Cerebellum Lecture PDF

CEREBELLUM Dr. Hussni Alghuriri OBJECTIVE OF LECTURE 1. Identify the major lobes and regions of cerebellum. 2. Summarize the structure of the cerebellar cortex; identify the deep cerebellar nuclei and their connections. 3. Summarize the afferent and efferent connections of the cere...

CEREBELLUM Dr. Hussni Alghuriri OBJECTIVE OF LECTURE 1. Identify the major lobes and regions of cerebellum. 2. Summarize the structure of the cerebellar cortex; identify the deep cerebellar nuclei and their connections. 3. Summarize the afferent and efferent connections of the cerebellum and their arrangement in cerebellar peduncles. 4. Describe the major functions of the cerebellum and how each side of the cerebellum controls the ipsilateral side of the body. 5. Explain the effects of lesions of cerebellum and motor disorder associated with cerbellar lesions 1- SITE OF CEREBELLUM Situated in the posterior cranial fossa and is covered superiorly by the tentorium cerebelli that whitch seperated from occiptal lobe. It is the largest part of the hindbrain (10% of total weight) and lies posterior to the fourth ventricle, the pons, and the medulla oblongata It lies behind Pons & M.O. , separated from them by the cavity of 4 th ventricle. It is connected to brain stem (medulla, pons& midbrain) by inferior, middle & superior cerebellar pedunclesrespectively. FUNCTION OF CEREBELLUM  It controls equilibrium, it influences posture & muscle tone and coordinates the movements  Its surface is high convoluted, forming folds or folia, being oriented transversely SURFACE 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 fissure lies along the sides of cerebellum, extending from anterior notch to posterior notch, separates the superior from the inferior surfaces. 3- Secondary (posterolateral) fissure lies on inferior surface and separates flocculo-nodular lobe from the ramainder of cerebellum SURFACE OF CEREBELLUM Inferior surface : rounded on each side and presents : a deep groove (vallecula) between the 2-cerebellar hemispheres,which is occupied by the inferior vermis. -Tonsil is a small part of cerebellar hemisphere that lies lateral to inferior vermis. NOTCHES OF CEREBELLUM anterior notch 1- wider and 2-lodging the back of pons & medulla. 3- It is separated from them by cavity of 4 thventricle posterior notch - occupied by falx cerebelli, which separates the 2 cerebellar H. HEMISPHERE OF CEREBELLUM The cerebellum consists of a midline vermis and 2-lateral hemispheres.  Cerebellar Peduncles Three paired fiber tracts connect the cerebellum to the brainstem: ♦ Superior peduncles connect the cerebellum to the midbrain; ♦ Middle peduncles connect the cerebellum to the pons and to the axis of the brainstem; ♦ Inferior peduncles connect the cerebellum to the medulla. Cerebellar Peduncles  Cerebellar Peduncles Superior peduncles (to the midbrain): Fibers originate from neurons in the deep cerebellar nuclei & communicates with the motor cortex via the midbrain and the diencephalon (thalamus) Middle peduncles (to the pons): Cerebellum receives information advising it of voluntary motor activities initiated by motor cortex Inferior peduncles (to the medulla): Afferents conveying sensory information from muscle proprioceptors throughout the body & from the vestibular nuclei of the brainstem (Spinal cord) LOBES OF CEREBELLUM Anatomically , it is divided into anterior , posterior & flocculo-nodular lobes. ANATOMICAL SUBDIVISION 1. Anterior lobe: in front of primary fissure, on the superior surface. 2. Posterior (middle) lobe: behind primary fissure (Between Primary & Secondary/posterolateral fissures). 3. Flocculonodular lobe: in front of secondary (Posterolateral) fissure, on the inferior surface. FUNCTIONAL SUBDIVISION OF CEREBELLUM : 1- Archi-cerebellum = posterior lobe (Vestibular part) : _ It is formed of the flocculo-nodular 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 vestibular apparatus of internal ear Via vestibulo- cerebellar tracts. _It is concerned with equlibrium Schematic drawing of cerebellum showing the relationships between the anatomical & functional divisions of cerebellum. Green =archi-cerebellum, blue=paleo-cerebellum.  