Blood Supply Structure

The cerebellum is supplied by the:

• Basilar artery
  i – Superior cerebellar a
  = supplies the superior surface of the cerebellum
  ii – Anterior inferior cerebellar a.
  = supplies the anterior & inferior parts of the cerebellum
  
• Vertebral artery
  iii – Posterior inferior cerebellar a. (tortuous arteries)
  = supplies: – inferior surface of the vermis
  – central nuclei of the cerebellum
  – undersurface of the cerebellar hemisphere

Function of Cerebellum

1. Maintenance of Equilibrium – balance, posture, eye movement
2. Coordination of half-automatic movement of walking and posture maintenance – posture, gait
3. Adjustment of Muscle Tone
4. Motor Leaning – Motor Skills
5. Cognitive Function

• Two neuro anatomical features of clinical important are:
  – Cortex of cerebellum has a uniform microscopic structure identical in all regions
  – Cerebellar hemisphere connected to same side of the body, lesion give rise to signs and symptoms in the same side of the body

APPLIED ANATOMY: VARIOUS CEREBELLAR DYSFUNCTION

The cerebellar lesions -> deficits in coordinating movements; clinical (motor) signs of cerebellar lesions are always IPSILATERAL to the lesion -> cerebellar syndrome

• Dysdiadochokinesia – jerky action; unable to make rapid alternating movement
• Ataxic gait
• Slurred speech – slow, slurred, too (loud, soft, long, short ), scanning speech
• Hypotonia
• Intentional tremor – tremor during movement
• Nystagmus – horizontal tremor/ ossilatory movement of the eyes while looking to other side
• Gait – staggering gait

Flocculonodular lobe syndrome

• Disturbance of balance
• Trunkal ataxia
• Lack of coordination of paraxial muscles
• Attempts to walk on a wide base
• In severe cases: impossible for patient to sit or stand without falling

Anterior Lobe Syndrome

• Gait ataxia
• Uncordinated, clumsy movements of the lower limb

Posterior lobe syndrome

• Loss of coordination of voluntary movements
• Intention tremor *Intention tremors are slower types of tremors, so the movements look broader and coarse

• Cerebellar lesions causes:
  1) Incoordination of the upper limbs (intention tremor)
  2) Lower limbs (Cerebellar ataxia)
  3) Speech (Dysarthria)
  4) Eyes (Nystagmus)
  – involuntary to and fro movements of the eyes, due to lack of muscle coordination

• Consist of 3 functional subdivisions:
  1) Archicerebellum
  – Flocculonodular lobe + Fastigial nuclei
  2) Paleocerebellum
  – Vermis + paravermis + Globose and Emboliform nuclei
  3) Neocerebellum
  – Cerebellar hemisphere + Dentate nuclei

Archicerebellum

1) Archicerebellum: posterior lobe (Vestibular part):

– it is formed by flocculonodular lobe +fastigial nuclei

– it receives afferent fibres from vestibular apparatus of internal ear via vestibulo-cerebellar tracts.

– Embryologically, it is the oldest part of cerebellum.

– it is concerned with equilibrium.

– connections with *vestibular & reticular nuclei ofbrain stem through the inferior cerebellar peduncle.

– *Afferent vestibular fibres pass from vestibular nuclei (in pons & medulla) to the cortex of ipsilateral flocculonodular lobe.

– *Efferent cortical (Purkinje cell) fibres project to fastigial nucleus, which projects to vestibular nuclei & reticular formation.

– It affects the lower motor system bilaterally via descending vestibulospinal & reticulospinal tracts.

Paleocerebellum

2) Paleocerebellum:
– It is formed by midline vermis + surrounding paravermis + globose & emboliform nuclei.

– It receives afferent proprio-ceptive impulses from muscles & tendons (*Spinocerebellar tract).

– It is concerned with muscle tone & posture.

– Afferents spinal fibres consist of dorsal & ventral spinocerebellar 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 superior cerebellar peduncle to contra-lateral *red nucleus of midbrain to give rise descending rubro-spinal tract.

Neocerebellum

3) Neocerebellum:
– it is the remaining largest part of cerebellum.

– it includes the most 2-cerebellar hemispheres + dentate nuclei.

– 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).

-it sends *efferents to ventro-lateral nucleus of thalamus.

– it controls voluntary movements (muscle coordination).

– Neocerebellar efferents project to dentate 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 cerebellar peduncle.

