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

THE CEREBELLUM It 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.

EXTERNAL FEATURES 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 Folium

Cerebellum Anterior Lobe Posterior Lobe Primary fissure Anterior Lobe Regulation of muscle tone, coordination of skilled voluntary movement Posterior Lobe Planning and initiation of voluntary activity Flocculo-Nodular Lobe (FN lobe) Maintenance of balance, control of eye movements Vestibulocerebellum Spinocerebellum Cerebrocerebelum Folia

ANATOMICAL SUBDIVISION Superior Surface Anterroinferior Surface Anterior lobe: in front of primary fissure, on the superior surface. Posterior (middle) lobe: behind primary fissure (Between Primary & Secondary fissures). Flocculonodular lobe: in front of secondary (Posterolateral) fissure , on the inferior surface .

LOBES OF CEREBELLUM Divisions of lobes Anatomical Flocculonodular lobe Inferior surface Anterior lobe Divisions of lobes Anatomical Flocculonodular lobe Anterior lobe Posterior lobe Posterior lobe Flocculonodular lobe Superior surface Anterior lobe Posterior lobe

Arbor vitae Arbor vitae cerebelli •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. Fourth ventricle

Structure of the cerebellum Outer grey matter: cerebellar cortex. Inner white matter: cerebellar medulla. Deeply seated nuclei in white matter: from medial to lateral: Fastigeal nucleus. Globose nucleus. Emboliform nucleus. Dentate nucleus: largest one.

CEREBELLAR CORTEX Divided into 3 layers: Outer Molecular layer Intermediate Purkinje cell layer Inner granular layer

Cerebellar Medulla Consists of three types of nerve fibres in the white matter 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. Mossy fibres Originate in all the cerebellar afferent tracts apart from inferior olive. They end in the granular layer. Climbing fibres Originate in the inferior olive of the medulla. They end in the molecular layer

CEREBELLAR MEDULLA AFFERENT FIBRES: Climbing fibres: from inferior olivary nucleus, relay to purkinje cells Mossy fibres: rest of fibres: From vestibular nuclei From spinal cord 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: The great majority of axons do not leave cerebellum & end in deep cerebellar nuclei, specially Dentate nucleus. Some of axons leave cerebellum as efferent fibres.

CEREBELLAR MEDULLA EFFERENT FIBRES: Most of efferent fibres are axons of deep cerebellar nuclei. Main Efferents go to: Vestibular nuclei Red nucleus 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 tracts 2- 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.

PALEOCEREBELLUM Nuclei 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.

NEOCEREBELLUM Nuclei Related: Dentate Afferents: 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).

Summary of classification Classification by development Archicerebellum Paleocerebllum Neocerebellum Classification by Afferent Connection Vestibulocerebellum Spinocerebellum Pontocerebellum Classification by Efferent Connection Vermis Paravermal Region Cerebellar Hemisphere Archicerebellum Nodulus Archicerebellum flocculus Palaeocerebellum Neocerebellum Spinocerebellum Pontocerebellum Vestibulocerebellum

Functions of cerebellum  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

CEREBELLAR LESIONS MIDLINE LESION: Loss of postural control. UNILATERAL LESION: IPSILATERAL “Cerebellar ataxia” .Causes : Incoordination of arm: intention tremor (on performing voluntary movements) Incoordination of leg: unsteady gait Incoordination of eye movements: nystagmus: rapid jerky eye movements 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.

SUMMARY Paleocerebellum (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).