The Cerebellum

Position Lies above and behind the medulla and pons and occupies posterior cranial fossa Its surface is high convoluted, forming folds or folia, being oriented transversely Cerebellum

External features Consists of two cerebellar hemisphere united in the midline by the vermis

External features Three peduncles Inferior cerebellar peduncle －connect with medulla and with spinal cord, contain both afferent and efferent fibers Middle cerebellar peduncle －connect with pons, contain afferent fibers Superior cerebellar peduncle －connect with midbrain, contain mostly efferent fibers

External features Tonsil of cerebellum two elevated masses on inferior surface of hemispheral portion just nearby foramen magnum

Lobes Two deep fissures Three lobs Primary fissure Uvulonodular fissure Three lobs Flocculonodular lobe Anterior Posterior lobe

Lobes Anterior lobe corpus of cerebellar Primary fissure Posterior lobe Flocculonodular lobe Posterolateral fissure

Internal structures White matter Gray matter Cerebellar cortex Cerebellar nuclei Dentate nucleus Fastigial nucleus Emboliform nucleus Globose nucleus White matter

Internal structures Fastigial nucleus Cerebellar cortex Globose nucleus Dentate nucleus Emboliform nucleus medullary center

Deep Nuclei 1. fastigial nucleus 2. globose 3. emboliform 4. dentate

Three functional divisions Vestibulocerebellum Archicerebellum Flocculonodular lobe Spinocerebellum Paleocerebellum Vermis and intermediate zone Cerebrocerebellum Neocerebellum Lateral zone Vermis Intermediate zone Lateral zone Flocculonodular lobe

Cerebellar divisions Spinocerebellum: Vermis Intermediate hem. (Vermis + Intermed. Hem) Control of limbs and trunk Lateral hem. Cerebrocerebellum: Cerebrocerebellum (Lateral hemisphere) Planning of movement+ IVth vent Floculo-nodular lobe Vestibulo-cerebellum (Floculo-nodular lobe) Control of eye & head movements Balance

Connections and function of cerebellum Vestibulocerebellum Connections Afferents: receive input from vestibular nuclei and inner ear. Efferents: projects to the vestibular nucleus → vestibulospinal → motor neurons of anterior horn Function: involved in eye movements and maintain balance

Connections and function of cerebellum Spinocerebellum Connnection Afferents: receive somatic sensory information via spinocerebellar tracts

Efferents: Fastigeal reticular and fastigial vestibular pathways: Vermis projects to the fastigial nucleus → vestibular nuclei and reticular formation → vestibulospinal tract and reticulospinal tract → motor neurons of anterior horn Intermediate zone projects to the interposed nuclei Globose- emboliform-rubral pathway: Contralateral red nucleus → rubrospinal tract →motor neurons of anterior horn Function: play an important role in control of muscle tone and coordination of muscle movement on the same side of the body

Connections and function of cerebellum Cerebrocerebellum Connection Afferents: receives input from the cerebral cortex via a relay in pontine nuclei(corticopontocerebellar pathway) Efferents: (dentothalamic pathway): dentate nucleus → contralateral thalamus → primary motor cortex → corticospinal tract → motor neurons of anterior horn Function: participates in planning movements

summary Cerebellar efferent fibers: Globose-emboliform-rubral pathway Dentothalamic pathway Fastigial reticular pathway Fastigial vestibular pathway

summary Cerebellar afferent fibers: Afferent fibers from cerebral cortex: corticopontocerebellar pathway. Afferent fibers from spinal cord: Anterior and posterior spinocerebellar tracts Afferent fibers from vestibular nerve

Pyramidal Tract and Associated Circuits upper motor neuron UMN Cerebellum BASAL GANGLIA pyramidal tract lower motor neuron UMN

Cerebellum Function  Maintenance of Equilibrium - balance, posture, eye movement  Coordination of movement of walking and posture maintenance - posture, gait  Adjustment of Muscle Tone  Motor Learning – Motor Skills

Balance

Motor Skill Pablo Casals

Cerebellum Clinical Syndromes 1-Ataxia: incoordination of movement - decomposition of movement - tremor - past-pointing 2- dysdiadochokinesia 3-Hypotonia, Nystagmus 4- dysarthria

Posture Gait – Ataxia

Cerebellar Ataxia a b c d 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 d