ANATOMY• Latin for ‘little brain’• Largest part of hindbrain• Occupies most of posteriorcranial fossa• Lies behind pons & medulla– forming roof of 4th ventricle• Separated from posterior part ofcerebrum– by tentorium cerebelli
Diagram depicting the anatomical position of cerebellum
Connection with the brainstem Superior Cerebellar Peduncle(brachium conjunctivum)• Connects with midbrain Middle Cerebellar Peduncle(brachium pontis)• Connects with pons Inferior Cerebellar Peduncle(restiform body)• Connects with medulla
External features Two cerebellar hemispheres . Median vermis. Two surfaces ----superior andinferior 3 fissures:• fissura prima,• horizontal fissure and• posterolateral fissure 3 lobes in each hemisphere• anterior ,• posterior and• flocculonodular.
Flattened view of the cerebellar cortex showing the main cerebellar lobes, lobules, and fissures. B:Relationship between the diagram in (A) and the cerebellum.(courtesy- snell’s clinical neuroanatomy)
Internal structure Outer gray matter called cerebralcortex, extensivly folded forming folia Inner white matter, showing distinctive treelikepattern called Arbor vitae (tree of life) 4 pairs of nuclei within white matter ,the deepcerebral nuclei
The cerebral cortex Microscopically composed ofthree layers:• Outer molecular• Middle ,Purkinje cell layer and• Inner , Granule cell layer Contains five types of neurons:• Basket cell• Stellate cells• Pukinje cell – Purkinje cell layer• Granule cell &• Golgi cell Purkinje cell axons, are the onlyoutput from the cerebellar cortex,to the deep nucleiMolecular layerGranule cell layer
Inputs:• Climbing fiber(“+”, excitatory, from inferior olivenucleus)• Mossy fiber (+, excitatory,fromspinal cord & brain stem)Output:• Purkinje cell axon (“-”, inhibitory)Input and output of the cerebral cortex
The Afferent Cerebellar PathwaysAfferent Tracts Transmits DestinationDorsal spinocerebellar Unconscious kinesthetic &cutaneous afferents from trunk &legAnterior lobe,pyramis,uvula ¶median lobe via ipsilateralinferior cerebral peduncleVentral Spinocerebellar Exteroceptive and proprioceptivefibres from bodyVermis and anterior lobe viaipsilateral superior cerebralpeduncleVestibulocerebellar tract Vestibular impulse from labyrinthdirect and via vestibular nucleiFlocculonodular lobe via ipsilateralinferior cerebral peduncleCuneocerebellar tract Proprioceptive impulses, especiallyfrom arm,head and neckanterior lobe via ipsilateral inferiorcerebral peduncleTectocerebellar Auditory and visual impulses viainferior and superior colliculiLobulus simplex ,declive & tubervia superior cerebral peduncleCorticopontocerebellar Impulses from motor and otherparts of cerebral cortex via pontinenucleiAll parts of cerebellar cortexexcept flocculonodular lobe viacontralateral middle cerebellarpeduncleOlivocerebellar Proprioceptive input from wholebody via relay in inferior oliveAll parts of cerebellar cortex viacontralateral inferior cerebralpeduncle
Neural circuitry of cerebellar cortexNegativefeedbackloopFeedforwardinhibitionthe cerebellar circuitry seems to beconcerned solely with modulating ortiming the excitatory output of thedeep cerebellar nuclei
The Efferent Cerebellar Pathways The entire output of the cerebellar cortex is through the axons ofthe Purkinje cells. The axons of the Purkinje cells end by synapsing on the neurons ofthe deep cerebellar nuclei. The axons of the neurons that form the cerebellar nuclei constitutethe efferent outflow from the cerebellum. A few Purkinje cell axons pass directly out of the cerebellum to thelateral vestibular nucleus. The efferent fibers from the cerebellum connect with the rednucleus, thalamus, vestibular complex, and reticular formation
