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Subcortical Motor Systems: Cerebellum

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Subcortical Motor Systems: Cerebellum NN 23 Outline Anatomy Subcortical Motor Cerebellar cortex Neuronal circuitry Systems: cerebellum Cerebellar connections 陽明大學醫學院 腦科所 Vestibulocerebellum Spinocerebellum 陳昌明 副教授 Neocerebellum Other cerebellar functions Motor Loops Pyramidal Tract and Associated Circuits Cortex ---> Subcortex ---> Cortex ---> Spinal cord upper motor neuron UMN Cerebellum coordination of movement Cerebellum BASAL Basal Ganglia GANGLIA pyramidal tract selection & initiation of voluntary movements ~ lower motor neuron UMN Cerebellar functions Cerebellum: Anatomy The main functions: Coordinating skilled voluntary movements by influencing muscle activity, Controlling equilibrium and muscle tone through connections with the vestibular system and the spinal cord and its gamma motor neurons. 1. Found in the posterior Cranial fossa 2. Forms a roof over the 4th ventricle 3. Lies above and behind the medullar and pons 1 NN 23 Cerebellum: Anatomy Cerebellum: External features Folia & lobules Longitudinal division analogous to gyrus Vermis, Paravermal Vermis - along midline Region, Cerebellar Hemisphere output ---> ventromedial pathway Transverse division Hemispheres Anterior Lobe Posterior Lobe output ---> lateral pathway Flocculonodular Deep cerebellar nuclei Lobe fastigial, interposed, & dentate Major output structures ~ Functional divisions of cerebellar cortex Lobes Superior surface External Features Two deep fissures Primary fissure Posterosuperior fissure Three lobs Flocculonodular lobe 絨球小結葉 flocculus and nodule Anterior lobe Corpus of cerebellar Posterior lobe Tonsil of cerebellum 小腦扁桃体 On inferior surface of hemispheral portion just nearby foramen magnum IICP tonsilar herniation View from below 2 NN 23 Lobes & Lobules Subdivision of lobes Subdivision of lobes Three peduncles Inferior cerebellar peduncle 下小腦脚 － connect with medulla and with spinal cord, contain both afferent and efferent fibers Middle cerebellar peduncle 中小腦脚－ connect with pons, contain afferent fibers Superior cerebellar peduncle 上小腦脚－ connect with midbrain, contain mostly efferent fibers Deep Cerebellar Nuclei Blood supply Deep Cerebellar Nuclei: Dentate Interposed Fastigial 3 NN 23 Internal structures Internal structures Gray matter Cerebellar cortex Fastigial nucleus Cerebellar cortex Globose nucleus Cerebellar nuclei Dentate nucleus Emboliform nucleus Dentate nucleus 齒狀核 Fastigial nucleus 頂核 Interposed nucleus 中間核 Emboliform nucleus 栓狀核 medullary center Globose nucleus 球狀核 White matter－medullary center 髓体 髓体 Medullary center Cerebellum: 3 layered cortex Molecular layer parallel fibers • axons of granule cells • runs parallel to long axis of folium dendrites of Purkinje cells Purkinge cell layer Large somas Send axons to underlying white matter perpendicular to main axis of folium ~ Cerebellum: 3 layered cortex Granular layer innermost layer small, densely packed granule cells > # neurons in cerebral cortex ~ 4 NN 23 Cerebellar Cortex Cerebellum: 3 layered cortex 3 layers, 2 kinds of input fibers, 5 types of neurons Inputs Molecular • Climbing fibers •only from Inferior olive • Mossy fibers Purkinje Output • Purkinje neurons Interneurons • Granule neurons Molecular Granule • Purkinje Stellate neurons Granular • Basket neurons • Golgi neurons Climbing fibers Mossy fibers 10% of the brain’s volume, & >50% of the total number of neurons in the brain Intrinsic pathways & cells Mossy fiber inputs to the cerebellum convey the sensory information used to evaluate the overall sensory context of the movement The climbing fibers may convey information about movement errors Inhibitory interneurons Cerebellum: Internal configurations Cerebellar Cortex : I. Molecular Layer The Golgi cell is found among the granule cells. • Two types of interneurons • Stellate Cell --- taurine (inhibitory) The stellate and basket cells live in afferent: parallel fiber the molecular layer. efferent: Purkinje cell dendrite • Basket Cell ---- GABA (inhibitory) The basket cell drops axon afferent: parallel fiber branches down into the Purkinje efferent: Purkinje cell soma cell layer where the branches wrap • Two types of fibers around the cell bodies like baskets. • Parallel Fiber granule cell axon • Purkinje Cell Dendrite 5 NN 23 Cerebellum: Internal configurations Cerebellum: Internal configurations Cerebellar Cortex : II. Purkinje Cell Layer Cerebellar Cortex : III. Granular Layer Purkinje Cell Granule Cell 15,000,000 in number 50,000,000,000 in number GABA (inhibitory) glutamic acid (excitatory) Afferent from: afferent: mossy fiber parallel fiber efferent: Purkinje cell dendrite, basket cell, climbing fiber stellate cell stellate cell, Golgi cell basket cell Golgi Cell