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Motor system

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Western University
Physiology 3120
Tom Stavraky

Human Physiology Wednesday, November 11, 2009 “Neuro IX” Motor System • Signal starts in cerebral cortex, which projects to the basal ganglia & the cerebellum • By the time the instruction is in motor cortex, it is well specified • Characteristics of motor control (efferent)  Hierarchical  Have serial pathways & parallel pathways • Once muscles contract, there is the possibility for afferent feedback  Can come back to (I) spinal cord (for spinal reflexes), (II) thalamus and somatosensory cortex, or (III) cerebellum • Types of muscle receptors 1. Muscle spindle (shape of spindle = fusiform) group Ia  Signals length & velocity of muscle stretch (i.e. vibration of triceps muscle or Achilles tendon)  In parallel with extrafusal muscle fibres (innervated by alpha-MN) 2. Muscle spindle group IIa  Signals length only  Not excited by a vibration  In parallel with extrafusal muscle fibres 3. Golgi tendon organs  Located at boundary between extrafusal muscle fibres & tendon  When EFMF contracts, it pulls on the Golgi tendon organs  Very sensitive to active tension during contraction • Muscle spindles  Contain muscle & a receptor associated with it  Afferent nerve (annulospiral sensory receptor) wraps around the fusiform shape  Innervated by a gamma motor neuron (efferent nerve) = fusimotor neuron  Innervates intrafusal muscle fibres  Intrafusa
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