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Nervous System Physiology By Dr. SHAHAB SHAIKH PhD MD MBBS Lecture – 8: Cerebellum •••••••••••••••••••••••••••••••••• Faculty of Medicine Al Maarefa Colleges of Science & Technology CEREBELLUM • Cerebellum - Latin for "little brain" • Neurons found in cerebellum are approximately four times more than that are present in the rest of brain. 2 CEREBELLAR FUNCTIONS 1) Maintenance of balance 2) Enhancement of muscle tone 3) Coordination and planning of skilled voluntary muscle activity 4) Sequences the motor activities= also function of premotor area= cerebrum 5) Monitors and makes corrective adjustments in the activities initiated by other parts of the brain 6) Compares the actual motor movements with the intended movements and makes corrective changes. 7) The cerebellum does not initiate movement, but it contributes to coordination, precision, and accurate timing.= like the fun of Basal Ganglia 3 Functional Organization of the Cerebellum Functionally cerebellum can be divided into . . . • The Floculonodular lobe – Vestibulocerebellum – participates mainly in balance and spatial orientation • Intermediate zone - Spinocerebellum – Enhances muscle tone and coordinates skilled voluntary movements • Lateral zone - Cerebrocerebellum – controls sequencing movements of the muscle. Important for timing and coordination of movement. – Plays role in planning and initiating voluntary activity – Stores procedural memories= learned movement 4 Neuronal Organization of the Cerebellar Cortex Cerebellar Cortex is organized in three layers – Molecular layer – Purkinje cell layer – Granular cell layer 5 Neuronal Organization of the Cerebellar Cortex Cerebellar Cortex is organized in three layers I. Granular layer – It is thick inner most layer and contains Granule cells, Golgi type II cells and other interneurons( largest # on neuron , max neurons) II. Purkinje cell layer (lots of dendrites, one axon) – – – It is middle layer Contains Purkinje cells Output is always Inhibitory(secret GABA) III. Molecular layer – – It is outermost layer Contains stellate and basket cells, dendrites of Purkinje and Golgi type II cells and parallel fibers (axons of granule cells) 6 Neuronal Organization of the Cerebellar Cortex Purkinje cell: • Purkinje cells are among the most distinctive neurons in the brain • The dendrites branch very profusely. The dendrites are covered with dendritic spines which receives synaptic input from a parallel fiber. • Their axons travel into the deep cerebellar nuclei. • Purkinje cells use GABA as their neurotransmitter, and therefore exert inhibitory effects on their targets. 7 Neuronal Organization of the Cerebellar Cortex Granule cell: • Granule cells are among the smallest neurons in the brain. • They are the most numerous neurons in the brain; about 3/4 of the brain's neurons are cerebellar granule cells. • A granule cell receives excitatory input from mossy fibers and inhibitory input from Golgi cells on its ‘Dendritic Claw’. • The axons of granule cells rise vertically to the molecular layer, where they form parallel fibers, synapsing with Purkinje dendrites. • The neurotransmitter is Glutamate and is excitatory. 8 Neuronal Organization of the Cerebellar Cortex Three types of axons play dominant roles: I. Mossy fibers input – – enter the cerebellum from outside II. Climbing fibers input – Inf Olivary nucleus – enter the cerebellum from outside – project to Purkinje cells and also collaterals directly to the deep nuclei send III.Parallel fibers – are the axons of granule cells present in molevular layer 9 Neuronal Organization of the Cerebellar Cortex Mossy fibers: – Originate from brain stem and spinal cord Includes Vestibulocerebellar, Spinocerebellar and Pontocerebellar afferents. – Form excitatory synapses with the Granule cells and the cells of the deep cerebellar nuclei. 10 Neuronal Organization of the Cerebellar Cortex Climbing Fibers: – Originate from inferior olivary nucleus of contralateral side in the medulla. – Gives Collaterals to Deep Cerebellar Nuclei and make multiple synapses on Purkinje cells. – Each Purkinje cell receives input from exactly one climbing fiber; but this single fiber "climbs" the dendrites of the Purkinje cell, winding around them and making multiple synapses. – Play role in cerebellar motor learning. 11 Circuit of the Cerebellum Thus in Summary …. Output of the Cerebellar cortex • Purkinje cells are the only output of the cerebellar cortex which goes to Deep cerebellar Nuclei • Output of the Purkinje cells is always inhibitory. the neurotransmitter is γ- aminobutyrie acid (GABA) • Output of the cerebellum regulates rate, range and direction of movement. Input to the Cerebellar cortex • From Mossy fibers originating from brain stem and spinal cord • From Climbing fibers originating from Inferior Olivary Nucleus in Medulla 12 Circuit of the Cerebellum Explanation will be in the next slide Deep nuclear cells receive excitatory and inhibitory inputs Inhibitory from Purkinje cells Excitatory afferent inputs from climbing fibers and mossy fibers 13 Circuit of the Cerebellum What ever info is coming in (climbing or mossy) One copy goes to nucleus of cerebellum One copy goes to molecular layer to form parallel fiber (analyze the info) The result will be sending info back to nucleus will be inhibitory **( increase or decrease inhibition) 14 Deep Cerebellar Nuclei • These are clusters of gray matter lying within the white matter at the core of the cerebellum. • These nuclei receive collateral projections from mossy fibers and climbing fibers as well as inhibitory input from the Purkinje cells of the cerebellar cortex. • There are four nuclei … 1. 2. 3. 4. Dentate: communicates exclusively with the lateral parts of the cerebellar cortex. Globose: Emboliform Fastigial • These nuclei are the sole sources of output from the cerebellum except for the Floculonodular lobe which does not project to the deep nuclei—its output goes to the vestibular nuclei instead.(works like cerebellum nuclei) 15 Afferent Pathways to the Cerebellum from the periphery … • Dorsal spinocerebellar tract fastest neruons in body • transmits information mostly from muscles spindle but also from Golgi tendon organs, tactile, and joint receptors • apprises the brain of the momentary status of muscle contraction, muscle tension and limb position and forces acting on the body surface • Ventral spinocerebellar tract • signals from anterior horn, and interneurons • transmits information about which signals have arrived at the cord 16 Peduncle Description SUPERIOR The superior cerebellar peduncle is the major output = Efferent pathway of the cerebellum. Most of the efferent fibers originate within the dentate nucleus which in turn project to MIDDLE Input This is composed entirely of afferent fibers. INFERIOR Output Clinical Signs In Cerebellar Disease **U have to know the def of each one** • Ipsilateral control • Drunken gait – wide based, unsteady gait • يمشي كأه سكران • Nystagmus – Rhythmic, oscillating eye movements • عيونه تتحرك بسرعةrapid jerky eye movement • Hypotonia - Reduced muscle tone but no paralysis • Dysdiadokokinesia - Inability to perform rapid alternate movements smoothly هنا مارح يقدر, مثل تشوفي صرصور وتتحركي بسرعة لما ً ا • Intention tremor – tremors on activity • Dysmetria - patients overshoots intended target • ما يقدر يحسب المسافة بين رجله واالرض • Dysarthria - Scanning, slurred speech • كلم متلعثم مو مفهوم 18 Clinical Signs T – ANDDD • • • • • • T – Tremor (intention) A – Ataxia N – Nystagmus D – Dysarthria D – Dysdiadokokinesia D – Dysmetria 19