The Efferent Cerebellar PathwaysPathway Origin DestinationGlobose-emboliform-rubral Globose andemboliform nucleiTo contralateral red nucleus, then viacrossed rubrospinal tract toipsilateral motor neurons in spinalcordDentothalamic Dentate nucleus To contralateral ventrolateral nucleusof thalamus, then to contralateralmotor cerebral cortex; corticospinaltract crosses midline and controlsipsilateral motor neurons in spinalcordFastigial vestibular Fastigial nucleus Mainly to ipsilateral and tocontralateral lateral vestibular nuclei;vestibulospinal tract to ipsilateralmotor neurons in spinal cordFastigial reticular Fastigial nucleus To neurons of reticular formation;reticulospinal tract to ipsilateralmotor neurons to spinal cord
(1) CONTROL OF TONE & POSTURE:Spino-cerebellumSup. & Inf.ColliculiVesti. Nu.R.F.124567o Mainly function of Spinocerebellum.CHANGE IN BODY POSTUREProprioceptive from Body2.Cuneo-cerebellar1.Spino-cerebellar (dor. & Vent.)REFLEX CORRECTION OF MUSCLE TONEEASY MAINTANENCE OF NEW POSTURE3.Tecto-cerebellar (Visual & Auditory)4.Cereb.-vestibular5.Cereb.-reticular6.Vestibulo-spinal7.Reticulo-spinalA.H.C.Functions of the cerebellum
(2) CONTROL OF EQUILIBRIUM:o Mainly function of Vestibulocerebellum.Vestibulo-cerebellumVestibularApparatusV. N.1123CHANGE IN HEAD POSITION /ACCELARATIONLabyrinthine Afferents1.Vestibulo-cerebellarREFLEX CORRECTION OF MUSCLE TONEA.H.C.MAINTANENCE OF BODY EQUILIBRIUM2.Cereb.-vestibular 3.Vestibulo-spinalFunction of the cerebellum
Functions of the cerebellum(3) CONTROL OF VOLUNTARY MOVEMENT: Act as a “comparator of a servo mechanism” Cerebellum receives two types of information• intended plan of movement (direct information from the motorcortex)• what actual movements result (feedback from periphery) These two are compared: an error is calculated Corrective output signals goes to• motor cortex via thalamus• brain stem nuclei and then down to the anterior horn cell throughextrapyramidal tracts
Functions of the cerebellumCorrective Signals through Dentato-Thalamo-Cortical FibresCortico-Ponto-Cerebellar fibresSpino-Cerebellar Fibre.
Functions of the cerebellum(4) LEARNING NEW SKILLED VOLUNTARY MOVEMENTS: Role of Inferior Olivery Nuclei – Climbing Fibers. Each Purkinje cell receives input from a single climbingfiber Each climbing fiber cause a burst of spikes in Purkinje cell(called a “complex spike”) when new skilled movement isdone Complex spike causes long term modification of the patternof mossy fibre input to Purkinje’s cell. Climbing fibre input gets increased when new skilledmovement is learnedNormal spike Complex spike
Cerebellar dysfunctionCharacteristics feature Disturbance of posture• Hypotonia• Face rotated towards opposite side• Body weight thrown on healthy leg,concavity of trunk towardsaffected side• nystagmus Ataxia• Incoordination of movements• Decomposition of movements (movement occuring in stages)• Dysmetria- movement is poorly carried out in direction,range,and force ;past pointing (hypermetria) or falling short(hypometria) occurs
Cerebellar dysfunction Intention tremors:• Jerky movements with o and fro motion on reachingan object• Coarse tremor occuring at 4-6/sec. Slow and lalling speech. Drunken gait
Clinical test to assess cerebellar dysfunction Finger nose test Rebound Phenomenon of Holmes Adiadochokinesia- unable to carry out rapidlyalternate and opposite movements Heel-Knee test-
The planned expansion of the Haram.Thank you for the patience……………..