Cerebellum - shahed.ac.ir

Cerebellum - shahed.ac.ir

General Features of Cerebellum The: cerebellum consists of a midline vermis and 2-lateral hemispheres. Anatomically , it is divided into , posterior & anterior It controls equilibrium, it flocculo-nodular influences posturelobes. & muscle tone and coordinates the movements Lateral aspect of

brain stem & cerebellum , showing cerebellar peduncles. Its surface is high convoluted, forming folds or folia, being oriented transversely It lies behind Pons & M.O. , separated from them by the th External Features of Cerebellum : It has anterior notch ,which is wider and lodging the back of pons & medulla. It is separated from them by cavity of 4thventricle

Superior surface It has also posterior notch occupied by falx cerebelli, which separates the 2 cerebellar H. Inferior surface : rounded on each side and presents : Inferior surface a deep groove (vallecula) between the 2-cerebellar External Features of Cerebellum:Superior surface : lies beneath tentorium cerebelli and has a raised superior vermis + a

large cerebellar hemisphere on each side + primary & horizontal fissures. 1- Primary fissure V-shaped,well defined fissure, lies on superior surface and separates the small anterior lobe from the larger middle lobe (or posterior lobe). 2- Horizontal 3- Secondary (posterolateral) fissure lies along the sides of fissure lies on inferior cerebellum, extending from surface and separates flocculoanterior notch to posterior notch, nodular lobe from the ramainder separates the superior from the Functional

subdivision of 1Archi-cerebellum = cerebellum : posterior lobe (Vestibular part) : _ It is Schematic drawing of cerebellum showing the relationships between the anatomical & functional divisions of cerebellum. Green =archi-cerebellum, blue=paleo-cerebellum. Pink= neocerebellum formed of the flocculonodular lobe + associated

fastigial nuclei, lying on inf. Surface in front of postero-lateral fissure. _Embryologically, it is the oldest part of cerebellum. _It receives afferent Fs. From I- Archicerebellum It is concerned with equilibrium. It represents flocculonodular lobe. It has connections with vestibular & reticular nuclei of brain stem through the inferior cerebellar peduncle. Afferent vestibular Fs. Pass

Connections of archicerebellum from vestibular nuclei in pons & medulla to the cortex of ipsilateral flocculo-nodular lobe. Efferent cortical (purkinje 2- Paleocerebellum= (spinal part) : -_it is formed Schematic drawing of cerebellum showing the relationships between the anatomical & functional divisions of cerebellum. Green =archi-cerebellum, blue=paleocerebellum.

Pink= neo-cerebellum of midline vermis + surrounding paravermis + globose & emboliform nuclei. _It receives afferent proprio-ceptive impulses from Ms.& tendons Via spino-cerebellar tracts (dorsal & ventral) mainly. -it sends efferents to red nucleus 2-Paleocerebellum It is concerned with muscle tone & posture.

Afferents spinal Fs. consist of dorsal & ventral spino-cerebellar tract from muscle, joint & cutaneous receptors to enter the cortex of ipsilateral vermis & para vermis Via inferior & superior cerebellar peduncles . Connections of Paleocerebellum. Efferents cortical fibres pass to globose & emboliform nuclei, then 3- Neocerebellum= (cerebral part) : _It is the

Schematic drawing of cerebellum showing the relationships between the anatomical & functional divisions of cerebellum. Green =archi-cerebellum, blue=paleo-cerebellum. Pink= neocerebellum remaining largest part of cerebellum. _It includes the most 2-cerebellar hemispheres + dendate nuclei. _It receives afferent impulses from the cerebral cortex+pons Via cerebro-pontocerebellar pathway.

3- NeocerebellumIt is concerned with muscular coordination. It receives afferents from cerebral cortex involved in planning of movement- to pontine nuclei ,cross to opposite side Via middle Cerebellar peduncle to end in lateral parts of cerebellum (cerebro-ponto-cerebellar tract). Connections of Neocerebellum. Neo-cerebellar efferents project to dendate nucleus,which in turn projects to contra-lateral red nucleus & ventral lateral nucleus of

thalamus ,then to motor cortex of frontal lobe, giving rise descending cortico-spinal & Cerebellar Lesions Are usually vascular, may be traumatic or tumour. Manifestations of unilateral cerebellar lesions : 1-ipsilateral incoordination of (U.L) arm = intention tremors : it is a terminal tremors at the end of movement as in touching nose or button the shirt.

2-Or ipsilateral cerebellar ataxia affects (L.L.) leg, causing wide-based unsteady gait. Manifestations of bilateral cerebellar lesions (caused by alcoholic intoxication, hypothyrodism, cerebellar degeneration & multiple sclerosis) : 1-dysarthria : slowness & slurring of speech. 2-Incoordination of both arms.= intention tremors. 3-Cerebellar ataxia : intermittent jerky movements or staggering , wide-based, unsteady gait. 4-Nystagmus : is a very common feature of multiple sclerosis. It is due to impairment coordination of eye movements /so, incoordination of eye movements occurs and eyes exhibit a to-and-fro motion. Combination of nystagmus+ dysarthria + intension tremors constitutes Chacottriad, which is highly diagnostic of the disease.

