorium ceribelli weight- 150 grams Aproxi:100 millions of neuron Shape : Ovoid but constricted in the median plane, Flatened from above downwards, Widest from side to side

Position Lies above and behind the medulla oblongata and pons and occupies posterior cranial fossa. Cerebellum

Parts & surfaces of cerebellum 2 cerebellar hemispheres. Vermis is the cerebellar substance connecting two hemispheres. Surfaces: Has superior & inferior surfaces. Presents anteriorly a notch to lodge pons & medulla.

External features Consists of two cerebellar hemisphere united in the midline by the vermis [ worm].

External features- surfaces Two surfaces Superior surface – is elevated in the midline forms the superior vermis and continuous with cerebellar hemispheres Inferior surface - It is grooved in the midline separating the hemispheres Inferior vermis lies in the deep groove and is limited on each side by vallecula

Fissures of cerebellum Surfaces & vermis of cerebellum are traversed by fissures. Prominent fissures: Fissura prima. Horizontal fissure. Posterolataeral fissure.

Primary Fissure

External feature – fissures and sulci There are numerous transverse fissures They are called as folia There are three important fissures Horizontal fissure It is the junction of superior and inferior surfaces (13) Primary fissure (15) It appears on the superior surface It is ‘V’ shaped with apex directed dorsally It is the junction of anterior two thirds with posterior one third It separates anterior lobe from posterior lobe

Lobes Horizontal fissure Anterior lobe corpus of cerebellar Primary fissure Posterior lobe Horizontal fissure Flocculonodular lobe Posterolateral [dorsolateral] Fissure Retrotonsilar fissure

Fissures & lobes Three deep fissures: Three lobes: Primary fissure Horizontal fissure Posterolateral fissure Three lobes: 1.Flocculonodular lobe flocculus and nodule 2.Anterior lobe 3.Posterior lobe

External feature – cerebellar notches There are two notches Anterior and posterrior Anterior notch it is ‘V’ shaped It lodges pons and medulla Posterior notch It is narrow It lodges falx cerebelli

Posterolateral fissure It is first to appear It appears on the inferior surface in the anterior aspect It separates flocculonodular lobe from rest of cerebellum Nodule is the portion of vermis Flocculli are portions of cerebellar hemispheres

Cerebellum with various parts 1. Crus cerebri 2. Subsrtantia nigra 3. Red nucleus 4. Cerebral aqueduct 5. Tectum 6. Central lobule 7. Culmen 8. Declive 9. Wing of the central lobule 10. Quadrangular lobule 11. Simple lobule 12. Suprior semilunar lobule 13. Horizontal fissure 14. Superior posterior fissure 15. Primary fissure 16. Posterior cerebellar incisure 17. Interpeduncular fossa

Internal structure Gray matter lies externally called cortex White matter lies internally called medulla There are central cerebellar nuclei embedded in the medulla

Arbor vitae The surface of cerebellum is laminated in appearance Each is called folia Deep inside folia there is white matter [like Branches of the Tree]called arbor vitae They are capped by gray matter called as cortex

Functional divisions Three parts: • Vestibulocerebellum (archicerebellum), responsible for balance and eye movements. • spinocerebellum (paleocerebellum). • Cerebrocerebellum (neocerebellum).

Three functional divisions Vestibulocerebellum Archicerebellum Flocculonodular lobe +Lingula Spinocerebellum Paleocerebellum Vermis and intermediate zone Cerebrocerebellum Neocerebellum Lateral zone Vermis Intermediate zone Lateral zone Flocculonodular lobe

Vestibulocerebellum-flocculonodular lobe The flocculus and the nodulus (flocculonodular lobe) - vestibulocerebellum. • Phylogenetically the oldest part.

