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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