Cerebellum 1

Objectives• Identify the major lobes and regions of cerebellum.• Summarize the structure of the cerebellar cortex• Identify the deep cerebellar nuclei and their connections.• List the afferent and efferent connections of the

cerebellum and their arrangement in cerebellar peduncles.• Describe the major functions of the cerebellum and how

each side of the cerebellum controls the ipsilateral side of the body.

• Explain the effects of lesions of cerebellum and motor disorder associated with cerbellar lesions.

CEREBELLUM

• ORIGIN :From the Hindbrain.• Position :Lies behind Pons & Medulla separated from them by Fourth ventricle.Situated in the posterior cranial fossa

THE CEREBELLUMIt is covered by

tentorium cerebelli CONNECED TO THE

BRAIN STEM BY: Inferior, Middle & Superior Cerebellar Peduncles.

EXTERNAL FEATURES

It consists of two Cerebellar Hemispheres joined in midline by the Vermis.

Its surface is highly convoluted forming the Folia, separated by Fissures.

• Folia: Transversely oriented gyri• 3 lobes in each hemisphere: Anterior, Posterior, Flocculonodular • Neural arrangement: Gray matter (Cortex), White matter (Internal),• Arbor vitae (tree of life): distinctive treelike pattern of the white

matter

EXTERNAL FEATURES

Folium

Cerebellum

Regulation of muscle tone,

coordination of skilled voluntary

movement

Planning and initiation of

voluntary activity

Maintenance of balance, control

of eye movements

Vestibulocerebellum

Spinocerebellum

Cerebrocerebelum

Anterior Lobe

Posterior Lobe

Flocculo-Nodular Lobe (FN lobe)

Folia

Primary fissure

ANATOMICAL SUBDIVISION

1. Anterior lobe: in front of primary fissure, on the superior surface.2. Posterior (middle) lobe: behind primary fissure (Between Primary &

Secondary fissures).3. Flocculonodular lobe: in front of secondary (Posterolateral) fissure ,

on the inferior surface .

Anterroinferior Surface

Superior Surface

LOBES OF CEREBELLUM

Divisions of lobesAnatomicalFlocculonodular lobeAnterior lobePosterior lobe

Anterior lobe

Posterior lobe

Flocculonodular lobe

Inferior surface

Superior surface

Anterior lobe

Posterior lobe

Fourth ventricle

Arbor vitae cerebelli

Arbor vitae

•In latin “ tree of life” it is the white matter of cerebellum. It is so called because of the tree like appearance.It brings sensory and motor sensations to and from cerebellum.

1. Outer grey matter: cerebellar cortex.2. Inner white matter: cerebellar medulla.3. Deeply seated nuclei in white matter: from medial to lateral:• Fastigeal nucleus.• Globose nucleus.• Emboliform nucleus.• Dentate nucleus: largest one.

Structure of the cerebellum

CEREBELLAR CORTEX

Divided into 3 layers:

1. Outer Molecular layer

2. Intermediate Purkinje cell layer

3. Inner granular layer

Cerebellar MedullaConsists of three types of nerve fibres in the white matterA. Axons of purkinje cells The final output of the cerebellar

cortex. The only axons to leave cerebellar cortex to end in deep cerebellar nuclei specially dendate nucleus.

B. Mossy fibres Originate in all the cerebellar

afferent tracts apart from inferior olive. They end in the granular layer.

C. Climbing fibres Originate in the inferior olive of

the medulla. They end in the molecular layer

CEREBELLAR MEDULLAAFFERENT FIBRES: Climbing fibres: from

inferior olivary nucleus, relay to purkinje cells

Mossy fibres: rest of fibres:

1. From vestibular nuclei2. From spinal cord3. From pons• They relay to granule cells

which in turn relay to purkinje cells

CEREBELLAR MEDULLA Axons of Purkinje Cells

are the only axons to leave the cortex to medulla:

1. The great majority of axons do not leave cerebellum & end in deep cerebellar nuclei, specially Dentate nucleus.

2. Some of axons leave cerebellum as efferent fibres.

CEREBELLAR MEDULLAEFFERENT FIBRES: Most of efferent fibres

are axons of deep cerebellar nuclei.

