cerebellum by dr.sidra

Learning Objective

• Describe the functions of Cerebellum

• Clinical abnormalities

• Originate from inferior olive

• 1 fibre/5-10 purkinje cells

• Single impulse -Complex spike

• Enter from multiple sources

• Synapse with 100 to 1000 granule cells

– Weak synaptic

connections – More fibers

– Activation – Simple

Spikes

Glomerulus

Neurons and Circuits of the Cerebellum

Purkinje cells:

• Purkinje cells:

– 50 to 100 AP per second

• Deep nuclear cells at much higher rates

• Direct stimulation of deep nuclear cells –Excites them

• Signals from Purkinje inhibits them

Vestibulocerebellum • Importance in maintaining balance

• Performance of rapid movements

– Change in direction

– Balance b/w agonist and antagonist muscles

• Problem is of time

– Most rapid conduction = 120 m/s --- 10 -15 millisec

– 10 inches movement occurred…………

– IMPOSSIBLE –RETURNING SIGNALS REACH AT TIME OF MOVEMENT

– Signals from periphery –

• Tell brain the rate and direction of movement

• Vestibulocerebellum Calculate In

Advance

• INFORMATION FROM PERIPHERY AND VESTIBULAR

APPARATUS

• For anticipatory correction of postural motor signals– Necessary for maintaining equilibrium

• Peripheral body parts feedback through Vermis– Vestibulocerebellum help brain stem

• Vestibular nuclei• Reticular nuclei

– Compute required position of respective parts of body

VESTIBULOCEREBELLUM

• MUSCLE TONE

• EQUILIBRIUM

• BALANCE

• EYE MOVEMENTS

Spinocerebellum

• Provide smooth coordinate movements of agonist and antagonist muscles for– Acute purposeful patterned movements

• Cerebellum comparesIntentions of cerebral cortex

WithPerformance of respective parts of body

Main connections of spinocerebellum

SPINOCEREBELLUM

• TONE

• SYNERGY OF MOVEMENT

• POSTURE

• LOCOMOTION

ROLE OF OLIVARY

AND PURKINJE SYSTEM

Prevent overshoot and Damp movements

• Because of momentum

– All body movements are pendular

– All movements have tendency to overshoot

• Appropriate learned subconscious signals from

intact cerebellum stop movement precisely at

intended point

1. Provide damping

2. Prevent tremors and overshoot

Cerebellar control of Ballistic movements

• Typing movements Ballistic movements• Scanning with eyes Saccadic movements

• If cerebellum removed:

– Movements slow to develop

– Force development is weak

– Movements are slow to turn off

Because there is

– No first excitatory and then delayed inhibitory signal by

cerebellum……

Cerebro cerebellum• Lateral zone highly developed and enlarged

• Movements of hand & fingers and speech

performed

• No

– Direct information from periphery of body

– Direct contact with primary motor cortex

• But with premotor and association

areas

• If destroyed

– In-coordinate hand/finger movements?

– Speech is in-coordinate?

Cerebro cerebellum

1. Planning of sequential movements

2. Timing of sequential movements

3. Extra motor predictive function

4. MOTOR LEARNING & COGNITIVE

ROLE

Planning of sequential movements

• Planning of sequential movement - Dentate

Nuclei

• Start in sensory and premotor areas of cortex

• Transmitted to lateral zones of cerebellum

• Appropriate motor signals provide

transition from one movement to other

• Involved in PLAN of future movement

Timing of sequential movements

• Provide appropriate timing for each movement

• Person recognize the need

• Predict ahead of time, how far different parts of

body will move in given time

• Smooth progression of movement

• If damaged : • Writing, Running, Speech uncoordinated

Extra motor predictive function

• Rates of progression of visual and auditory

phenomenon

– Predicted by brain

–Need Cerebellum

• If large lateral portions of cerebellum of

monkey removed?

Clinical abnormalities

– Dysmetria– Overshoot– Ataxia– Past pointing– Dysdiadochokinesia– Dysarthria(scanning speech)– Decomposition of movements– IntentionTremor

– Cerebellar Nystagmus– Hypotonia– Rebound phenomena– Asynergia– Asthenia– Astasia– Postural changes and disturbance of gait– Disturbance in reflexes