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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
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


Extrapyramidal systems
Extrapyramidal Systems

  • Anatomically speaking, there is no “extrapyramidal system.”

  • In clinical usage, extrapyramidal most often refers to functions of the basal ganglia.


pyramidal

(direct)

pathways

extrapyramidal

- all other (indirect) pathways

and thalamus

Fig. 12-1 Ganong


Basal ganglia

execute motor programs, set the sequence for complex movements

convert thoughts into actions

Basal Ganglia

Fig. 14.16


Inhibitory neurotransmitters

two inhibitory neurotransmitters involved movements

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


Two diseases

Huntington Disease (Huntington’s Chorea) movements

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


Brain stem functions

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


Somatic and visceral autonomic reflexes
Somatic and Visceral (Autonomic) Reflexes extrapyramidal

  • Reflex arcs are similar in both the somatic and visceral pathways.

Fawcett,

Histology


Autonomic vs. Somatic Motor Pathways extrapyramidal

  • 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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