Somatic nervous system

Somatic nervous system
1. (Brain) Precentral gyrus: the origin of nerve signals initiating movement. 2. (Cross Section of Spinal Cord) Corticospinal tract: Mediator of message from brain to skeletal muscles. 3. Axon: the messenger cell that carries the command to contract muscles. 4. Neuromuscular junction: the messenger axon cell tells muscle cells to contract at this intersection
Identifiers
FMA	9904
Anatomical terminology []

2. (Cross Section of Spinal Cord) Corticospinal tract: Mediator of message from brain to skeletal muscles.

3. Axon: the messenger cell that carries the command to contract muscles.

The somatic nervous system (SoNS or voluntary nervous system) is the part of the peripheral nervous system associated with skeletal muscle control of body movements. The SoNS consists of afferent nerves and efferent nerves. Afferent nerves are responsible for relaying sensation from the body to the central nervous system (CNS); efferent nerves are responsible for sending out commands from the CNS to the body, stimulating muscle contraction; they include all the non-sensory neurons connected with skeletal muscles and skin. The a- of afferent and the e- of efferent correspond to the prefixes ad- (to, toward) and ex- (out of).

There are 43 segments of nerves in the human body. With each segment, there is a pair of sensory and motor nerves. In the body, 31 segments of nerves are in the spinal cord and 12 are in the brain stem.

Besides these, thousands of association nerves are also present in the body.

Thus somatic nervous system consists of two parts:

The somatic nervous system controls all voluntary muscular systems within the body, and the process of involuntary reflex arcs.

The basic route of nerve signals within the efferent somatic nervous system involves a sequence that begins in the upper cell bodies of motor neurons (upper motor neurons) within the precentral gyrus (which approximates the primary motor cortex). Stimuli from the precentral gyrus are transmitted from upper motor neurons and down the corticospinal tract, via axons to control skeletal (voluntary) muscles. These stimuli are conveyed from upper motor neurons through the ventral horn of the spinal cord, and across synapses to be received by the sensory receptors of alpha motor neurons (large lower motor neurons) of the brainstem and spinal cord.