cerebellum by dr.arshad
TRANSCRIPT
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CEREBELLUM
Functional anatomy
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Location of cerebellum:
• Largest part of hindbrain• Occupies most of posterior cranial fossa• Lies behind pons & medulla– forming roof of 4th ventricle
• Separated from posterior part of cerebrum– by tentorium cerebelli
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Important facts
• The hemispheres, vermis, flocculus, nodule, and tonsil are major landmarks of the cerebellar cortex.
• Afferent fibers end in the three-layered cerebellar cortex. The Purkinje cells have axons that end in the cerebellar nuclei.
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• Motor part of the brain, serving to maintain equilibrium and coordinate muscle contractions.
• Makes a special contribution to synergy of muscle action (i.e., to the synchronized contractions and relaxations of different muscles that make up a useful movement).
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• Ensures that contraction of the proper muscles occurs at the appropriate time, each with the correct force.
• Participates in learning patterns of neuronal activity needed for carrying out movements and in the execution of the encoded instructions.
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• Imagined movements are accompanied by an increase in cerebellar blood flow that is larger than the increase detected in the motor areas of the cerebral cortex.
• Evidence also suggests that the cerebellum has sensory and cognitive functions.
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• The cerebellum consists of a cortex, or surface layer, of gray matter contained in transverse folds or folia plus a central body of white matter.
• Four pairs of central nuclei are embedded in the cerebellar white matter.
• Three pairs of cerebellar peduncles, composed of myelinated axons, connect the cerebellum with the brain stem.
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Cerebral peduncles:
• Joined to the brain stem via:• Superior cerebellar peduncle –> Midbrain• Middle cerebellar peduncle –> Pons• Inferior cerebellar peduncle –> Medulla
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Major contents of the cerebellar peduncles. For simplicity, the inferior cerebellar peduncle is depicted
as containing only climbing fibers
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Contents of Cerebellar Peduncles
• The superior cerebellar peduncle contains cerebellar efferent fibers, the ventral spinocerebellar tract, and tectocerebellar fibers.
• The middle cerebellar peduncle consists of fibers from the contralateral pontine nuclei
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Contents of Cerebellar Peduncles
• Inferior cerebellar peduncle contains olivocerebellar and dorsal spinocerebellar fibers and the vestibulocerebellar and fastigiobulbar connections.
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Microstructure
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Microscopic structure of cerebellar cortex (3 layers
• External Molecular layer• Middle Purkinje layer– large flask shaped neurons– arranged in single tier in a plane transverse to
folium– dendrites produce profuse branching– receive communications afferent fibres entering
cerebellum
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– axons run to DEEP CEREBELLAR NUCLEI• sole output of cerebellar cortex
– functionally• inhibitory (GABA)–Stimulate Purkinje cells, inhibits deep nuclei
• Internal Granular layer– closely packed small neurons
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All afferent input via 2 different fibres
• Mossy fibres– entire inflow of cerebellum• except from inferior olive• particularly from cerebral cortex via pons
– they synapse in expanded MOSS-like appearance with granule & Golgi cells in granular layer
– fast-firing• rapid adjustment for ongoing movement
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• Climbing fibres– inflow from inferior olive– run up and synapse with dendrites of single
Purkinje cell– slow-firing• helps in learning muscle habits
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Origin of climbing fibers from the inferior olivary nucleus. The axon of each olivary neuron has several branches, each of which
forms the single climbing fiber of one Purkinje cell.
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• The fastigial, interposed, and dentate nuclei receive branches of all cerebellar afferent fibers and the output of the cortex.
• These nuclei contain the cerebellar efferent neurons.
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• The vestibular system is connected ipsilaterally with the vestibulocerebellum, which comprises the flocculonodular lobe and the fastigial nucleus.
• This nucleus projects to the ipsilateral vestibular nuclei and to the reticular formation
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• Proprioceptive signals are carried ipsilaterally to the spinocerebellum, which consists of vermis, paravermal zones, and interposed nuclei.
• These nuclei project to the contralateral red nucleus and to the posterior division of the contralateral ventrolateral (VLp) thalamic nucleus. The VLp projects to the primary motor cortex.
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Connections of vestibulocerebellum and vestibular nuclei. Afferents-blue; efferents-red;neurons-black
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Connections of spinocerebellum and vestibular nuclei. Afferents-blue; efferents-red;neurons-black
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Connections of pontocerebellum. Afferents-blue; efferents-red;neurons-black