Spinocerebellum

Cerebrocerebellum

Functional lobes of cerebellum ‘H’ is the anterior lobe – function muscle tone ‘I’ is the posterior lobe – function coordination ‘G’is the flocculonodular lobe – function equilibrium

Connections and function of cerebellum Vestibulocerebellum- Connections: Afferents: receive input from vestibular nuclei and primary vestibular Efferents: projects to the vestibular nucleus → vestibulospinal tract and medial longitudinal fasciculus → motor neurons of anterior horn Function: involved in eye movements and maintain balance.

Connections and function of cerebellum Spinocerebellum- Connnection Afferents: receive somatic sensory information via spinocerebellar tracts - Efferents: Vermis projects to the fastigial nucleus → vestibular nuclei and reticular formation → vestibulospinal tract and reticulospinal tract → motor neurons of anterior horn Intermediate zone projects to the interposed nuclei Contralateral red nucleus → rubrospinal tract →motor neurons of anterior horn Contralateral VI →cerebral cortex→ coticospinal tract→motor neurons of anterior horn. Function: control of muscle tone and coordination of muscle movement on the same side of the body.

Connections and function of cerebellum Cerebrocerebellum- Connection: Afferents: receives input from the cerebral cortex via a relay in pontine nuclei. Efferents: projects to dentate nucleus → primary motor cortex → corticospinal tract → motor neurons of anterior horn. Function: participates in planning movements.

Cerebellar peduncles Three peduncles: There are three peduncles They contain fibers which connect cerebellum with brain stem Inferior cerebellar peduncle connect with medulla and spinal cord, contain both afferent and efferent fibers. Middle cerebellar peduncle connect with pons, contain afferent fibers. Superior cerebellar peduncle connect with midbrain, contain mostly efferent fibers.

Inferior Cerebellar peduncle Inferior cerebellar peduncle connects with – medulla oblongata It consists of mainly afferent fibers The afferent fibers : Posterior spinocerebellar tract Vestibulocerebellar tract Olivocerebellar tract –arises from inferior olivary nucleus Posterior external arcuate fibers Anterior external arcuate fibers Stria medularis Reticulocerebellar Efferemt fibers : Cerebello-olivary Cerebello-vestibular Cerebello-reticular

Middle cerebellar peduncle It connects cerebellum with pons It consists of entirely afferent fibers Afferent fibers arise in the nuclei pontis of the opposite side They are crossed ponto- cerebellar They are the second neurons of cortico-ponto-cerebellar pathway

Superior cerebellar peduncle It connects cerebellum with midbrain It consists of mainly efferent fibers Afferent fibers Anterior spinocerbellar tract Rubrocerebellar Efferent fibers They form the major output They arise in the dentate nucleus They pass to midbrain Decussate with the opposite side Divide into ascending and descending Ascending pass to red nucleus and thalamus Descending end in the olivary nucleus and reticular formation

Deep nuclei of cerebellum nuclei They are deeply placed in the white matter Lateral to medial they are 4 in numbers DEGF D- Dentate E- Emboliformis G – Globosus F- Fastigius

Cerebellar nuclei - fastigius It lies close to the midline The oldest nucleus Associated with archicerebellum

Cerebellar nuclei – globosus and emboliformis They are more recent and are associated with paleocerebellum

Dentate nucleus It is the largest and the chief nucleus It is shaped like a crumpled bag With hilus facing medially Through it most of the supreior cerebellar peduncle emerges It is the most recent nucleus and associated with neocerbellum

Dentate nucleus It receives afferents from the lateral hemispheres And receives collaterals from the mossy and climbing fibers Efferent's pass in the superior cerebellar peduncle Terminate mostly in the red nucleus Dentatorubrospinal patyhway Thalamus Dentatothalamocortical pathway

Deep nuclei of cerebellum Cerebellar cortex Fastigial nucleus Globose nucleus Dentate nucleus Emboliform nucleus White matter

Structure of cerebellum Outer grey matter called the cortex & inner white matter. Deep nuclei are grey matter embedded in the white matter. The cortex (grey matter) is divided into : Outer molecular layer Middle Purkinje cell layer Inner granular layer

Structure of the cerebellum

Histology Cortex is uniform in structure It consists of three layers Molecular layer Purkinje cell layer Granular layer