Pink= neo-cerebellum I- ARCHICEREBELLUM  It is concerned with equilibrium.  It represents flocculo-nodular lobe.  It has connections with vestibular & reticular nuclei of brain stem through the inferior cerebellar peduncle.  Afferent vestibular Fs. Pass from vestibular nuclei in pons & medulla to the cortex of ipsilateral flocculo-nodular lobe.  Efferent cortical (purkinje cell) Fs. Project to fastigial nucleus, which projects to vestibular nuclei & reticular formation.  It affects the L.M.system bilaterally via descending vestibulo-spinal & reticulo-spinal tracts. 2- PALEO-CEREBELLUM= (SPINAL PART) : it is formed 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 of midbrain. -it is concerned with muscle tone 2-PALEO-CEREBELLUM  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.  Efferents cortical fibres pass to globose & emboliform nuclei, then Via sup. C. peduncle to contra-lateral red nucleus of midbrain to give rise descending rubro-spinal tract. 3- NEO-CEREBELLUM= (CEREBRAL PART) : It is the 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- ponto- cerebellar pathway. -it sends efferents to ventro latral nucleus of thalamus. -it controls voluntary movements (muscle coordination ) 3- NEO-CEREBELLUM= (CEREBRAL PART) :  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).  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 & cortico-bulbar pathways.  Efferents of dentate nucleus form a major part of superior C. peduncle  Archicerebellum Paleocerebellum Neocerebellum Nuclei Fastigial Globose & Emboliform Dentate Related Afferents from Vestibular nuclei from spinal cord from Pons (Vestibulocerebellar fibres), (dorsal spinocerebellar (Pontocerebellar fibres) (through ICP) tracts through ICP & (through MCP) ventral spinocerebellar tract through SCP) Efferents cortical (purkinje cell) Fibres to globose & embliform to Red nucleus but mostly project : to Fastigial nucleus, nuclei which project to to which projects to vestibular red nucleus Ventral Lateral Nucleus nuclei (through ICP) + to (through SCP) of Reticular formation Thalamus (through SCP) then to motor cortex Function 1. controls body Balance controls posture & coordination of voluntary (via vestibulospinal & muscle tone movements reticulospinal tracts). (via Rubrospinal tract). (via descending 2. Control of eye movement corticospinal (via VO vestibulo-ocular reflex) & corticobulbar tracts or rubrospinal tract).  Archicerebellum Paleocerebellum Neocerebellum Content Floculonodular lobe Ante.lobe except Posterior lobe except and lingula lingula Pyramid and uvula Pyramid and uvula of poste lobe Connection With vestibular nuclei Spinal cord Cerebral cortex INTERNAL STRUCTURE OF CEREBELLUM : It consists of an outer layer of grey matter (cerebellar cortex) , & inner layer of white matter containing 4-pairs of cerebellar nuclei : above roof of 4th V. from medial to lateral : 1-Fastigial nucleus. 2-Globose nucleus. 3-Emboliform nucleus. 4-Dendate nucleus. (the only one that can be seen clearly with the naked eye). CEREBELLAR CORTEX  It is highly convoluted, forming numerous transversely oriented folia.  It contains nerve cells, dendrites and synaptic connections of cellular neurones.  The cellular organization of the cortex consists of 3-layers :  1-Outer molecular layer.  2-Intermediate, purkinje cell layer.  3-Inner granular layer, which is dominated by granule  CEREBELLAR CORTEX  Molecular layer : contains  1-Cells : molecular cells (stellate cells) & basket cells. 2-Nerve Fibres : a- dendrites 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 folium.  Granular layer : it is formed of small granule cells & ending of mossy fibres.  