CEREBELLUM – DIVISIONS & FUNCTIONS
- 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.
- To Medulla –
– By three cerebellar peduncles
- External cerebellar cortex
- Deep cerebellar nuclei
- Separated by white matter.
- Four nuclei – From lateral to medial
– Dentate
– Emboliform
– Globose
– Fastigial
- Globose & Emboliform are sometimes lumped together
- Referred as “Interpositus nucleus”
- Five types of neurons
– Purkinje cells
– Granule cells
– Basket cells
– Stellate cells
– Golgi cells
- 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.
- 3 parts,
– Vestibulocerebellum/ Flocculonodular lobe
– Spinocerebellum
– Cerebrocerebellum/ Neocerebellum
1. Vestibulocerebellum/Flocculonodular lobe:
- Parts: Flocculus & Nodulus
- 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
- Large lateral portion of cerebellar hemisphere
- Newest from a phylogenetic point of view
- Therefore “Neocerebellum”.
- Interact with motor cortex in planning & programming movements
- 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.
- 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 Important
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.
- Medulla –
– By three cerebellar peduncles
PARTS OF CEREBELLUM:
- External cerebellar cortex
- Deep cerebellar nuclei
- Four nuclei – From lateral to medial
– Dentate
– Emboliform
– Globose
– Fastigial
- Globose & Emboliform are sometimes lumped together
- Referred as “Interpositus nucleus”
- Five types of neurons
– Purkinje cells
– Granule cells
– Basket cells
– Stellate cells
– Golgi cells
- 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.
- 3 parts,
– Vestibulocerebellum/ Flocculonodular lobe
– Spinocerebellum
– Cerebrocerebellum/ Neocerebellum
- Flocculus & Nodulus
- 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
- Large lateral portion of cerebellar hemisphere
- Newest from a phylogenetic point of view
- Hence, “Neocerebellum”.
- Interact with motor cortex in planning & programming movements
- Vestibulocerebellar output passes directly to brainstem.
– From cerebellar cortex to brainstem without involvement of deep cerebellar nuclei.
- 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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