Cerebellum dr.gosai

Ojvensha E learning Resources-Prepared by Dr.B.B.Gosai

Cerebellum (*****Very Important Long Question)

Introduction:

Cerebellum is the part of Hindbrain responsible for maintenance of tone, posture, equilibrium and coordination of coarse and fine movements.

Location:

Infratentorial compartment of posterior cranial fossa of cranial cavity.

Shape: Ovoid.

Parts:

Two cerebellar hemisphere connected in the midline by Vermis.

External Features:

Whole of the surface of cerebellum contains thin paper like folds known as Folia.

Features on Superior surface:

Anterior cerebellar notch: Wide and separated from brainstem by cavity of fourth ventricle.

Posterior cerebellar notch: Narrow and occupied by Falx cerebella

Primary fissure (Fissura Prima): “V” shaped fissure separating anterior and middle (Posterior) lobe of cerebellum.

Superior vermis: Elevated midline part between two cerebellar hemispheres.


(Draw this diagram- with red marked structures)

Features on Inferior surface:

Anterior cerebellar notch: Wide and separated from brainstem by cavity of fourth ventricle.

Posterior cerebellar notch: Narrow and occupied by Falx cerebella

Posterolateral fissure: separating middle (Posterior) and flocculonodular lobe of cerebellum.

Inferior vermis: Elevated midline part between two cerebellar hemispheres. It is located in the depression known as Valleculum

Tonsil of cerebellum: Rounded bulging part of Middle(Posterior) lobe.

Superior surface

Inferior surface Inferior vermis in Valeculum

Posterolateral fissure

Posterior cerebellar notch

Anterior cerebellar notch


Superior and Inferior surface is separated by Horizontal fissure.

(Draw this diagram- to show arbor vetae cerebelli)

Internal Features:

Cerebellar Cortex: Outer covering gray matter.

White Matter: Inner white matter.

Intracerebellar nuclei: embedded in the white matter are masses of gray matter.

The pattern seen due to gray and white matter gives an appearance like branches of tree and is known as Arbor vetae cerebelli.

Arbor vetae cerebelli


(Draw this diagram- with red labels for lobes)

Lobes of cerebellum: (*****Important – Short note and Viva) There are three lobes of cerebellum:

1. Anerior lobe

2. Middle (Posterior) lobe

3. Flocculonodular lobe

Flocculonodular lobe:

1. Located in front of posterolateral fissure

2. It is part of archecerebellum (Oldest in evolution)

3. Its nucleus is Fastigeal nucleus

4. Its connections are vestibular.

5. Function: Maintenance of Equilibrium

Anterior lobe:

1. Located in front of primary fissure

2. It is part of paleocerebellum (middle in evolution)

3. Its nuclei are Globose Nucleus and Emboliformis nucleus

4. Its connections are Spinal.

5. Function: Maintenance of Tone, posture and coordination of coarse movements


Middle (Posterior) lobe:

1. Located Between primary fissure and Posterolateral fissure

2. It is part of Neocerebellum (Recent –New in evolution)

3. Its nucleus is Dentate nucleus

4. Its connections are cortical.

5. Function: Coordination of fine movements

(No need to draw this diagram- only for understanding)

Nuclei of cerebellum: (*****Important – Viva) There are four nuclei of cerebellum:

1. Nucleus fastigius (Fastigeal nucleus) : for the flocculonodular lobe and responsible for maintenance of equilibrium

2. Nucleus globosus (Globose nucleus): for the Anterior lobe and responsible for maintenance of tone, posture and coordination of coarse movements

3. Nucleus Emboliformis (Emboliformis nucleus): for the Anterior lobe and responsible for maintenance of tone, posture and coordination of coarse movements

4. Nucleus Dentatus (Dentate nucleus): Largest crumpled bag shaped nucleus for Middle lobe and responsible for coordination of fine movements.


Microscopic anatomy of cerebellum: (*****Important –Viva) There are three layers in the cortex of cerebellum:

1. Molecular layer: pale and contain dendrites of Purkinje cells and basket and stellate cells

2. Purkinje cell layer: single layer of flask shaped Purkinje cells.

3. Granular layer: contain Granular cells and Golgi cells

There are two types of fibers coming to cerebellum:

1. Climbing fibers: Olivocerebellar tract from olivary nuclei going up to molecular layer climbing on the dendritic tree of Purkinje cells. These fibers are responsible fine and focused effect due to one to one relation with Purkinje cells.

2. Mossy fibers: All other tracts coming to cerebellum synapse with Granular cells in Granular layer and Granular cells in turn synapse by “T” division of Axon to multiple Purkinje cells and hence are responsible for diffuse effect.




