Cerebellum

Physiology

DEFINITION• The cerebellum ( Latin word means little brain)

is the region of brain that plays an important role in motor control.

Location• The cerebellum is located below the cerebrum

at the rear of the skull.

Anatomy

• Main Parts• Vermis• Two hemispheres

• Fissures• Primary fissure• Horizontol fissure• Posterior fissure

• Lobes• Anterior lobe• Posterior lobe• Flocculondular lobe

Horizontal fissure

verm

is

Primary fissure

Anterior

lobe

Posterior lobe

Hemisphere

VERMIS• The region of the cerebellum lying between and

connecting the two hemispheres.• It is composed of nine parts.

Vermis

CEREBELLAR HEMISPHERES• These are the extended portions on either side of the vermis.

Each hemisphere has two portions:1. Lobulus ansiformis or ansiform lobe :

It is the larger portion of the cerebellar hemisphere.2. Lobulus paramedianus or paramedian lobe:

It is the smaller portion of the cerebellar hemisphere

LOBES1. Anterior lobe :

This include lingula, central lobe and culmen. It is separated by posterior lube by primary fissure.

2. Posterior lobe :It consists of lobulus simplex , declive , tuber , pyramid , uvula , paraflocculi and the two portion of hemispheres ansiform lobe and paramedian lobe.

• Flocculonodular lobe :It includes and the lateral extension on either side called floccules. it is separated from rest of the cerebellum by posteolateral fissure.

FUNCTIONAL AND PHYLOGENETIC SUBDIVISION• Vestibulocerebellum :

It includes flocculonodular lobe that forms the vestibulocerebellum

• Spinocerebellum :It includes lingula,central lobe,lobulus simplex,declive,tuber,pyramid,uvula and para flocculi and medial portions of lobulus ansiformis and lobulus paramedians.

• Corticocerebellum : It includes the lateral portions of lobulus ansiformis and lobulus paramedians

FUNCTIONAL AND PHYLOGENETIC SUBDIVISION

It maintains the muscle tone and adjustment of muscle contraction during movement.It also regulates posture and equilibrium.

Damping actionControl of ballistic movementTiming and programming the movements, Servomechanism Comparator function

It regulates tone.It regulates posture and equilibrium by receving impulses from vestibular apparatus.

Vestibulocerebellum/Archicerebellum

Spinocerebellum/Paleocerebellum

Cerebrocerebelum/neocerebellum

Anterior Lobe

Posterior Lobe

Flocculo-Nodular Lobe (FN lobe)

Primary fissure

FUNCTIONAL ANATOMY OF CEREBELLUM

• Gray matter :Cerebellum is made up of outer gray matter or cerebellar cortex.

• White matter :Cerebellum is made up of inner white matter.

CLINICAL ABNORMALITIES OF CEREBELLUM

DISTURBANCE IN TONE AND POSTURE 1. ATONIA AND HYPOTONIA :

• Atonia is the loss of tone.• Hypotonia is the reduction of the tone.

Cerebellar lesion causes atonia and hypotonia.During this the facilitatory impulses to gamma motor neurons via spinal cord is loss.

2. ATTTITUDE :Attitude of body changes during cereberall lesion:• Rotation of head toward opposite side.• Lowering of shoulder on the same side.

3. DEVIATION MOVEMENT : It is the lateral deviation of arms when both the arms are

stretched and held in front of the bodies.

DISTURBANCE IN EQUILIBRIUM• WHILE STANDING :

• The legs are spread during standing provide a broad base and body sways side to side with the oscillation of head.

• WHILE MOVING - GAIT :• Gait means the manner of walking.In cerebellar lesion a reeling

and drunken like gait is observed.

DISTURBANCES IN MOVEMENTS• ATAXIA :

• It is lack of coordination of movements.• ASTHENIA :

• It refers to the weakness of muscles and slowness of muscles.• Asynergia :

• It is the lack of coordination between different group of muscles.• Dysmetria :

• It is inability to check the exact strength and duration of muscular contractions required for voluntary act. While reaching an object the arm may be overshoot or it may be fall of the object.

• Astasia :• It is charactrized by unsteady voulantary movements.

• Dysathria :• Incoordination of various muscles and structures involved in

speech.

REFERENCES• Books

• Essential of Medical Physiology By Jaypee• Medical Physiology By Guyton and Hall• Medical Physiology William F. Ganong.• Clinical neuroanatomy by Richard S. Snell

• Images• http:// www.google.com• http://www.adamimages.com/Illustration/SearchResult/1/cerebellum