Cerebellum

Front 1

Function of the cerebellum

Back 1

1. maintenance of posture & balance
2. Maintenance of muscle tone
3. Coordination of voluntary motor activity

Front 2

Superior Cerebellar Peduncle

Back 2

- major OUTPUTS from cerebellum
- DENTATOTHALAMIC tract that terminates in the VL thalamus (decussation in the caudal midbrain tegmentum
- ONE major afferent Ventral SptT

Front 3

Middle Cerebellar Peduncle

Back 3

RECIEVES pontocerebellar fibres PROJECTS to neocerebellum

Front 4

INFERIOR cerebellar peduncle

Back 4

3 MAJOR afferents
1. DscT
2. Cuneocerebellar tract
3. Olivocerebellar tract (form contralateral inferior olivary nucleus)

Front 5

Cerebellar Cortex

Back 5

3 layers
1. Molecular layer (stellate, basket cells & dendritic arbor of the purkinje cells)
2. Purkinje Cell layer lies between the 2 layers
3. Granule layer inner layer overlying the white matter (granule cells, golgi cells and cerebellar glomeruli)

Front 6

Neurons & Fibres of the cerebellum

Back 6

1. purkinje cells: outputs from cerebellar cortex. inhibitory GABA to cerebellar & vestibular nuclei
2. Granule cells: glutamanergic excitatory cells
3. Parallel fibres; axons of granule cells that extend into the molecular layer
4. Mossy fibres are afferent excitatory fibres of the Spc, Pontocerebellar & vestibulocerebellar Tracts, terminating on granule cell, exciting them then dischargin through parallel fibres
5. Climbing fibres are afferent excitatory (ASP) from olivocerebellar tract

Front 7

Major Cerebellar Pathway

Back 7

1. Purkinje cells of the cerebellar cortex ptoject to cerebellar nuclei
2. Dentate Nucleus
3. VL thalamus to 1o motor cortex
4. Motor cortex as corticopontine tract to pontine nuclei
5. Pontine Nuclei project as pontocerebellar tract to contralateral cerebellar cortex where they terminate as mossy fibres completing the circuit

Front 8

Denate Nucleus

Back 8

effector nucleus giving rise to DENTATOTHALAMIC tract

Front 9

Principal Cerebellar Connections

Back 9

Front 10

Cerebellar Dysfunction;
Tirad

Back 10

(think alcoholic)
1. hypotonia (rag-doll appearance with pendular reflexes)
2. Dysequilibrium (loss of balance affecting gait and trunk dystaxia)
3. Dyssynergia (loss of coordinated muscle activity
- dysmetria
- intention tremor
- failure to check movements
- nystagmus (coarse and worse when looking towards side of the lesion)
- dysdiadochokinesia
- dysrhythmokinesia

Front 11

Anterior Vermis Syndrome

Back 11

- involves leg region of anterior lobe
- atrophy of the rostral vermis most commonly due to Alcohol abuse
- causes gait, trunk & leg dystaxia

Front 12

Posterior Vermis Syndrome

Back 12

- flocculonodular lobe
- causes truncal dystaxia
- due to brain tumours

Front 13

Hemispheric Syndrome

Back 13

- one cerebellar hemisphere
- DUE to brain tumor or abscess (2o to otitis media or mastoiditis)
- causes arm, leg, gait dystaxia & ipsilateral cerebellar signs

Front 14

Cerebellar Tumors

Back 14

- 70% of brain tumor in children are found in the post. fossa
- 70% in adults are supratentorially
1. Astrocytomas (30% children) most often in cerebellar hemispheres
2. Medulloblastomas; (20%) and are malignant. believed to orginate from granular layer, and obstruct the CSF flow causing hydrocephalus
3. Ependymomas (15%) fq in 4th ventricle

Front 15

Cerebellum Blood Supply

Back 15

Blood supply from posterior inferior and the anterior
inferior cerebellar arteries (PICA and AICA) and from
the superior cerebellar artery (SCA, all vertebral artery system).