Connections of cerebellum:

(*****Important – Short note and Viva)

Cerebellum is connected to parts of central nervous system by three bundles of fibers known as Cerebellar peduncle:

1. Superior cerebellar peduncle

2. Middle cerebellar peduncle

3. Inferior cerebellar peduncle


(Draw this Diagram for the long question and short note)


Inferior cerebellar peduncle: (*****Important – Short note) 1. It connects medulla oblongata and cerebellum

2. It forms inferolateral boundary of floor of fourth ventricle

Fibers in the Inferior cerebellar peduncle

Afferent fibers:

1. Posterior spinocerebellar tract: it is uncrossed fibers from spinal cord to cerebellum and carries unconscious joint position sensation.

2. Vestibulocerebellar tract: it is uncrossed fibers from vestibular nuclei to cerebellum and responsible for maintenance of equilibrium.

3. Olivocerebellar tract: It is Crossed fibers from contralateral Olivary nuclei to cerebellum and concerned with motor inputs from cortex (Cortico-olivocerebellar tract)

4. Cuneocerebellar tract: from accessory cuneate nucleus to cerebellum

5. Anterior external arcuate fibers from arcuate nucleus to cerebellum

6. Stria medullaris: diverged fibers from arcuate nucleus to cerebellum passing through floor of fourth ventricle

7. Reticulocerebellar fibers from reticular formation to cerebellum

Efferent fibers:

1. Cerebellovestibular tract: it is fibers from fastigeal nucleus to vestibular nuclei.

2. Cerebelloreticular fibers to reticular formation.

Middle cerebellar peduncle: (****Important – viva) 1. It connects pons and cerebellum

2. It continuation of pontocerebellar tract of the pons to cerebellum

Fibers in the Middle cerebellar peduncle

Afferent fibers:

1. Pontocerebellar tract: it is crossed fibers from pontine nuclei of pons to cerebellaum. It is part of fibers from cortex (Cortico-ponto-cerebellar tract)


Superior cerebellar peduncle: (***Important – viva) 1. It connects midbrain and cerebellum

2. It forms superolateral boundary of floor of fourth ventricle

Fibers in the superior cerebellar peduncle

Afferent fibers:

1. Anterior spinocerebellar tract: They are cross in spinal cord and enter the superior cerebellar peduncle and again cross in the cerebellum via commissure of vermis (they double cross to reach the same side they come from spinal cord).

Efferent fibers:

1. Dentatothalamocortical fibers: They are crossed fibers from dentate nucleus to thalamus and after relay in thalamus reach to cortex of cerebrum.

2. Cerebellorubral fibers (Globose-Emboliformis-Rubral fibers) : They are crossed fibers from globose and emboliformis nuclei of cerebellum to red nucleus of midbrain.

3. Olivocerebellar tract: It is Crossed fibers from contralateral Olivary nuclei to cerebellum and concerned with motor inputs from cortex (Cortico-olivocerebellar tract)








Functions of cerebellum: (*****Important – Viva) 1. Cerebellum is compare inputs from spinal and cortical levels and hence also known as

comparator.

2. It controls activities of ipsilateral side (same side) of body .

3. It responsible for maintenance of equilibrium

4. It responsible for maintenance of tone and posture

5. It responsible for Coordination of coarse and fine movements

Applied Anatomy of Cerebellum: (*****Important – Viva)

Cerebellar syndrome:

Damage to cerebellum in degeneration in old age or compression by tumor or vascular lesions leads to :

1. Hypotonia: reduced tone of muscles.

2. Atonia: Loss of tone of muscles (Muscles are soft and flaccid).

3. Loss of posture: Tested by Asking patient to touch the tip of nose by tip of finger (Past-pointing test). In cerebellar disease patient either undershoot or overshoot the tip of nose.

4. Loss of equilibrium: Tested by Romberg’s test: Patient standing erect sways to the side of lesion. Also can be tested by asking to walk on straight line and he will deviate to the side of lesion.

5. Cerebellar gait: Due to loss of equilibrium and posture person will walk like a drunkard.

6. Intention tremors: Vibratory movements of the part when person intends to perform movement (For example buttoning of clothes) but tremors are absent at rest (Tremors at rest are seen in Parkinson’s disease)

7. Dysdiadokokinesis: Loss of rapid alternating movements for example pronation and supination.

8. Dysarthria: Difficulty in speech

9. Cerebellar nystagmus: Abnormal oscillatory movements of eyeball.

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Cerebellum dr.gosai