CORTICOCEREBELLUM

CORTICOCEREBELLUM

(NEOCEREBELLUM)

Corticocerebellum is the largest part of cerebellum. Because of its connection with cerebral cortex, it iscalled corticocerebellum or cerebrocerebellum. It is phylogenetically newer part of cerebellum. So, it is also called neocerebellum. It is concerned with planning, programming and coordination of skilled movements.

COMPONENTS

Corticocerebellum includes the lateral portions of cerebellar hemispheres.

CONNECTIONS

Afferent Connections

1. Pontocerebellar tract

Pontocerebellar tract arises from pontine nuclei, crosses the midline and enters corticocerebellum via

middle cerebellar peduncle. It is the largest tract in the body having about 20 million nerve fibers.

Pontocerebellar tract is also called the corticopontocerebellar circuit. Because, it receives signals from

motor area of cerebral cortex and conveys those signals to corticocerebellum. It helps the cerebellum in planning the movements initiated by the cerebral cortex.

2. Olivocerebellar tract

Olivocerebellar tract arises from the inferior olivary nucleus situated in medulla. It crosses the midline

and enters corticocerebellum via inferior cerebellar peduncle of the opposite side. There it terminates on

the dentate nucleus and cerebellar cortex. This tract is formed by climbing fibers.

Inferior olivary nucleus receives impulses from brainstem, spinal cord and cerebral cortex and conveys

these impulses to the corticocerebellum through the olivocerebellar tract.

Efferent Connections

Output signals from corticocerebellum are relayed mainly through the dentate nucleus. Fibers from dentate nucleus pass through superior cerebellar peduncle, cross the midline and form decussation with the fibers of opposite side. After forming the decussation, these

fibers divide into two tracts:

1. Dentatothalamic tract

2. Dentatorubral tract.

 Dentatothalamic tract

After crossing, some of the fibers pass through red nucleus without having any synapse and terminate in

lateral ventral nucleus of thalamus. Tract formed by these fibers is called dentatothalamic tract. Thalamus in turn, projects into the motor area of cerebral cortex via thalamocortical fibers.

2. Dentatorubral tract

Remaining fibers terminate in the red nucleus of opposite side as dentatorubral tract. Three tracts arise

from red nucleus:

i. Rubrothalamic tract: From red nucleus, this tract ascends and terminates in lateral ventral

nucleus of thalamus. From here, thalamocortical fibers arise and reach the cerebral cortex.

ii. Rubroreticular tract: It descends down and ends in reticular formation. Reticular formation

projects into spinal cord via reticulospinal tract.

iii. Rubrospinal tract: Red nucleus also projects directly into spinal cord through rubrospinal

tract.

AFFERENT-EFFERENT CIRCUIT (CEREBROCEREBELLO-

CEREBRAL CONNECTIONS)

Afferent-efferent circuit is an important neuronal pathway, involved in cerebellar control of voluntary

movements, initiated by the motor area of cerebral cortex. This pathway includes two tracts:

1. Cerebropontocerebellar tract

2. Dentatorubrothalamocortical tract.

1. Cerebropontocerebellar Tract

Fibers from motor areas 4 and 6 in frontal lobe of cerebral cortex enter the pontine nuclei. These fibers are called corticopontine fibers . From pontine nuclei, the pontocerebellar fibers arise and pass

through middle cerebellar peduncle of the opposite side and terminate in the cerebellar cortex. This pathway is called the cerebropontocerebellar tract.

2. Dentatorubrothalamocortical Tract

Cerebellar cortex is, in turn, connected to the dentate nucleus. Fibers from the dentate nucleus pass via

superior cerebellar peduncle and end in red nucleus of opposite side. These fibers are called dentatorubral fibers. From red nucleus, the rubrothalamic fibers go to thalamus. Thalamus is connected to areas 4 and 6 in motor cortex of cerebrum by thalamocortical fibers. This pathway is called dentatorubrothalamocortical tract.

FUNCTIONS

Corticocerebellum is concerned with the integration and regulation of well-coordinated muscular activities. It is because of its afferent-efferent connection with cerebral cortex through the cerebro-cerebello-cerebral circuit. Apart from its connections with cerebral cortex, cerebellum also receives feedback signals from the muscles through the nerve fibers of proprioceptors.

 

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