Front 16

Cerebellum Landmarks

Back 16

arbor vitae,
culmen,
primary fissure,
fastigium

Front 17

Cerebellum Anatomy

Back 17

Front 18

Peduncular surface

Back 18

Front 19

Lobes

Back 19

Front 20

Structure and function

Back 20

Front 21

Deep Cerebellar Nuclei

Back 21

Front 22

Circuitry of cerebellum (simplified

Back 22

There is considerable amount of crossing in the case of vestibulocerebellum (e.g. uncinate fasciculus) meaning that vestibulocerebellar lesions are likely to produce bilateral deficits.

Front 23

Molecular layers of Cerebellum

Back 23

Front 24

Mossy Fibres

Back 24

• Mossy fibres (excitatory; +), bifurcate many times and form “rosettes”.
• Each rosette synapses with about 20 granule cells
• Granule cells produce parallel fibres (excitatory; +)
• Parallel fibres (PF) contact Purkinje cells (PC) and basket cells (BC, inhibitory)
• Each PF fires the PC in its path and inhibits the PC in the path of the PF next to it: the most excited parallel
fibre will win!
• PF also contact Golgi cells which send inhibitory feedback to the rosette and cut off the signal
• Result: sharpening of the signal in space and time (digitization?)

-160,000 paralell fibres/ purkinje cell
- * inhibitory to PC’s in the neighbouring rows, i.e. not quite as the picture shows.

Front 25

Cerebellar cytoarchitecture

Back 25

Front 26

Climbing Fibres

Back 26

coming form the contralateral inferior olivary comples contact between 2/10PC
- each PC recieves only one CF
- repeated firing of CF will slow down the activity of PC "long term depression" LTD cerebellar LEARNING?

Front 27

Only output form cerebellar cortex via

Back 27

-PC
- GABAergic inhibitory cells

Front 28

Dentate; projection (Cerebrocerebellum)

Back 28

contralateral VL n, then cortex

Front 29

Globose, emboliform, fastigal (spinocerebellum)

Back 29

to contralateral red nucleus and RF

Front 30

Lateral vestibular (deiters)n (vestibulocerebellum

Back 30

vestibulospinal tract and RF

Front 31

PROPOSED MOA of cerebellum

Back 31

• Removing “noise” from processed signals (“sharpening in time and space”)
• Comparing intended and executed movement (most likely including
spinocerebellum).
• Making the “right” signals long-lasting (“cerebellar learning” or “cerebellar
programming”): Long term depression (LTD) and other mechanisms

Front 32

Compare Basal Ganglia to Cerebellum

Back 32

BG:
1. input from prefrontal cortex output focused on supplementary motor areas
2. conscious initiation and lannning of movement
C
1. wider input, output focused of area 4 (primary motor)
2. preprogrammed automated movements

Front 33

Cerebellum lesions and associated deficits

Back 33

• Archicerebellum: Unsteadiness, swaying, falling. Tendency to fall backwards
when walking. Muscle tone not changed all the time. No asynergy or tremor in the
limbs. Signs are usually bilateral.
• Paleocerebellum: no specific deficits known in humans but could be similar to
decerebration in animal experiments.
• Neocerebellum (incl. paravermal regions i.e. parts of spinocerebellum): loss of
muscle tone and fatigue, asynergia, dysmetria (hypermetria, pastpointing),
intention tremor, dysdiadochokinesia (inability to perform rapid successive
movements), nystagmus, speech disturbances (slurred speech, separating of
syllables).

Front 34

Main functions of cerebellum

Back 34

• Maintaining posture and balance while standing and moving (vestibulocerebellum).
• Monitoring the movement as it is executed (spinocerebellum)
• Coordinating synergy of mucle activity in groups of muscles to generate complex
movements (cerebrocerebellum)
• Integrating of sensory input to help to plan and execute complex and precise
movement essential in activities such as sports or playing musical instruments
(spinocerebellum, visuocerebellum, audiocerebellum, very probably
cerebrocerebellum, too). Automation of such movements through cerebellar
“learning” (cerebellum as a computer?).
• Automation of complex mental activities (calculus)?
• Involvement of cerebellum in emotions, cognition, language..???*