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Cerebellum 10 th Lecture Cerebellum Anatomy Function Clinical points

3 Cerebellum - The cerebellum plays a very important role in the control of posture and voluntary movements - It unconsciously influences the smooth contraction of voluntary muscles and carefully coordinates their actions, together with the relaxation of their antagonist -Each cerebellar hemisphere controls muscular movements on the same side of the body - Cerebellum has no direct pathway to the lower motor neurons but exerts its control via the cerebral cortex and the brainstem

Cerebellum Largest part of hindbrain Located in posterior cranial fossa Lies posterior to 4 th ventricle, pons and medulla oblongata Ovoid in shape and constricted in median part

Cerebellar Connections Connected to posterior aspect of brain stem by: –Superior cerebellar peduncle –Middle cerebellar peduncle –Inferior cerebellar peduncle

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Cerebellar Lobes It is divided into 3 lobes –Anterior –Middle or posterior –Flocculonodular. by 2 fissures: Primary & Uvulonodular Horizontal fissure (H.F. is of no physioloical and functonal importance)

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Cerebellar Connections Connected to posterior aspect of brain stem by: –Superior cerebellar peduncle –Middle cerebellar peduncle –Inferior cerebellar peduncle

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Structure of Cerebellum Cortex Intracerebellar nuclei

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Structure of cortex It is a large sheet of transverse (coronal) lying folds or folia Each fold or folium made by a core of white matter covered superficially by gray matter A median plane section through cerebellum divides folia at right angles which has a branched appearance called ; arbor vitae which is in the coronal section

Cellular organization of cerebellar cortex Molecular layer –Basket cells (Inhibitory interneuron) –Stellate cells (Inhibitory interneuron) Purkinje cell layer (center of functional unit of cerebellar cortex) Granular layer –Granular cells (excitatory interneuron) –Golgy cells (Inhibitory interneuron)

Structure of the Cerebellar Cortex -folium -arbor vita

Functional Areas of the Cerebellar Cortex The cortex of the vermis influences the movements of the long axis of the body namely the neck, the shoulders the thorax, the abdomen, and the hips. Immediately lateral to the vermis is a so-called intermediate zone of the cerebellar hemisphere.This area has been shown to control the muscles of the distal parts of the limbs, especially the hands and feet. The lateral zone of each cerebellar hemisphere appears to be concerned with the planning of sequential movements of the entire body and is involved with the conscious assessment of movement errors.

Intracerebellar nuclei Dentate Emboliform Globose Fastigial

Dentate Fastigial Emboliform Golobose The intracerebellar nuclei are composed of large, multipolar neurons with simple branching dendrites. The axons form the cerebellar outflow in the superior and inferior cerebellar peduncles.

The dentate nucleus is the largest of the cerebellar nuclei. It has the shape of a crumpled bag with the opening facing medially. The interior of the bag is filled with white matter made up of efferent fibers that leave the nucleus through the opening to form a large part of the superior cerebellar peduncle. The fastigial nucleus lies near the midline in the vermis and close to the roof of the fourth ventricle; it is larger than the globose nucleus

White matter Intrinsic fibers Afferent fibers Efferent fibers

White matter Intrinsic fibers - The intrinsic fibers do not leave the cerebellum but connect different regions of the organ. - Some interconnect folia of the cerebellar cortex and vermis on the same side - Others connect the two cerebellar hemispheres together.

White matter Afferent fibers - The afferent fibers form the greater part of the white matter and proceed to the cerebellar cortex. - They enter the cerebellum mainly through the inferior and middle cerebellar peduncles

38 White matter Efferent fibers - The efferent fibers constitute the output of the cerebellum and commence as the axons of the Purkinje cells of the cerebellar cortex. - The great majority of the Purkinje cell axons pass to and synapse with the neurons of the cerebellar nuclei (fastigial,globose,emboliform,and dentate) the axons of the neurons then leave the cerebellum. - A few Purkinje cell axons in the flocculonodular lobe and in parts of the vermis bypass the cerebellar nuclei and leave the cerebellum without synapsing. - Fibers from the dentate, emboliform,and globose nuclei leave the cerebellum through the superior cerebellar peduncle. - Fibers from the fastigial nucleus leave through the inferiorc erebellar peduncle

White matter Intrinsic fibers Afferent fibers which are excitatory to purkinje cells –Climbing fibers (olivocerebellar fibers) –Mossy fibers (all other afferents) Efferent fibers (purkinje cell axons)

Cerebellar Cortical Mechanisms 1385Isfahan University of Medical Sciences40 - The climbing and the mossy fibers constitute the two main lines of input to the cortex and are excitatory to the Purkinje cells - The climbing fibers are the terminal fibers of the olivocerebellar tracts - They are so named because they ascend through the layers of the cortex like a vine on a tree - Each climbing fiber wraps around and makes a large number of synaptic contacts with the dendrites of a Purkinje cell - A single Purkinje neuron makes synaptic contact with only one climbing fiber. However, one climbing fiber makes contact with 1 to 10 Purkinje neurons

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Cerebellar Cortical Mechanisms 1385Isfahan University of Medical Sciences42 - The mossy fibers are the terminal fibers of all other cerebellar afferent tracts - They have multiple branches and exert a much more diffuse excitatory effect - A single mossy fiber may stimulate thousands of Purkinje cells through the granule cells - Each climbing fiber wraps around and makes a large number of synaptic contacts with the dendrites of a Purkinje cell

What then is the function of the remaining cells of the cerebellar cortex, namely the stellate, basket, and Golgi cells? 1385Isfahan University of Medical Sciences43 - Neurophysiologic research, using microelectrodes, would indicate that they serve as inhibitory interneurons - It is believed that they not only limit the area of cortex excited but influence the degree of Purkinje cell excitation produced by the climbing and mossy fiber input - By this means, fluctuating inhibitory impulses are transmitted by the Purkinje cells to the intracerebellar nuclei, which, in turn, modify muscular activity through the motor control areas of the brainstem and cerebral cortex - It is thus seen that the Purkinje cells form the center of a functional unit of the cerebellar cortex

