Neurons - • Tension on muscle spindle • Excitation of...

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Neurons in the spinal cord involved in motor function Two types of anterior horn motoneurons: o Alpha motor neurons: axonal size 9-20 microns (a nerve fiber), innervates skeletal muscle fibers (extrafusal fibers) – motor unit o Gamma motor neurons: axonal size 5 microns (a fibers), innervates intrafusal fibers containing muscle spindles Interneurons: o 30 times more interneurons than anterior horn cells o Integrative functions o Most of the incoming motor cortex (and sensory) signals are transmitted to interneurons Gamma motor system: an excitatory pathway due to co-activation of alpha and gamma motor neurons; a local positive feedback system; pyramidal tract usually excites both alpha and gamma motor neurons Sequence: Excitation of gamma motor neurons Contraction of intrafusal fibers
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Unformatted text preview: • Tension on muscle spindle • Excitation of dorsal root ganglion neuron • Excitatory synapse with alpha motor neuron • Contraction o extrafusal fibers o Increased muscle tension Golgi tendon organ (GTO) system: an inhibitory pathway; a local negative feedback system Sequence: • Contraction of extrafusal fibers • Increased tension on GTO • Excitation of DRG neuron • Excitation of inhibitory interneuron • Inhibition of alpha motor neurons • Decreased muscle tension Babinski reflex: an abnormal response due to the blockage of cortical signals to spinal inhibitory neuron; dorsiflexion of the big toe in response to scratching the sole of the foot (weird); indicates lesion of the corticospinal tract...
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