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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 Inhibitory interneurons Intrinsic pathways & cells The Golgi cell is found among the granule cells. The stellate and basket cells live in the molecular layer. The basket cell drops axon branches down into the Purkinje cell layer where the branches wrap around the cell bodies like baskets. Cerebellum: Internal configurations Cerebellum: Internal configurations Cerebellar Cortex : I. Molecular Layer Cerebellar Cortex : II. Purkinje Cell Layer Purkinje Cell • Two types of interneurons • Stellate Cell --- taurine (inhibitory) 15,000,000 in number afferent: parallel fiber GABA (inhibitory) efferent: Purkinje cell dendrite • Afferent from: Basket Cell ---- GABA (inhibitory) parallel fiber afferent: parallel fiber efferent: Purkinje cell soma climbing fiber stellate cell • Two types of fibers basket cell • Parallel Fiber Efferent to: deep cortical nuclei granule cell axon Bergman’s glial cell • Purkinje Cell Dendrite 5 NN 23 Cerebellum: Internal configurations Cerebellum: Internal configurations Synaptic Glomerulus : Afferent Cerebellar Cortex : III. Granular Layer terminals on granular layer Granule Cell Mossy Fiber Rosette 50,000,000,000 in number • Afferent fibers except inferior olivary glutamic acid (excitatory) input afferent: mossy fiber • 2/3 of medullary center efferent: Purkinje cell dendrite, basket cell, Granule Cell Dendrite stellate cell, Golgi cell • main afferent input Golgi Cell Golgi Cell Axon GABA (inhibitory) • synapse on granule cell dendrite afferent: parallel fiber, mossy fiber rosette • GABA (inhibitory) efferent: granule cell dendrite • Surrounded by Astrocyte Mossy fibers Mossy fibers Originate in the pontine nuclei, the spinal A mossy fiber has an axon cord, the brainstem reticular formation, terminal that ends in a large, and the vestibular nuclei bulbous swelling. Enter the granule cell layer and Make excitatory projections onto the synapse on the dendrites of cerebellar nuclei and onto granule cells in granule cells the cerebellar cortex. The granule cells reach out with little Each mossy fiber innervates hundreds of "claws" to grasp the terminals. granule cells The granule cells then send their axons up to the molecular layer, where they end in a T and run parallel to the surface, thus called parallel fibers. The climbing fiber Role of climbing fibers Originate exclusively in the inferior Intimate connections between the neurons olive and make excitatory projections of the inferior olivary nucleus and the onto the cerebellar nuclei and onto Purkinje cells. the Purkinje cells. The inferior olivary may be an error detector When a particular action goes off target, inferior Each climbing fiber associates with olivary nucleus neurons are activated. only one Purkinje cell, and each This results in powerful activation of the target climbing fiber only goes to one to Purkinje cells through the climbing fibers. three Purkinje cells. Activation of Purkinje cells inhibits the deep cerebellar nucleus neurons, terminating the unwanted component of the action 6 NN 23 Cerebellum Classifications Connectivity of Cerebellar Cortex • 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 Developmental History of Cerebellum Three functional divisions Vestibulocerebellum 前庭小腦 Archicerebellum 原小腦 Flocculonodular lobe Intermediate zone Intermediate Vermis Spinocerebellum Lateral zone 脊髓小腦 Paleocerebellum 舊小腦 Vermis and intermediate zone Cerebrocerebellum 大腦小腦 Flocculonodular lobe Neocerebellum 新小腦 Lateral zone Cerebellar divisions Vestibulocerebellum Spinocerebellum: Vermis Comprises the flocculonodular lobe and its Spinocerebellum Intermediate hem. (Vermis + Intermed. Hem) Cerebrocerebellum: connections with the vestibular nuclei. Control of limbs Lateral hem. Phylogenetically the oldest of cerebellum. and trunk Cerebrocerebellum Involved in vestibular reflexes (such as the (Lateral hemisphere) vestibuloocular reflex) and in postural Planning of movement+ Vermis maintenance. IVth vent Vestibulo-cerebellum Intermediate hem. An important regulator of the vestibular (Floculo-nodular lobe) Lateral hem. Control of eye & system. head movements Balance Damage to this region will result in vertigo and nystagmus NTA Fig. 13-1 Floculo-nodular lobe 7 NN 23 Vestibulo- Responds to vestibular stimuli Vestibulocerebellum from internal ear (floculonodular lobe) cerebellum assists in maintaining Connections equilibrium by modification in Afferents: input from ipsilateral vestibular nuclei muscle tone and primary vestibular nerve postural muscles Efferents: to bilat vestibular nucleus → □eye muscles (1) vestibulospinal tract → motor neurons of anterior □trapezius horn for reflexively control of equilibrium □sternomastoid (2) vestibulo-ocular tract → medial longitudinal → □erector spinae fasciculus CN nucleus 3, 4, 6 for EOM control. • Function: involved in eye movements and maintain Main deciding factor: fastigial balance nucleus Efferents: to reticular formation → Which deep nucleus controls → equilibrium: fastigial nucles (1) Cerebello-reticular tract reticular nucleus in brain stem → reticulospinal tract → motor neurons of anterior horn for reflexively control of equilibrium MiMain CConnections i of fh the Vestibulo-cerebellar connections Vestibulocerebellum The flocculonodular lobe Vestibular receives input from the Organ Floculonodular vestibular nerve & from Lobe Vermis the vestibular nuclei. VESTIBULAR NUCLEUS Some of the Purkinje cells here may leave the vestibulospinal tract cerebellum to synapse in bilateral vestibular nuclei MLF FASTIGIAL NUCLEUS (the only exception to the rule of Purkinje projection to deep cerebellar nuclei) lower motor neuron ARCHICEREBELLUM LMN Spinocerebellum (vemis and intermediate) Spinocerebellum The vermis & the intermediate zones of the cerebellar cortex, which connect to the fastigial & interposed nuclei, respectively. Extensive input from the spinal cord. Output projects to rubrospinal, vestibulospinal, and reticulospinal tracts Integration
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