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Psych_115_-_Motor_Systems

Psych_115_-_Motor_Systems - PRINCIPLES OF BEHAVIORAL...

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PRINCIPLES OF BEHAVIORAL NEUROSCIENCE Motor Systems May 12, 2011
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Neuromuscular Junction Neuron within the ventral horn of the spinal cord (called an alpha motoneuron) sends an axon to a structure on the muscle called the motor end plate. That connection is the neuromuscular junction. The alpha-motoneuron gets lots of inputs from other neurons and when it is activated, it releases acetylcholine onto the motor endplate. ACh depolarizes muscle cells, causes an action potential and triggers muscle contraction (blocked by poison dart frog).
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Stretch Reflex There must be a mechanism for sensing how contracted or stretched a muscle is and turning off the contraction when an appropriate level is reached. This involves structures called the muscle spindle and the golgi tendon organ.
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Muscle Spindle Involves a primary afferent fiber (nerve ending that connects to spinal cord). The afferent fiber wraps around the nuclear bag. When the muscle is stretched, so is the nuclear bag. Therefore, you get an activation of the afferent fibers which transmits information to the spinal cord about that stretch. This contributes to the sense of proprioception.
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Stretch Reflex When a muscle is stretched, this change is sensed by the muscle spindle and the primary spindle afferent fibers are activated. The DRG neuron that transmits this input to the spinal cord, synapses onto a motoneuron and can trigger contraction of the appropriate muscle fibers to oppose the stretch. It also inhibits the opponent motoneuron via an inhibitory interneuron.
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