Internal Structure of cerebellum : It consists of an Sagittal section of cerebellum. T.S.of cerebellum & brain at level of 4th V. to show cerebellar nuclei. outer layer of grey matter (cerebellar cortex) , & inner layer of white matter containing 4pairs of cerebellar nuclei : above roof of 4th V. from medial to lateral : 1-Fastigial nucleus.

2-Globose nucleus. Cerebellar cortex It is highly convoluted, forming numerous transversely oriented folia. T.S of cerebellar folia showing layers of cerebellar cortex. Afferent & Efferent connecltions and their relationships to principal cells of cerebellar cortex. It contains nerve cells,

dendrites and synaptic connections of cellular neurones. The cellular organization of the cortex consists of 3layers : 1-Outer molecular layer. 2-Intermediate, purkinje cell layer. Cerebellar Molecular layer : cortex contains 1-Cells : molecular cells (stellate cells) & basket cells. 2-Nerve Fibres :

adendrites of Purkinje cells (arborisations). B-axons of granule cells. ( bifurcate to produce 2-parallel fibres , oriented along long axis of folium). C-ending of climbing fibers. Purkinje cell layer : it is formed of one layer (unicellular) of large flask-shaped purkinje cells. Their arborisations are at right angles to long axis to MThere are 3-types of Nerve Fibres in white Matter : 1Axons of purkinje cells : the only axons to

leave cerebellar cortex to end in deep cerebellar nuclei specially dendate nucleus. 2-Mossy Fibres : end in the granular layer. 3-Climbing Fibres : end in the Afferent Fibres to cerebellum : Mostly end in cerebellar cortex, excitatory to cortical neurones, as mossy or climbing Fs. passing through the cerebellar peduncles. (In M.O) The following are

Afferent fibres: 1dorsal & ventral spinocerebellar tract. (passing via I.C.P & S.C.P) 2-vestibulo-cerebellar Fs. Efferent Fibres of the cerebellum : M It sends the following fibres : 1-Cerebello-vestibular Fs. to vestibular nuclei of pons & M.O. 2-Cerebello-olivary Fs. To M.O. 3Dendato-rubro-thalamic tract To red nucleus of midbrain & ventro-lateral nucleus of the thalamus

and finally to motor cortex of frontal lobe to coordinate movement via The Fourth Ventricle It is a cavity of hindbrain. Position : lies between pons & M.O. anteriorly and the cerebellum posteriorly. It is a diamond-shaped space which is lined by ependyma. Its superior angle is continuous with cerebral aqueduct of midbrain. inferior angle is continuous with centeral canal of closed M.O.

Its lateral angles extend The Boundaries of 4th Ventricle Superiolateral boundary : -it is formed by superior cerebellar peduncle on each side. Inferiolateral boundary : -it is formed by inferior cerebellar peduncle + gracile & cuneate tubercles on each side. The Roof of 4 Ventricle

th -it is a tent-shaped when seen laterally, and diamond-shaped when seen behind. -it is formed of superior & inferior medullary vela, which are thin sheets of white matter /consists of : ependyma covered by pia mater. Sup.medullary velum connects the 2 sup.cerebellar peduncles. The Roof of 4 Ventricle

The lower part of roof is th invaginated by tela choroidea of 4th ventricle. The tela choroidea is a double layer of pia mater which encloses the choroid plexus of 4th ventricle. The choroid plexus is a vascular capillary tuft covered by ependymal cells and secretes C.S.F. into the lumen of 4th ventricle. The Openings of 4 Ventricle The roof contains th 3

aperatures which transmit C.S.F. from ventricular lumen to subarachnoid space. Median aperature (foramen of Magendie) : lies in the median plane at lower end of inferior medullary velum, and opens into subarachnoid space at cistrna magna at cerebellomedullary angle 2 lateral openings (foramina of Luschka) : each one lies at the lateral end of lateral recess to open into The Floor of 4th Ventricle It is called rhomboid fossa. It is diamond-shaped

and is divided into right & left halves by the median sulcus. It is crossed in the middle by transvere Fs. (ponto-cerebellar Fs.)called medullary stria, which divide floor of 4th ventricle into upper (pontine) & A diagram to show the floor & lower (medullary) lateral boundaries of 4th ventricle. The Floor of 4th Ventricle Upper pontine part : presents on each side of median sulcus.

1-Medial eminence : a rounded elevation produced by the abducent nucleus. 2-Facial colliculus : an elevation on the top of lower part of medial eminence. It is produced by the fibres of facial nerve which surround abducent A diagram to show the floor &nucleus. lateral boundaries of 4th ventricle. The Floor of 4th Ventricle Lower medullary part : presents on each side of the median sulcus. 1Inferior fovea : inverted

V-shaped groove. 2Hypoglossal area : medial to inferior fovea. It overlies hypoglossal nucleus. 3-Vagal area (triangle) : between limbs of inferior fovea.It overlies dorsal nucleus of vagus. A diagram to show the floor & 4-Vestibular area th lateral boundaries of 4 ventricle.

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