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The somatic nervous system is that part of the peripheral nervous system associated with the voluntary control of body movements through the action of skeletal muscles, and also reception of external stimuli. The somatic nervous system consists of afferent fibers that receive information from external sources, and efferent fibers that are responsible for muscle contraction.
The basic route of the efferent somatic nervous system includes a two neuron sequence. The first is the upper motor neuron, whose cell body is located in the precentral gyrus (Brodman Area 4) of the brain. It receives stimuli from this area to control skeletal (voluntary) muscle. The upper motor neuron carries this stimulus down the cortico spinal tract and synapses in the ventral horn of the spinal cord with the lower motor neuron. The upper motor neuron releases acetylcholine from its axon terminal knobs and these are received by nicotinic receptors on the lower motor neuron. The lower motor neurons cell body sends the stimulus down its axon via the ventral root of the spinal cord and proceeds to its neuromuscular junction of its skeletal muscle. There, it releases acetylcholine from its axon terminal knobs to the muscles nicotinic receptors, resulting in stimulus to contract the muscle.
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Nervous system Brain - Spinal cord - Central nervous system - Peripheral nervous system - Somatic nervous system - Autonomic nervous system - Sympathetic nervous system - Parasympathetic nervous system
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