Efferent to: deep cortical nuclei GABA (inhibitory) Bergman’s glial cell afferent: parallel fiber, mossy fiber rosette efferent: granule cell dendrite Cerebellum: Internal configurations Mossy fibers Synaptic Glomerulus : Afferent Originate in the pontine nuclei, the spinal terminals on granular layer cord, the brainstem reticular formation, Mossy Fiber Rosette and the vestibular nuclei • Afferent fibers except inferior olivary input Make excitatory projections onto the • 2/3 of medullary center cerebellar nuclei and onto granule cells in the cerebellar cortex. Granule Cell Dendrite • main afferent input Each mossy fiber innervates hundreds of granule cells Golgi Cell Axon • synapse on granule cell dendrite • GABA (inhibitory) • Surrounded by Astrocyte Foot Process Mossy fibers The climbing fiber A mossy fiber has an axon Originate exclusively in the inferior terminal that ends in a large, bulbous swelling. olive and make excitatory projections Enter the granule cell layer and onto the cerebellar nuclei and onto synapse on the dendrites of the Purkinje cells. granule cells Each climbing fiber associates with The granule cells reach out with little "claws" to grasp the terminals. only one Purkinje cell, and each The granule cells then send their climbing fiber only goes to one to axons up to the molecular layer, where they end in a T and run three Purkinje cells. parallel to the surface, thus called parallel fibers. 6 NN 23 Role of climbing fibers Connectivity of Cerebellar Intimate connections between the neurons Cortex of the inferior olivary nucleus and the Purkinje cells. The inferior olivary may be an error detector When a particular action goes off target, inferior olivary nucleus neurons are activated. This results in powerful activation of the target Purkinje cells through the climbing fibers. Activation of Purkinje cells inhibits the deep cerebellar nucleus neurons, terminating the unwanted component of the action Cerebellum Classifications Developmental History of Cerebellum • Classification by Phylogenetic and Ontogenic Development Archicerebellum Paleocerebllum Neocerebellum • Classification by Afferent Connection Vestibulocerebellum Spinocerebellum Pontocerebellum • Classification by Efferent Connection Vermis Paravermal Region Cerebellar Hemisphere Three functional divisions Cerebellar divisions Vestibulocerebellum Spinocerebellum: 前庭小腦 Vermis Spinocerebellum Intermediate hem. Archicerebellum 原小腦 (Vermis + Intermed. Hem) Cerebrocerebellum: Flocculonodular lobe Lateral hem. Intermediate zone Intermediate Vermis Control of limbs Spinocerebellum Lateral zone and trunk 脊髓小腦 Cerebrocerebellum Paleocerebellum 舊小腦 (Lateral hemisphere) Planning of movement+ Vermis and Vermis intermediate zone IVth vent Vestibulo-cerebellum Intermediate hem. Cerebrocerebellum (Floculo-nodular lobe) Lateral hem. 大腦小腦 Flocculonodular lobe Control of eye & Neocerebellum 新小腦 head movements Balance Lateral zone NTA Fig. 13-1 Floculo-nodular lobe 7 NN 23 Responds to vestibular stimuli Vestibulocerebellum Vestibulo- from internal ear cerebellum assists in maintaining Comprises the flocculonodular lobe and its equilibrium by modification in connections with the vestibular nuclei. muscle tone postural muscles Phylogenetically the oldest of cerebellum. □eye muscles Involved in vestibular reflexes (such as the □trapezius vestibuloocular reflex) and in postural □sternomastoid maintenance. □erector spinae An important regulator of the vestibular Main deciding factor: fastigial system. nucleus Damage to this region will result in vertigo Which deep nucleus controls and nystagmus equilibrium: fastigial nucles Vestibulocerebellum (floculonodular lobe) Vestibulo-cerebellar connections Connections Afferents: input from ipsilateral vestibular nuclei The flocculonodular lobe and primary vestibular nerve receives input from the vestibular nerve & from Efferents: to bilat vestibular nucleus → the vestibular nuclei. (1) vestibulospinal tract → motor neurons of anterior horn for reflexively control of equilibrium Some of the Purkinje cells (2) vestibulo-ocular tract → medial longitudinal here may leave the fasciculus → CN nucleus 3, 4, 6 for EOM control. cerebellum to synapse in • Function: involved in eye movements and maintain bilateral vestibular nuclei balance (the only exception to the Efferents: to reticular formation → rule of Purkinje projection (1) Cerebello-reticular tract → reticular nucleus in to deep cerebellar nuclei) brain stem → reticulospinal tract → motor neurons of anterior horn for reflexively control of equilibrium MiMain CConnections i of fh the Spinocerebellum Vestibulocerebellum (vemis and intermediate) Vestibular Organ Floculonodular Lobe Vermis VESTIBULAR NUCLEUS vestibulospinal tract MLF FASTIGIAL NUCLEUS lower motor neuron
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