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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- all other (indirect) pathways
Fig. 12-1 Ganong
convert thoughts into actionsBasal Ganglia
The substantia nigra of midbrain sends dopaminergic neurons to the basal ganglia.
stimulatory at D1 receptors, inhibitory at D2 receptors
Basal ganglia send out GABA-ergic neurons to each other and to the thalamus.Inhibitory Neurotransmitters
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.
rigidity and involuntary tremor
decreased dopamine from substantia nigra
difficulty in initiating movement because all muscles stimulatedTwo Diseases
not corticospinal, therefore can also be considered extrapyramidal
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 organizationBrain Stem Functions
Autonomic vs. Somatic Motor Pathways extrapyramidal