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
Spinocerebellum• Provide smooth coordinate movements of agonist and antagonist muscles for – Acute purposeful patterned movements• Cerebellum compares Intentions of cerebral cortex With Performance of respective parts of body
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• Provide damping• 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• Planning of sequential movements• Timing of sequential movements• Extra motor predictive function• 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