Molecular layer Molecular layer consists of Stellate and basket cells Dendrites of purkinje and golgi cells Axons of granule cells which are T shaped

Purkinje layer Purkinje cells are large flask shaped cells At the junction of molecular and granule layers They are the principal neurons of cerebellum Dendrites arise from neck and pass into molecular layer Axons arise from bottom and pass through granule layer and end in the cerebellar nuclei

Granular layer Golgi cells lie at the junction of molecular and granular layer Their dendrites pass into molecular layer and axons synapse with granule cells Granular layer consists of numerous granule cells Their axons pass into molecular layer and divide into in T shapes manner

Afferent and efferent fibers of cerebellar cortex Afferent tracts that constitute climbing fibers are mainly olivocerebellar They end in the purkinje cells Most afferent tracts are mossy fibers Mossy fibers end in the granule cells of cerebellum Efferent fibers Are axons of purkinje Which end in the cerebellar nuclei Both mossy and climbing fibers are excitatory In summary of all the cells granule calls are excitatory

Blood supply of cerebellum Arterial supply: Superior surface: Superior cerebellar artery- branch of basilar artery. Inferior surface: Anterior inferior cerebellar artery -branch of basilar artery Posterior inferior cerebellar- branch of vertebral artery Venous drainage: Veins drain into neighbouring venous sinuses.

Cerebellum Function  Maintenance of Equilibrium - balance, posture, eye movement  Coordination of half-automatic movement of walking and posture maintenace - posture, gait  Adjustment of Muscle Tone  Motor Learning – Motor Skills

Balance

Motor Skill Pablo Casals

Clinical Anatomy

Tonsils

Cerebellum Clinical Syndromes Ataxia: incoordination of movement. gait ataxia (unsteady gait). Intention Tremor Hypotonia, Nystagmus Archicerebellar Lesion: medulloblastoma Paleocerebellar Lesion: gait disturbance Neocerebellar Lesion: hypotonia, ataxia, tremor

Posture Gait – Ataxia Tremor

Cerebellar Ataxia a b c d Ataxic gait and position: Left cerebellar tumor a. Sways to the right in standing position b. Steady on the right leg c. Unsteady on the left leg d. ataxic gait d

Cerebellar Medulloblastoma Cerebellar tumors on vermis - Truncal Ataxia - Frequent Falling The child in this picture: - would not try to stand unsupported - would not let go of the bed rail if she was stood on the floor.

Finally remember 3’s

Cerebellum 3 parts - 2 hemispheres and central vermis. 3 functional parts -archicerebellum, paleocerebellum and neocerebellum.. 3 cerebellar peduncles -superior,middle & inferior. 3 layers – outer molecular,middle Purkinje and inner granular. 3 functions - coordination of fine voluntary movements, regulates muscle tone & maintains balance (equilibrium). 4 deep nuclei -dentate,globose,emboliformis & fastigius.

Applied anatomy Loss of equilibrium results in -Staggering or unsteady gait called as cerebellar ataxia Pendular knee jerk due to reflex abnormalities Hypotonia – due to loss of muscle tone there is diminished resistance to passive movement Dysmetria –– it is overshooting the objective -the patient finds difficult to touch his nose called past pointing test

Cerebellar Cognitive Affective Disorder Lesions of the posterior cortex and vermis Impairment of executive functions Planning, verbal fluency, abstract reasoning Difficulties with spatial cognition Visuo-spatial organization, visual memory Personality changes Blunting of affect, inappropriate behaviors Language disorders Agrammatism

Conclusions Cerebellar lesions produce Motor learning Incoordination & errors not weakness Lose ability to anticipate errors Lose ability to correct Motor learning Requires sensory awareness Implemented via the descending cortical and brain stem pathways Cognitive and emotional disturbances Anatomical connections to prefrontal and cingulate cortex (via thalamus) No single function Clearly mostly motor; learning, optimizes Functions may apply to cognitive and emotional behaviors

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