PARTS OF CEREBELLUM

 

PARTS OF CEREBELLUM

Cerebellum consists of a narrow, worm-like central body called vermis and two lateral lobes, the right and left cerebellar hemispheres.

VERMIS

Vermis of cerebellum is formed by nine parts. Part of vermis on the upper surface of cerebellum is known as superior vermis and the part on lower surface of cerebellum is called inferior vermis.

Nodulus is continued on either side as an elongated and somewhat lobulated structure called flocculus. Nodulus and flocculi are together called flocculonodular lobe. On either side of pyramid, there is another extension named paraflocculus.

 Fissures Present Over the Surface of Vermis

1. Primary fissure between culmen and lobulus simplex

2. Prepyramidal fissure between tuber and pyramid

3. Posterolateral fissure between uvula and nodulus.

CEREBELLAR HEMISPHERES

Cerebellar hemispheres are the extended portions on either side of vermis.

Each hemisphere has two portions:

1. Lobulus ansiformis or ansiform lobe, which is the larger portion of cerebellar hemisphere

2. Lobulus paramedianus or paramedian lobe, which is the smaller portion of cerebellar hemisphere.

DIVISIONS OF CEREBELLUM

Division of cerebellum into different major parts is done

by three methods:

A. Anatomical divisions

B. Phylogenetic divisions

C. Physiological or functional divisions.

ANATOMICAL DIVISIONS

On structural basis, the whole cerebellum is divided into

three portions:

1. Anterior lobe

2. Posterior lobe

3. Flocculonodular lobe.

Anterior Lobe

Anterior lobe includes lingula, central lobe and culmen. It is separated from posterior lobe by primary fissure.

Posterior Lobe

Posterior lobe consists of lobulus simplex, declive, tuber, pyramid, uvula, paraflocculi and the two portions of hemispheres, viz. ansiform lobe and paramedian lobe.

Flocculonodular Lobe

Flocculonodular lobe includes nodulus and the lateral extension on either side called flocculus. It is separated from rest of the cerebellum by posterolateral fissure.

PHYLOGENETIC DIVISIONS

Depending upon phylogeny, the cerebellum is divided

into two divisions:

1. Paleocerebellum

2. Neocerebellum.

Paleocerebellum

Paleocerebellum is the phylogenetically oldest part of cerebellum. It includes two divisions:

i. Archicerebellum, which includes flocculonodular lobe

ii. Paleocerebellum proper, which includes lingula, central lobe, culmen, lobulus simplex, pyramid,

uvula and paraflocculi.

Neocerebellum

Neocerebellum is the phylogenetically newer portion of cerebellum. It includes declive, tuber and the two portions of cerebellar hemispheres, viz. lobulus ansiformis and lobulus paramedianus.

PHYSIOLOGICAL OR FUNCTIONAL DIVISIONS

Based on functions, the cerebellum is divided into three

divisions:

1. Vestibulocerebellum

2. Spinocerebellum

3. Corticocerebellum.

1. Vestibulocerebellum

Vestibulocerebellum includes flocculonodular lobe that forms the archicerebellum.

2. Spinocerebellum

Spinocerebellum includes lingula, central lobe, culmen, lobulus simplex, declive, tuber, pyramid, uvula and paraflocculi and medial portions of lobulus ansiformis and lobulus paramedianus.

3. Corticocerebellum

Corticocerebellum includes lateral portions of lobules ansiformis and lobulus paramedianus.