Cerebellar structure, function and vestibular disorder

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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

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

• 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

• 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)

 

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

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Phylogenetic & Functional Parts

• 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

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

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

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

• 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

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

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

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

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