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Some images on cerebellum:

Location of cerebellum:

  • Largest part of hindbrain
  • Occupies most of posterior cranial fossa
  • Lies behind pons & medulla
    • forming roof of 4th ventricle
  • Separated from posterior part of cerebrum
    • by tentorium cerebelli

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Cerebral peduncles:

Joined to the brain stem via:

  • Superior cerebellar peduncle –> Midbrain
  • Middle cerebellar peduncle –> Pons
  • Inferior cerebellar peduncle –> Medulla

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Fibres in peduncles:

  • Superior peduncle
    • ventral spino-cerebellar
      • only spinocerebellar tracts go thru sup peduncle
    • cerebello-thalamic
    • cerebello-rubral (red nucleus)
  • Middle peduncle
    • ponto-cerebellar
  • Inferior peduncle
    • vestibulo-cerebellar
      • vesticular nuclei
    • posterior spino-cerebellar
      • lower limb
    • cuneo-cerebellar
      • upper limb
    • reticulo-cerebellar
      • reticular nuclei
    • olivo-cerebellar
      • olive nuclei

 

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Gross Anatomy

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  • Shape: Ovoid
  • 2 cerebellar hemispheres
    • united by a constricted median part
      • Vermis (spine of cerebellum)
        • Superior vermis
        • Inferior vermis
  • Inferior aspect
    • 2 halves are separated by a hollow: VALLECULA
  • Hemispheres show parallel fissures
    • separating thin rounded FOLIA
    • similar to cerebral sulci/gyri

Lobes & Fissures

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  • Hemispheres divided into
    • 3 lobes
      • Middle lobe: largest part
    • 2 fissures
      • Primary Fissure
        • V-shaped with apex directed backwards
        • Separates anterior lobe from middle lobe
      • Horizontal fissure
        • deep along posterior margin
        • separates superior & inferior surface
        • no functional significance
  • Posterolateral fissure
    • separates middle lobe from floncculonodular lobe
    • Flocculonodular lobe (hidden in the inferior part)
      • laterally placed small ovoid flocculus connected medially to nodule (on inferior vermis)

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  • Neocerebellum: helps cerebral cortex in timing & program complex activities

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Phylogenetic & Functional Parts

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  • Flocculonodular lobe
    • smallest
    • constitute phylogenetic archicerebellum
      • functional vestibulo-cerebellum
      • primitive, old
        • still reacting to stimuli from balance organ vestibule & 8th nerve
  • Anterior lobe
    • antero-superior part
    • includes most of superior vermis & anterior-most part of superior surface
    • Anterior lobe + (Pyramid + Uvula of vermia)
      • constitutes phylogenetic paleocerebellum
        • functional spino-cerebellum
      • reacting to simuli from proprioceptive endings in muscles and tendons
        • spino-cerebellar tracts, reticulo-cerebellar tracts
  • Middle lobe (also known as posterior lobe)
    • a large part of cerebellar hemisphere
      • entire inferior surface & most of superior surface
    • behind primary fissure
    • constitute phylogenetic neocerebellum
      • functional cerebro-cerebellum
      • reacting to stimuli from opposite cerebral cortex about planned movements
      • eg. right cerebral cortex control kicking of left leg.
        • if not developed properly, difficulty in kicking left leg. vice versa

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Functional Anatomy & Afferent, Efferent Connections of Cerebellum

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Vestibulocerebellum (Flocculonodular lobe)

