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Cerebellum

Cerebellum. coordination of muscle activity, especially during movement when directly stimulated, causes little or no sensation or movement cerebellar dysfunction characterized by lack of coordination (= ataxia) general: “drunken” movements slurred speech specific: dysmetria

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Cerebellum

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  1. Cerebellum • coordination of muscle activity, especially during movement • when directly stimulated, causes little or no sensation or movement • cerebellar dysfunction characterized by lack of coordination (= ataxia) • general: • “drunken” movements • slurred speech • specific: • dysmetria • past pointing, bumping into objects • intention tremor • The cerebellum normally smooths out movements. Fig. 14.1

  2. Extrapyramidal Systems • Anatomically speaking, there is no “extrapyramidal system.” • In clinical usage, extrapyramidal most often refers to functions of the basal ganglia.

  3. pyramidal (direct) pathways extrapyramidal - all other (indirect) pathways and thalamus Fig. 12-1 Ganong

  4. execute motor programs, set the sequence for complex movements convert thoughts into actions Basal Ganglia Fig. 14.16

  5. two inhibitory neurotransmitters involved dopamine The substantia nigra of midbrain sends dopaminergic neurons to the basal ganglia. stimulatory at D1 receptors, inhibitory at D2 receptors GABA Basal ganglia send out GABA-ergic neurons to each other and to the thalamus. Inhibitory Neurotransmitters Fig. 12-9 Ganong Fig. 12-8 Ganong

  6. Huntington Disease (Huntington’s Chorea) hyperkinetic, involuntary movements Degeneration of GABA-ergic neurons leads to decreased inhibition of movement. Basal ganglia motor programs triggered, without being controlled by conscious thought. Parkinson Disease rigidity and involuntary tremor decreased dopamine from substantia nigra difficulty in initiating movement because all muscles stimulated Two Diseases

  7. not corticospinal, therefore can also be considered extrapyramidal antigravity responses axial/proximal muscles medial motor system e.g., medial reticulospinal tracts posture: oppose gravity when there is no movement general stimulation of muscle tone (axial muscles, extensors) via stimulation of A motor neurons e.g., vestibulospinal tracts movement: righting reflex when tripped e.g., walking: midbrain and spinal cord organization Brain Stem Functions Fig. 13.4

  8. Somatic and Visceral (Autonomic) Reflexes • Reflex arcs are similar in both the somatic and visceral pathways. Fawcett, Histology

  9. Autonomic vs. Somatic Motor Pathways • The most significant differences are on the efferent limb of the neural arc. • somatic • one motor neuron from CNS to effector tissue • effector tissue: skeletal muscle • autonomic • two motor neurons from CNS to effector tissue • pre- and postganglionic neurons • effector tissues: smooth muscle, cardiac muscle and glands Fig. 15.2

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