Main Efferents go to:1. Vestibular nuclei2. Red nucleus3. Ventral lateral nucleus

of thalamus.

FUNCTIONAL SUBDIVISIONS OF

THE CEREBELLUM

Functional (Evolutionary) divisions

Paleocerebellum

Neocerebellum

Archicerebellum

ARCHICEREBELLUM

• Vestibular Part of cerebellum: Flocculonodular lobe.

Green = Archi-cerebellum, Blue= Paleo-cerebellum. Pink= Neo-cerebellum.

ARCHICEREBELLUM Nuclei Related: Fastigeal Afferents: from : 1- Vestibular apparatus of internal ear via vestibulo-cerebellar tracts2- Vestibular nuclei (Vestibulocerebellar fibres),(through ICP) Efferents: to Vestibular

nuclei (through ICP) Function: controls

Balance (via vestibulospinal & reticulospinal tracts).

PALEOCEREBELLUM

• Spinal Part of cerebellum: Vermis & Paravermis

Green = Archi-cerebellum, Blue= Paleo-cerebellum. Pink= Neo-cerebellum.

PALEOCEREBELLUMNuclei Related: globose &

emboliform

Afferents: from spinal cord (dorsal & ventral spinocerebellar tracts through ICP & SCP, respectively)

(proprio-ceptive impulses from Ms.& tendons )

Efferents: to red nucleus (through SCP)

Function: influences posture & muscle tone (via Rubrospinal tract).

NEOCEREBELLUM• Cerebral Part of

cerebellum: Rest of Cerebellum.

NEOCEREBELLUMNuclei Related: DentateAfferents: It receives afferent

impulses from the cerebral cortex+ pons Via cerebro-ponto- cerebellar pathway. (Pontocerebellar fibres) (through MCP)

Efferents: to Red nucleus but mostly to Ventral Lateral Nucleus of Thalamus (through SCP) then to motor cortex

Function: coordination of voluntary movements (via descending corticospinal & corticobulbar tracts).

Classification by development

Archicerebellum Paleocerebllum Neocerebellum

Classification by Afferent Connection

Vestibulocerebellum Spinocerebellum Pontocerebellum

Classification by Efferent Connection

Vermis Paravermal Region Cerebellar Hemisphere

ArchicerebellumNodulusArchicerebellumflocculusPalaeocerebellum

Neocerebellum

Spinocerebellum

Pontocerebellum

Vestibulocerebellum

Summary of classification

Maintenance of Equilibrium - balance, posture, eye movement

Coordination of half-automatic movement of walking and posture maintenace - posture, gait

Adjustment of Muscle Tone

Motor Leaning – Motor Skills

Cognitive Function

Functions of cerebellum

CEREBELLAR LESIONS

• MIDLINE LESION: Loss of postural control.• UNILATERAL LESION: IPSILATERAL “Cerebellar

ataxia” .Causes :1. Incoordination of arm: intention tremor (on

performing voluntary movements)2. Incoordination of leg: unsteady gait3. Incoordination of eye movements: nystagmus: rapid

jerky eye movements4. Slowness of speech: dysarthria Staccato speech

Cerebellar Ataxia

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

Remember:

IPSILATERAL

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 stood on the floor.

SUMMARY

Anatomically, the cerebellum is divided into: anterior, posterior & flocculonodular lobes.

Developmentally & functionally, it is divided into: archi- paleo- & neocerebellum.

Archicerebellum (flocculonodular lobe) is the oldest part of cerebellum, related to fastigeal nucleus, connected to vestibular nuclei & concerning for control of body balance.

SUMMARYPaleocerebellum (vermis & paravermis) is related

to globose & emboliform nuclei, connected to spinal cord & red nucleus & concerned with regulation of posture & muscle tone.

Neocerebellum (most of human cerebellum) is related to dentate nucleus, connected to pons, thalamus. Its final destination is to motor cortex. It is concerned with coordination of voluntary movements.

Cerebellar lesions lead to ipsilateral incoordination (ataxia).