Cerebellum – Divisions & Functions

Cerebellum – Divisions & Functions


CEREBELLUM

  • Largest part of hind brain
  • Situated in posterior cranial fossa beneath tentorium cerebelli.
  • Embryologically cerebellum is derived from Metancephalon

DIVISIONS:

Cerebellum is divided by,

1. Transverse fissures into three lobes:

  • Anterior lobe
  • Posterior lobe 
  • Flocculonodular (lateral flocculus & medial nodulus)

2. Two longitudinal fissures into 3 parts:

  • Midline vermis
  • Left cerebellar hemisphere
  • Right cerebellar hemisphere
  • Two hemispheres are joined by vermis.
ATTACHEMENTS:

 To Medulla – 

  • By three cerebellar peduncles
PARTS OF CEREBELLUM:
  • External cerebellar cortex 
  • Deep cerebellar nuclei
  • Separated by white matter.
1. Deep cerebellar nuclei:

Four nuclei – From lateral to medial

  • Dentate
  • Emboliform
  • Globose
  • Fastigial
  • Globose & Emboliform are sometimes lumped together
  • Referred as “Interpositus nucleus”
2. External Cerebellar cortex:

Five types of neurons

  • Purkinje cells
  • Granule cells
  • Basket cells
  • Stellate cells
  • Golgi cells
3. Layers of cerebellar cortex:
  • External molecular layer – Basket cells & stellate cells.
  • Middle Purkinje cell layer – Purkinje cells
  • Inner granular layer – Granular cells & Golgi cells

4. Input & output units:

Input afferent from 2 types of fibers:

Climbing fibers – 

  • From inferior olivary nuclei only

Mossy fibers – 

  • From all other parts of body

Output efferent to:

  • Axons of Purkinje cells are the only output from cerebellar cortex.
  • Generally pass through deep nuclei.
  • Deep Nucleus – Ultimate & final efferent ouput of cerebellum.
FUNCTIONAL DIVISION OF CEREBELLUM:

3 parts,

  • Vestibulocerebellum/ Flocculonodular lobe
  • Spinocerebellum
  • Cerebrocerebellum/ Neocerebellum

1. Vestibulocerebellum/Flocculonodular lobe:

  • Parts: Flocculus & Nodulus
Connections:

Receives afferents –  

  • From vestibular apparatus

Sends efferents – 

  • To Vestibular nuclei
  • Direct connection to vestibular nuclei without involvement of deep nuclei

Functions:

Works with vestibular apparatus to,

  • Modulate muscular activity to achieve postural equilibrium/balance.
  • Vestibulo-ocular reflex – Coordinate movements of eyes with movements of head

2. Spinocerebellum:

  • Consistes of Vermis & medial portion of cerebellar hemisphere
  • Proprioceptive information from body & copy of “Motor Plan” from motor cortex.

Functions:

  • Compares plans
  • Smoothens & coordinates ongoing movements
3. Cerebrocerebellum/ Neocerebellum:
  • Large lateral portion of cerebellar hemisphere
  • Newest from a phylogenetic point of view 
  • Therefore “Neocerebellum”.
Functions:
  • Interact with motor cortex in planning & programming movements
4. Corresponding neuronal circuits:
  • Vestibulocerebellar output passes directly to brainstem.
  • From cerebellar cortex to brainstem.
  • Without involvement of deep cerebellar nuclei.
  • Spinocerebellum & cerebro-cerebellum projects to deep nuclei & then to brainstem.
  • Deep nuclei provide the only output for Spinocerebellum & cerebro-cerebellum.
FUNCTIONS OF CEREBELLUM:
  • Co-ordination of movements
  • Regulation of tone, posture & equilibrium
  • Smoothening & coordination of voluntary movements.
  • Coordination of eye movements
  • Planning & initiation of movements
  • Learning of frequently performed voluntary movements.

Timing & comparison:

  • Cerebellum – Timing device
  • Times duration of agonistic muscle activity & latency of antagonistic activity
  • Ensures halting movement at correct point.
Exam Question
 

CEREBELLUM

  • Embryologically cerebellum is derived from Metancephalon

DIVISIONS:

  • Cerebellum is divided by,

1. Transverse fissures into three lobes:

  • Anterior lobe
  • Posterior lobe 
  • Flocculonodular (lateral flocculus & medial nodulus)

2. Two longitudinal fissures into 3 parts:

  • Midline vermis
  • Left cerebellar hemisphere
  • Right cerebellar hemisphere
  • Two hemispheres are joined by vermis.
ATTACHMENTS:

Medulla – 

  • By three cerebellar peduncles

PARTS OF CEREBELLUM:

  • External cerebellar cortex 
  • Deep cerebellar nuclei
1. Deep cerebellar nuclei:

Four nuclei – From lateral to medial

  • Dentate
  • Emboliform
  • Globose
  • Fastigial
  • Globose & Emboliform are sometimes lumped together
  • Referred as “Interpositus nucleus”
2. External Cerebellar cortex:

Five types of neurons

  • Purkinje cells
  • Granule cells
  • Basket cells
  • Stellate cells
  • Golgi cells
3. Layers of cerebellar cortex:
  • External molecular layer – Basket cells & stellate cells.
  • Middle Purkinje cell layer – Purkinje cells
  • Inner granular layer – Granular cells & Golgi cells

4. Input & output units:

Input afferent from:

Climbing fibers – 

  • From inferior olivary nuclei only.

Mossy fibers – 

  • From all other parts of body

Output efferent to:

  • Axons of Purkinje cells are the only output from cerebellar cortex.
  • Deep Nucleus – Ultimate & final efferent output of cerebellum.
FUNCTIONAL DIVISION OF CEREBELLUM:

3 parts,

  • Vestibulocerebellum/ Flocculonodular lobe
  • Spinocerebellum
  • Cerebrocerebellum/ Neocerebellum

1. Vestibulocerebellum/Flocculonodular lobe:

Parts: 

  • Flocculus & Nodulus
Connections:

Receives afferents –  

  • From vestibular apparatus

Sends efferents – 

  • To Vestibular nuclei
  • Direct connection to vestibular nuclei without involvement of deep nuclei

Functions:

Works with vestibular apparatus to,

  • Modulate muscular activity to achieve postural equilibrium/balance.
  • Vestibulo-ocular reflex – Coordinate movements of eyes with movements of head

2. Spinocerebellum:

Functions:

  • Compares plans.
  • Smoothens & coordinates ongoing movements
3. Cerebrocerebellum/ Neocerebellum:
  • Large lateral portion of cerebellar hemisphere
  • Newest from a phylogenetic point of view 
  • Hence, “Neocerebellum”.
Functions:
  • Interact with motor cortex in planning & programming movements
4. Corresponding neuronal circuits:
  • Vestibulocerebellar output passes directly to brainstem.
  • From cerebellar cortex to brainstem without involvement of deep cerebellar nuclei.
FUNCTIONS OF CEREBELLUM:
  • Co-ordination of movements
  • Regulation of tone, posture & equilibrium
  • Smoothening & coordination of voluntary movements
  • Coordination of eye movements
  • Planning & initiation of movements.
  • Learning of frequently performed voluntary movements.

Timing & comparison:

  • Cerebellum – Timing device.
  • Times duration of agonistic muscle activity & latency of antagonistic activity.
  • Ensures halting movement at correct point.
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