  • responds to vestibular stimuli from internal ear
    • assists in maintaining equilibrium by modification in muscle tone
    • postural muscles
      • eye muscles
      • trapezius
      • sternomastoid
      • erector spinae
  • Main deciding factor: fastigial nucleus
    • which deep nucleus controls equilibrium: fastigial nucles
  • Afferent:-
    • Vestibulo-cerebellar
      • via inferior cerebellar peduncle
      • from vestibular nuclei in the floor of 4th ventricle
      • also from vestibular nerve (8th nerve)
  • Efferent:-
    • Cerebello-vestibular
      • via inferior cerebellar peduncle
      • mainly to lateral vesticular nucleus
    • Cerebello-reticular
      • reticular nucleus brain stem
    • ——> then via vestibulo-spinal & reticulo-spinal tract modify the lower motor neurons

image

Spinocerebellum (Anterior lobe)
Paleocerebellum

  • Responds to
    • proprioception input from muscle spindle
    • touch/pressure input
  • Maintains posture of the body by
    • modifying muscle tone
    • regulate voluntary movements
  • Afferent:-
    • from spinal cord
    • from lower limb, trunk
      • via posterior spino-cerebellar tract
    • from upper limb, thorax
      • via anterior spino-cerebellar tract
      • via cuneo-cerebellar tract
  • Efferent:-
    • cerebello-cerebral
      • via thalamus
    • cerebello-reticular
    • cerebello-rubral
      • to red nucleus in midbrain
    • ——–> then via reticulo-spinal & rubro-spinal tract modify the gamma motor neurons in spinal cord
      • modify muscle tone

image

Neocerebellum

  • receives input from cerebral cortex & olivary nucleus
    • facilitates smooth coordinated voluntary movements
    • ensures that the force, direction & extent are accurate
    • role in motor learning (learn diff movements)
      • athletes
      • timing & amplitude of learned movements are encoded here
    • diverse cognitive functions
      • attention
      • processing of language
  • any smooth movements require perfect synergism between agonist & antagonist group of muscles
  • Afferent:-
    • Cortico-ponto-cerebellar
      • via middle cerebellar peduncle
      • from motor areas of opposite cerebral cortex after synapse in pontine nuclei
      • there fibres – anatomical basis of control of cerebellar activity by cerebral cortex
    • Olivo-cerebellar
      • via inferior cerebellar peduncle
      • from inferior olivary nucleus in medulla
  • Efferent:-
    • Cerebello-thalamic
      • via superior cerebellar peduncle
      • the to motor cortex
        • via cortico-spinal tract & cortico-nuclear fibres
        • coordinate voluntary movements
    • Cerebello-rubral
      • via superior peduncle
      • to red nucleus

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Histology

image

  • Similar to cerebral cortex
    • central white matter
    • peripheral grey matter
  • Midsagittal section
    • multiple folia containing core of white matter covered superficially by grey matter
  • Central core of white matter contains
    • 4 intra-cerebellar nuclei
      • receiving input from cerebellar cortex
      • extending outflow (axons) via superior & inferior peduncles

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MEDIAL TO LATERAL

  • Fastigial nuclei (medial)
    • primitive
    • receives input from vermis (archicerebellum)
  • Globose, emboliform nuclei
    • together known as interpositus
    • receive input from paravermal area (spinocerebellum)
  • Dentate nuclei (lateral)
    • receives input from most of cerebellar hemisphere (neocerebellum)
    • largest nucleus

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Microscopic structure of cerebellar cortex (3 layers)

  • External Molecular layer
  • Middle Purkinje layer
    • large flask shaped neurons
    • arranged in single tier
      • in a plane transverse to folium
    • dendrites produce profuse branching
    • receive communications afferent fibres entering cerebellum
    • axons run to DEEP CEREBELLAR NUCLEI
      • sole output of cerebellar cortex
    • functionally
      • inh
        ibitory (GABA)

        • stimulated purkinje inhibits deep nuclei
  • Internal Granular layer
    • closely packed small neurons

image

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All afferent input via 2 different fibres:

  • Mossy fibre
    • entire inflow of cerebellum
      • except from inferior olive
      • particularly from cerebral cortex via pons
    • they synapse in expanded MOSS-like appearance with granule & golgi cells in granular layer
    • fast-firing
      • rapid adjustment for ongoing movement
  • Climbing fibre
    • inflow from inferior olive
    • run up and synapse with dendrites of single Purkinje cell
    • slow-firing
      • helps in learning muscle habits