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Cerebellar Cortical Mechanisms 1385Isfahan University of Medical Sciences45 - The climbing and the mossy fibers constitute the two main lines of input to the cortex and are excitatory to the Purkinje cells - The climbing fibers are the terminal fibers of the olivocerebellar tracts - They are so named because they ascend through the layers of the cortex like a vine on a tree - Each climbing fiber wraps around and makes a large number of synaptic contacts with the dendrites of a Purkinje cell - A single Purkinje neuron makes synaptic contact with only one climbing fiber. However, one climbing fiber makes contact with 1 to 10 Purkinje neurons

Cerebellar Cortical Mechanisms 1385Isfahan University of Medical Sciences46 - The climbing and the mossy fibers constitute the two main lines of input to the cortex and are excitatory to the Purkinje cells - The climbing fibers are the terminal fibers of the olivocerebellar tracts - They are so named because they ascend through the layers of the cortex like a vine on a tree - Each climbing fiber wraps around and makes a large number of synaptic contacts with the dendrites of a Purkinje cell - A single Purkinje neuron makes synaptic contact with only one climbing fiber. However, one climbing fiber makes contact with 1 to 10 Purkinje neurons

Intracerebellar Nuclear Mechanisrns 1385Isfahan University of Medical Sciences47 The deep cerebellar nuclei receive afferent nervous information from two sources: 1- the inhibitory axons from the Purkinje cells of the overlying cortex 2- the excitatory axons that are branches of the afferent climbing and mossy fibers that are passing to the overlying cortex - ln this manner,a given sensory input to the cerebellum sends excitatory information to the nuclei, which a short time later receive cortical processed inhibitory information from the Purkinje cells - Efferent information from the deep cerebellar nuclei leaves the cerebellum to be distributed to the remainder of the brain and spinal cord

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White matter Intrinsic fibers Afferent fibers which are excitatory to purkinje cells –Climbing fibers (olivocerebellar fibers) –Mossy fibers (all other afferents) Efferent fibers (purkinje cell axons)

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White matter … Inferior cerebellar peduncle –PSCT –OCT –CCT –RCT –VCT Superior cerebellar peduncle Middle cerebellar peduncle

Overview Cerebral Cortex Basal Ganglia Cerebellum Brainstem Spinal Cord Thalamus head muscles body muscles

Cerebellar Functions 1. Controls balance and eye movements 2. Adjusts proximal limb muscles 3. Adjusts (coordinates) distal limb muscles

72 CNS 1- Cerebral cortex 2- Brainstem 3- Cerebellum 2- Vestibular 3- Proprioceptive 1- Visual Muscle commands Systems regulating body balance

Which part of the CNS are involved in performance of movements? Basal ganglia : –start the movements Cerebral cortex, brain stem and the spinal cord: – execute the movements Cerebellum: – coordinates and smoothes the movements

Movement Control COMPONENTFUNCTIONDEFICITS Substantia NigraStartLoss of starting, tremor & rigidity Basal GangliaControlChoreiform move. Subthalamuscontrolhemiballismus Cerebral Cortex Brainstem, Spinal cord ExecuteWeak / Paralyzed SpinocerebellumAdjustJerky (ataxia) CerebrocerebellumCoordinateAtaxia / Inaccurate VestibulocerebellumBalance / Posture Loss of balance

Mechanism of Cerebellum Origins of information: –Cerebral cortex –Muscles, tendons, joints –Vestibular system –Eye Cerebellar output: –Cerebral cortex

Cerebellar signs & symptoms The lesions are reflected ipsilateral: –Hypotonia –Pendular knee jerk –Ataxi (lack of coordinated movement) –Gait ataxia (ataxia of proximal limb muscles) –Intension tremor (ataxia of distal limb muscles) –Nystagmus (ataxia of extraocular muscles)

Cerebellar signs & symptoms continue … Dysmetria, (missing the target, finger) Dysarthria (ataxia of laryngeal muscles) Dysdiadochokinesia (impaired rapid alternative movementsts Vermis syndrome, (meduloblastoma of vermis involving flocculonodular lobe)

78 Examination of nystagmus Nystagmus = rhythmic involuntary oscillation of eyes with fast and slow phases

Connections of the vestibular sensory organs Vestibulo-Ocular reflex (VOR) Vestibulo-Spinal reflex (VSR) Vestibulo-Ocular reflex (VOR) Vestibulo-Spinal reflex (VSR)

Vestibulo-Ocular Reflex (VOR) STIMULUS = Head movement Efferent = oculomotor nerves Effector = Extra-ocular muscles Sensory = Vestibular HC Afferent = vestibular nerve Center

81 Vestibulo-Spinal Reflex (VSR) STIMULUS = Gravity linear acceleration Efferent = Spinal nerves Effector = Neck and body muscles Sensory = Vestibular HC Afferent = vestibular nerve Center

1385 Caloric testing Procedure and recording

Cerebellar Lesions Cerebellar symptoms are caused by damage to cerebellum, its peduncles or pathways. Produce motor deficits on same side of body: –Vestibulocerebellar lesions cause nystagmus and loss of balance. –Spinocerebellar lesions cause ataxic gait. –Cerebrocerebellar lesions cause limb ataxia, dysmetria, dysdiadochokinesia & tremor.

Clinical Testing Finger to nose test Heel to shin test

Sensory Ataxia If both side of posterior column of the spinal cord is lesioned the body position is completely lost and the patient obsereves accurately his steps during walking

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