Cerebellum😊

Parts & Functions

Part	Function
Cerebrocerebellum (Lateral)	• Planning and timing of movement • Lesion: I/L Limb ataxia
Spinocerebellum (Intermediate + Vermis)	• Smoothening and coordination of movement • Lesion: Truncal ataxia/ Proximal limb
Vestibulocerebellum (Flocculonodular)	• Vestibular reflex, balance, and posture • If affected: ↳ Alcoholic gait and Nystagmus

Cerebellar lesions

Cerebellar Lesions – DANISH

• D: Dysarthria, Dysmetria, Decomposition of movement

• A: Truncal Ataxia (drunken gait)
• Wide based stance

• N: Nystagmus
• Kinetic /Intention tremor (during voluntary movement)
• Seen with activity.
• Absent at rest.
• Titubation 
• Tremors of head

• I: Incoordination / Intention tremor

• S: Slurring or scanning speech

• H: Hypotonia

Others

• Past pointing (Finger-nose test)

• Pendular knee jerk

• Dysdiadochokinesia:
• Inability to perform alternating supination and pronation movements.

• Rebound phenomenon:
• Unable to stop the movement.

Note:

• No sensory deficit

• No abnormality at rest

Note

Posterior column defect

• Stomping gait

• Inability to walk with eyes closed

Layers of Cerebellar Cortex

• Climbing fibers
• Olivocerebellar
• Para-olivocerebellar tract

• Rest all → MOSY

• Cerebellar cortex:
• Largest collection of inhibitory neurons
• Only Excitatory cell → Granular

• Only efferent from cortex
• Purkinje cells
• Flask-shaped, largest

Afferents of Cerebellum

• Climbing fibers
• Up to molecular layer.
• Originate from: Inferior Olivary Nucleus
• Olivocerebellar tract.
• Para olivocerebellar tract.
• Mnemonic: Oli → Cli

• Mossy fibers
• Up to granular layer only.
• Originate from:
• All other tracts
• Mossy fibers + granular cells → form cerebelloglomeruli

Efferent of Cerebellum

• Efferent from cerebellar cortex
• Comes from Purkinje cells.
• Purkinje cells ⛔ deep nuclei of cerebellum via GABA.
• This inhibition fine-tunes cerebellar output, regulating:
• Timing.
• Force.
• Coordination of movements.

• Efferent from cerebellum
• Originates from deep nuclei

Cerebellar Peduncles

• Mnemonic:
• Superior peduncle → Superior () Villain (VL nucleus → Dental Dr)
• Middle peduncle → Middle of night → Watch porn → So Monitor the activity (Corticospinal)

Middle Cerebellar Peduncle

• Largest Peduncle

• Purely afferent

• From contralateral cortex
  

Questions

Q. Fiber’s from the marked structure terminates at which of the following?

A. Fastigial nucleus
B. Inferior olivary nucleus
C. Red nucleus
D. Subthalamus

ANS

Red nucleus

Deep Nuclei of Cerebellum

1. D - Dentate nucleus
• largest nucleus
• lateral most
• Crumpled paper bag shaped

2. E - Emboliform nucleus

3. G - Globose nucleus

4. F - Fastigial nucleus (medial most)
• Aka Nucleus of Archaecerebellum

• Mnemonic: Doctors Eat Good Food

• Emboliform + Globose nuclei = Interpositus nucleus

Start-Stop Signal Circuit (Cerebellum)

• Overall Pathway
• Sensory input → Cerebellum → Motor output

Start Pathway – Movement starts

• Inferior olivary nucleus → Climbing fibers (Excitation) → Deep cerebellar nuclei (Excitation) → Brain stem & Thalamus (Excitation) → Cerebral cortex → Movement starts

• Example: Archer pulls bow string.

Stop Pathway – Movement stops

• Inferior olivary nucleus → Climbing fibers (Excitation) → stimulate Purkinje cells (Inhibition) → ⛔ Deep cerebellar nuclei → Movement stops

• Reason: ⛔ Deep Cerebellar Nuclei (DCN)

• Example: Archer releases string.

Pre-start Pathway – Prepares for new movement

• Spinal cord → Mossy fibers
• Mossy fibers branch to:
• Ventral Spinocerebellar tract (Superior cerebellar peduncle)
• Dorsal Spinocerebellar tract (Inferior cerebellar peduncle)

• ⛔ Purkinje cells → activate Deep cerebellar nuclei

• If DCN inhibition is removed → New movement can start (via start pathway)

• Example: Archer pulls string again after release.