Circuitry of Cerebellum

image

Process:

  • Afferent
    • equilibrium, vestibule, 8th nerve
    • proprioception, touch, pressure
    • planned voluntary movement, opposite cerebral cortex
  • enter via 3 peduncles
  • all afferents reach cerebellar cortex through 2 types of fibres
    • mossy fibre
    • climbing fibre
  • stimulate purkinje cells
    • axons inhibit cerebellar nuclei
  • leave cerebellum via superior peduncle & inferior peduncle

Influence motor activity, indirectly via:

  • vestibular nuclei
  • corpus nuclei
  • red nucleus
  • reticular formation
  • cerebral cortex

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Blood supply

  • Superior surface
    • Superior cerebellar branch of basilar artery
  • Inferior surface (Anterior part)
    • Anterior inferior cerebellar branch of basilar artery
  • Inferior surface (Posterior part)
    • Posterior inferior cerebellar branch of verterbral artery

Veins

  • Straight sinus
  • Occipital sinus
  • Transverse sinus

*Trombosis will affect many organs – because brainstem controls many important activities of the body

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Vestibulo-Cochlear apparatus

  • Lateral line of organ of fish and amphibian
  • enable fish to keep upright

Human vestibular apparatus

  • vestibule, vestibular nerve, vestibular nucleus, cerebellum, vestibulospinal tract, superior colliculus, medial longitudinal fasciculus, tectospinal tract, reticulospinal tract
    • responsible for maintanence of equilibrium
    • based on perceived movements of the head
  • Reflex adjustments
    • muscle tone
    • muscle tension
    • muscle contraction
  • Muscles involved
    • neck muscles
      • movement of head
    • muscle of spine
      • resist pull of gravity
    • extraocular muscle
      • maintain movement of eyes with head position

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Vestibular disorders

Disturbance of vestibular function:

  • Central
    • brain stem vestibular nuclei affected
  • Peripheral
    • labyrinth (internal ear)
    • vestibular component of 8th nerve

Giddiness (Vertigo)

  • Nystagmus (check vestibular function)
    • disturbance of reflex control of extraocular muscles
      • vestibulo-ocular reflex
      • involuntary to-and-fro movement (rhythmic) of the eyes
    • Types:
      • Vestibular nystagmus
        • uncontrollable rhythmic oscillation of the eyes
        • fast phase is away from the side of lesion
        • central lesion: spontaneous nystagmus without a cognitive, visual or vestibular stimulus
          • see nystagmus even without stimulus
      • Cerebellar nystagmus
        • disorder of cerebellum by tumour, thrombosis, ischaemia, trauma)
        • unilateral lesion
          • amplitube greater when eyes rotated to the side of lesion
          • can be horizontal/vertical
  • Ataxia
    • incoordination / clumsiness of movements

Signs of cerebellar disorder

  • Always ipsilateral (same sided)
  • No paralysis
  • No sensory loss
  • Wide-based gait
    • on walking, staggers to the affected side
  • Hypotonia
    • shaking limb, excessive movement of terminal joints
  • Ataxia
    • disturbance of coordinated voluntary movement
    • tremor on fine movements
      • writing
      • shaving
      • buttoning
  • Finger-nose test
    • past-pointing to ear instead
  • Heel-knee test
    • unable to do properly
  • Pendular knee reflex
    • continue longer
  • Dysdiadochokineses
    • on pronation & suppination of forearm rapidly
    • imcomplete & jerky movement
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Terri is obsessed with making medical school as painless as possible. She studies and compiles medical school notes in a concise, easy-to-understand format. She also enjoys reading contributions by others. She is an investor in sustainability projects. Her ideal weekend is wine tasting and experimenting on bread-making. She has yet to master the art of Sourdough baking.

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