There are 3-types of Nerve Fibres in white Matter : 1-Axons 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 molecular layer. AFFERENT FIBRES TO CEREBELLUM : Mostly end in cerebellar cortex, excitatory to cortical neurones as mossy or climbing Fs. passing through the cerebellar peduncles. The following are Afferent fibres: 1-dorsal & ventral spino-cerebellar tract. (passing via I.C.P & S.C.P) 2-vestibulo-cerebellar Fs. (via I.C.P) 3-olivo-cerebellar Fs. (via I.C.P)/ (extrapyramidal fibres), (end as climbing or mossy fibres) 4-ponto-cerebellar Fs. (via M.C.P). EFFERENT FIBRES OF THE CEREBELLUM : It sends the following fibres : 1-Cerebello-vestibular Fs. to vestibular nuclei of pons & M.O. 2-Cerebello-olivary Fs. To M.O. 3-Dendato-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 cortico-spinal & corticobulbar tracts. BLOOD SUPPLY Posterior inferior cerebellar artery Anterior inferior cerebellar artery  Branch of basilar artery Superior cerebellar artery  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 Chacot’triad, which is highly diagnostic of the disease.  CEREBELLAR INPUTS Vermis  Receives input from spinal cord regarding somatosensory and kinesthetic information (intrinsic knowledge of the position of the limbs)  Damage leads to difficulty with postural adjustments (cerebellar ataxia) Intermediate Zone  Receives input from the red nucleus and somatosensory information from the spinal cord  Damage results in rigidity & difficulty in moving limbs Lateral Zone  Receives input from the motor and association cortices through the pons  Projects to the dentate nucleus, which projects back to primary and premotor cortex  Damage leads to 4 types of deficits: - Ballistic movements (cerebellar ataxia) - Coordination of multi-joint movement (lack of coordination: asynergia) - Muscle learning (loss of muscle tone: hypotonia) - Movement timing Clinical Findings and Localization of Cerebellar Lesions Ataxia refers to disordered contractions of agonist and antagonist muscles and lack of coordination between movements at different joints typically seen in patients with cerebellar lesions. Normal movements require coordination of agonist and antagonist muscles at different joints in order for movement to have smooth trajectory. In ataxia movements have irregular, wavering course consisting of continuous overshooting, overcorrecting and then overshooting again around the intended trajectory. Dysmetria = abnormal undershoot or overshoot during movements toward a target (finger-nose-finger test). 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. 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 laterally to form a lateral recess on each side to open into subarachnoid space. 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 4TH VENTRICLE -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. -Inf.medullary velum connects the 2 inf.cerebellar peduncles. -Inferior vermis of cerebellum : lies in the middle of roof of 4th ventricle. THE ROOF OF 4TH VENTRICLE The lower part of roof is 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 TH VENTRICLE The roof contains 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 cerebello-medullary angle 2 lateral openings (foramina of Luschka) : each one lies at the lateral end of lateral recess to open into subarachnoid space at cerebello-pontine angle. choroid plexus partly protrudes out through each lateral aperture. 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) & lower (medullary) part. A diagram to show the floor & 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 nucleus. 3-Superior fovea : a groove lateral to facial colliculus. 4-Vestibular area : lateral to superior fovea. It overlies superior, medial & A diagram to show the floor & lateral lateral vestibular nuclei. boundaries of 4th ventricle. THE FLOOR OF 4TH VENTRICLE Lower medullary part : presents on each side of the median sulcus. 1-Inferior fovea : inverted V- shaped groove. 2-Hypoglossal area : medial to inferior fovea. It overlies hypo-glossal nucleus. 3-Vagal area (triangle) : between limbs of inferior fovea.It overlies dorsal nucleus of vagus. 4-Vestibular area : lateral to inferior fovea. It overlies inferior vestibular nucleus. A diagram to show the floor & lateral boundaries of 4th ventricle.