Neural Control of Muscle Fiber Contraction
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Each individual skeletal
muscle cell or fiber is controlled by a motor neuron (nerve
cell). A process of the neuron, the axon, reaches the muscle
fiber and forms a connection called the neuromuscular junction. At
the neuromuscular junction the axons branches and the tips of these
branches expand into what are called synaptic end bulbs or synaptic
knobs. Within the synaptic end bulbs there are synaptic
vesicles that contain the neurotransmitter acetylcholine
(ACh). |
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The motor neuron initiates a
contraction when an electrical impulse travels along the axon and
reaches the synaptic end bulb. The impulse arriving at the synaptic
end bulb causes the synaptic vesicles to fuse with the neuron's cell
membrane and release ACh into a space between the neuron cell
membrane and the sarcolemma called the synaptic cleft. ACh
diffuses across the synaptic cleft to the motor end plate, a
part of the sarcolemma that is highly folded and contains receptor
molecules for ACh. |
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The binding of ACh to its
receptors on the motor end plate triggers an electrical impulse
called an action potential, that sweeps along the sarcolemma
and T- tubules. Neural stimulation ends when the enzyme in
the synaptic cleft, acetylcholinesterase, breaks down the
ACh.
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