CEREBELLUM
Connection of the cerebellum The cerebellum has external layer of gray matter (cerebellar cortex ), & inner white matter In the white matter, there are 3 deep nuclei : (a) dentate nucleus laterally ( b) fastigial nucleus medially (c ) interpositus nucleus (formed of the globose & emboliform nuclei ) between the other 2 nuclei Both the afferent & efferent connection of the cerebellum pass via the 3 cerebellar peduncles All afferent fibers relay first mostly at the cerebellar cortex
Con Then the cerebellar cortex discharge to the deep nuclei, from which the efferent fibers originate and leave the cerebellum 1. fastigial nucleus 2. globose nucleus 3. embolif orm nucleus 4. dentate nucleus
Con Functional division of the cerebellum :- Cerebellum is divided into 3 parts : 1. Vestibulocerebellum : this is the oldest part of the cerebellum, and is consist of the flocculonodular lobe & the adjacent portion of the vermis 2. Spinocerebellum ( paleocerebellum) : this consist of intermediate zones of the 2 hemisphere & most of the vermis of the anterior & posterior lobes
Functional Divisions of the Cerebellum Spinocerebellum (Coordination of rapid muscular activities) Corticocerebellum (Planning and programming of movement) (Posteroinferior view of the cerebellum) (Vestibulocerebellum) 1. Equiilibrium 2. Coordination of postural mechanisms
Efferent (output) pathway from the CB There are 3 major efferent pathways from the 3 parts of the CB that are axons of the 3 deep nuclei that leave the CB through the superior & inferior CPs only (A) From the vestibulocerebelum : fibers from this part relay at the fastigial nucleus, from which efferent fibers arise & pass through the inferior CP to the vestibular nuclei & reticular formation (then the spinal cord via the vestibulospinal & reticulospinal tracts
Some fibers pass directly from the flocculonodular to the vestibular nuclei, so these nuclei function as Cerebellar nuclei (B) From the spinocerebellum : Fibers from this part relay at the nucleus interpositus, from which efferent fibers arise & pass through the superior CP to : (a) The ventrolateral thalamic nucleus, then to the motor cortical areas
Con (C ) from the cerebrocerebellum : Fibers from this part relay at the dentate nucleus From which efferent fibers arise & pass through the superior CP to the ventrolateral thalamic nucleus, then to the cortical motor areas (cerebello-dentato-thalamo- cortical pathway)
Main Connections of the Vestibulocerebellum Vestibular Organ VESTIBULAR NUCLEUS Floculonodular Lobe Vermis vestibulospinal tract MLF FASTIGIAL NUCLEUS lower motor neuron LMN ARCHICEREBELLUM
Main Connections of the Neocerebellum CEREBRAL CORTEX THALAMUS DENTATE NUCLEUS pyramidal tract Pontine Nucleus POSTERIOR LOBE CEREBELLAR HEMISPHERE lower motor neuron LMN NEOCEREBELLUM
1. Equilibrium Functions of the Cerebellum Flocculonodular Lobe Labyrinth Vestibular nuclei Axial muscles Vestibulospinal tracts
2. Muscle Tone C. Cortex C. White matter -ve +ve +ve Purkinji cells Deep nuclei Lateral vestibular nuclei & motor neurons Damage to the cerebellar cortex Hypertonia Damage to the cerebellar cortex and deep nuclei Hypotonia
3. Coordination of Voluntary movement
3. Coordination of Voluntary movement 1. Motor cortex informs the cerebellum about intended motor plan through cortico-ponto-cerebellar fibres. 2. A copy of the motor signals arriving at the anterior horn cells are transmitted to the cerebellum by the ventral spinocerebellar tracts 3. Proprioceptors inform the cerebellum about the performance of the muscles through dorsal spinocerebellar tracts. 4. The cerebellum compares intention of the motor cortex with performance of the muscles and corrects error in the rate, range, force and direction of movement through cerebello-thalamo-cortical fibres.
4. Coordination of involuntary movement 5. Execution of rapid ballistic movement 6. Planning and programming of movement
Cerebellar dysfunction 1. Disturbance in posture and gait a. Head is tilted to the side of the lesion b. Truncal ataxia (walk with wide base in a drunken fashion) 2. Failure of progression of voluntary movement a. Dysdiadochokinesia (inability to perform rapid successive alternating movements) b. Dysartheria (defective speech)
3. Incoordination of movement a. dysmetria: (inability to judge ahead of time the range of movement) dysmeteria results in ataxia (incoordination of movement) b. Intention tremors (course, rhythmic involuntary movements which occur during voluntary movement and disappear at rest) c. Nystagmus (tremors of the eye ball) d. Rebound phenomenon e. Decomposition of movement 4. Hypotonia, hyporeflexia, pendular jerks