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Chapter 9 The Cerebellum: Ataxia Cerebellum: Functions: Influences the timing and force of contractions of voluntary muscles Makes movements coordinated and smooth “3” is the key number with the cerebellum: 3 parts (divided sagittally) 3 lobes (divided horizontally) 3 peduncles 3 layers of cortex 3 output nuclei 3 clinical syndromes Fig. 5-1 Subdivisions of the cerebellum: (2nd oldest) (newest) (oldest) (superior surface of cerebellum) (paravermal) superior surface of cerebellum: (inferior surface of cerebellum) inferior surface of cerebellum: cerebellar tonsils folia tonsil the folia sharing a common stem of white matter form a lobule tonsillar herniation: cerebellar tumor hematoma Chiari malformation superior: mostly output transverse middle: all input motor cortex inferior: mostly input dorsal ,etc. Arbor vitae (tree of life) Gray matter (cerebellar cortex) white matter Gray matter layers: external molecular Purkinje granular internal Gray matter White matter Fig. 9-5 (all other afferents) (from inf. olivary nucleus) Climbing fibers excite Purkinje neurons and cerebellar nuclei Mossy fibers excite granule neurons and cerebellar nuclei Granule cells (the only excitatory neuron of the cerebellar cortex) excite: Purkinje neurons stellate neurons inhibit Purkinje neurons basket neurons inhibit Purkinje neurons Golgi neurons inhibit granule cells Purkinje neurons (the only output neuron of the cerebellar cortex) inhibit: all the cerebellar nuclei (to regulate the output fibers of the cerebellum) •excited by climbing and mossy fibers •inhibited by Purkinje cells Fig. 9-4 (transverse section at pontomedullary junction) vermis & fastigial nuclei: control head, trunk, proximal limb movements bilaterally hemispheres & the interposed and dentate nuclei: control progressively more distal limb movements ipsilaterally Fig. 9-7 Posterior lobe (lateral cerebellar hemispheres): are concerned with learning and storage of all the sequential components of skilled movements input: (corticopontocerebellar) from association areas of cerebral cortex where desire to perform volitional movements occurs output: to motor cortex where skilled movements are represented Posterior lobe circuitry: Left cerebral cortex (assoc.areas) internal capsule cerebral crus ipsilateral pontine nuclei pontine nuclei mossy fibers transverse pontine fibers Input Fig. 9-8 transverse pontine fibers (decussate) middle cerebellar peduncle Right posterior lobe L motor cortex VL thalamus thru contralat. red nucleus (decussation) superior cerebellar peduncle superior cerebellar peduncle dentate nucleus Output Fig. 9-8 R posterior lobe Purkinje neurons Posterior lobe is commonly affected by CVA’s, tumors, trauma, and degenerative diseases Fig. 5-1 Posterior lobe syndrome: intention tremors (volitional) ataxia decreased muscle tone dysmetria dysdiadochokinesia dysarthria rebound phenomenon *unilateral lesion ipsilateral symptoms Fig. 9-10 Anterior lobe (vermal and paravermal parts): input: sensory information from muscular, joint, and cutaneous mechanoreceptors output: to limbs (to maintain coordination of limb movements while skilled movements are being executed) - lower limbs are represented anteriorly - upper limbs and head are represented posteriorly Anterior lobe circuitry: Fig. 9-12 anterior part of ipsilateral anterior lobe inferior cerebellar peduncle dorsal spinocerebellar tract dorsal nucleus of Clarke (C8-L2) gracile tract muscle spindles, GTO’s, cutaneous receptors of the lower limbs dorsal nucleus lower limb input Fig. 2-4 Anterior lobe circuitry: posterior part of ipsilat. anterior lobe Fig. 9-12 cuneocerebellar tract inferior cerebellar peduncle cuneocerebellar tract accessory cuneate nucleus cuneate tract muscle spindles, GTO’s, cutaneous receptors of upper limbs upper limb input Ventral spinocerebellar tract: originates from neurons in intermediate zone and anterior horn (at lumbar levels) carries information about ongoing influences of descending motor pathways on the spinal gray matter decussates twice (in cord and in superior cerebellar peduncle) arrives in anterior lobe Anterior lobe circuitry: fastigial globose emboliform Output vermis fastigial and vestibular nuclei and RF bilateral influence on head, neck, and proximal limb muscles paravermis interposed nuclei contralateral red nucleus and RF distal limb muscles Fig. 9-12 Anterior lobe is commonly affected by chronic alcoholism (malnutrion degeneration of Purkinje neurons) Fig. 5-1 Anterior lobe syndrome: gait instability walk as if drunk stagger stiff-legged difficulty with heel-shin test gait ataxia Fig. 9-14 Flocculonodular lobe: responsible for the coordination of the muscles associated with equilibrium and eye movements Flocculonodular lobe circuitry: Input and Output vestibulo-ocular projections external ocular muscles med. vestibulospinal tract bilateral axial muscles vestibular nuclei and reticular formation fastigial nucei flocculonodular lobe vestibular nuclei inferior cerebellar peduncle direct and indirect vestibulocerebellar fibers vestibular apparatus (inner ear) 41 Fig. 9-15 Flocculonodular lobe is commonly affected by tumors (ie. medulloblastomas) in the roof of the 4th ventricle Fig. 5-1 Flocculonodular lobe syndrome: truncal ataxia Fig. 9-16 lack of coordination of paraxial muscles reel and sway from side to side Chapter 9 Review know the three parts of the cerebellum (when divided sagitally) know the three cerebellar lobes and the fissures that separate them know the major sources of input into the three lobes of the cerebellum know the portions of the brainstem each cerebellar peduncle connects to know the primary type of fiber in the cerebellar peduncles know the layers of the cerebellar cortex and the cells found in them know the two ways the cerebellar cortex and cerebral cortex differ know the circuitry (excitatory and inhibitory connections) of the cerebellar cortex know the effects of the connections of the climbing and mossy on the cerebellar nuclei and the cells of the cerebellar cortex know the cerebellar nuclei and their relationships to each other know the portions of the cerebellar cortex that project to the cerebellar nuclei and the movements they control know the main functions of the three lobes of the cerebellum know the connections of the three lobes of the cerebellum know the signs and symptoms associated with the three cerebellar syndromes