Afferent Fibres

Afferent fibers to cerebellum:

• Arise from:
  1) Spinal cord (Spinocerebellar fibers)
  2) Inferior Olivary nucleus (Olivocerebellar fibers
  3) Vestibular nuclei (Vestibulocerebellar fibers)
  4) Pons (Pontocerebellar fibers)
• Enter through one of the peduncles, and go to cortex
• Terminate in the cerebellar cortex where they are excitatory to cortical neurons

* Fibers from inferior olivary nucleus end asclimbing fibers, others end as mossy fibers.

Cerebellar AFFERENT pathway

• From cerebral cortex
  -cortico-ponto-cerebellar fibres
  – cerebro-olivo-cerebellar fibres
  – cerebro- reticulo-cerebellar fibres
• From spinal cord
  – anterior spinocerebellar tract
  – posterior spinocerebellar tract
  – cuneocerebellar tract
• From vestibular nucleus – vestibulocerebellar tract [ flocculonodular lobe ]
• From other areas
  – red nuclelus, tectum

Climbing fibres & Mossy fibres:

• climbing fibres go directly to the Purkinje cell.
• mossy fibres DO NOT go directly to the Purkinje cell.
• Each mossy fibre branches profusely in the white matter. Each of these branches has multiple (up to 50) swellings (that resembled moss to the old time neuroanatomists)

Efferent Fibres

• The axons of the Purkinje cells are the ONLY axons to leave the cerebellar cortex
• Most of the fibres end in the cerebellar nuclei 4 cerebellar nuclei:
  1) Fastigial nucleus
  2) Globose nucleus
  3) Emboliform nucleus
  4) Dentate nucleus
  – largest

Efferent fibres of the cerebellar nuclei:

• Efferent fibres end in :
  1) Vestibular nuclei of the medulla & pons
  2) Reticular nuclei of the medulla & pons
  3) Red nucleus of the midbrain
  4) Ventral lateral nucleus of the thalamus

Cerebellar Cortex

• Consist of:
  – outer layer of grey matter = cerebellar cortex
  – inner core of white matter afferent & efferent fibers
• 4 pairs of cerebellar nuclei

Cerebellar cortex:

• Cell bodies, dendrites, and synaptic connections of cerebellar neurons
• 3 layers:
  – Outer = Molecular layer
  – Intermediate = Purkinje cell layer
  – Inner = Granular layer

Purkinje Cell

• Purkinje cells:
  – largest in CNS
  – Receive 200,000 synapses
  – Inhibitoryonly cerebellar cortex
  – neurons sending axons to cerebellar nuclei

• Cortex has 1012 neurons; more than cerebral cortex

External Structure

• Situated in the posterior cranial fossa
• Covered superiorly by the tentorium cerebelli = fold of dura mater
• Lies post. to the pons, medulla oblongata & 4th ventricle
• Consists of 2 cerebellar hemispheres joined by a narrow median verm
• 2 surfaces, superior & inferior is
• Surface of the cerebellum is marked by a series of fissures
• Cortex folded in ridges called folia; white matter resembles a tree (arbor vitae)

Arbor Vitae

• In latin “ tree of life” it is the white matter of cerebellum.

• Tree like appearance.

• It brings sensory and motor sensation to and from cerebellum.

Main Fissures

3 Main Fissure:

1. Primary fissure
   – V-shaped fissure
   – Superior surface of cerebellum
2. Horizontal fissure – Located along the margin of the cerebellum
   – separates the superior from the inferior surfaces
   – Inferior surface of cerebellum

• The deepest fissures (primary & uvulonodular) divide cerebellum into 3 lobes:

– Anterior lobe
= ant to the primary fissure
– Posterior/middle lobe
= between ant & uvulonodular fissures & Largest
– Flocculonodular lobe

• Ant & post/middle lobes = formed the corpus cerebelli

Cerebellum Peduncles

• CEREBELLUM is one of the three major motor control centres of the brain.
• Motor control centres:
  –Cerebral cortex
  –Basal ganglia
  –Cerebellum
• The term cerebellum is from Latin = little brain.
• In adults the weight ratio between cerebellum and cerebrum is 1:10, Infants 1:20

• Is the largest part of the hindbrain
• Functions:
  – Entirely motor
  – Operates at an unconscious level
  – Controls maintenance of equilibrium (balance)
  – Influences posture and muscle tone
  – Coordinates movement
• It originates from the dorsal part of the brain stem

• Connected to the brain stem by 3 symmetrical bundles of nerve fibers

• Cerebellar peduncles fiber tracts that communicate with other parts of brain

– Superior peduncle : to midbrain
– Middle peduncle : to pons
– Inferior peduncle : to medulla oblongata