Somatic Nervous System

The Somatic Nervous System is one of the three Subsystems groups of the Peripheral Nervous System that is largely associated with the voluntary control of body movements using the Skeletal Muscles. The other two are Autonomic and Enteric Systems.

Overall, the Nervous System is divided into Peripheral Nervous System and Central Nervous System.

The Somatic Nervous System is a system that involves afferent nerves or sensory nerves, and efferent nerves or motor nerves.

1.)  Afferent Nerves are responsible for allowing (relaying) sensation from the body to the Central Nervous System (CNS).

2.)  Efferent Nerves are responsible for sending out orders or commands from the Central Nervous System to the body. This stimulates a muscle contraction and includes all the neurons that are non-sensory that are connected with the Skeletal Muscle and the skin.


There are 43 Segments of Nerves in the Human Body. With each segment – there is a pair of sensory nerves and motor nerves.

In the body – 31 Segments of Nerves are in the Spinal Cord and 12 are in the Brain Stem.

Additionally – there are thousands of Association Nerves in the body.

Somatic Nervous System Consists of Two parts

1.)  Spinal Nerves

–  Spinal nerves are classified as peripheral nerves that carry sensory information into the spine and motor commands out of the spinal cord.

2.)  Cranial Nerves

–  Cranial Nerves are classified as nerve fibers that carry information into the brain stem and out of the brain stem.

–  They include smell, vision, eye, eye muscles, mouth, taste, ear, neck, shoulders, and tongue.


1.)  Controls all Voluntary muscular systems of the body

2.)  Control the process of Voluntary Reflex arcs

Nerve Signal Route

Within the efferent somatic nervous system – there is a sequence that begins in the upper cell bodies of motor neurons. This starts within the precentral gyrus and the stimuli are transmitted down the corticospinal tract via axons to control skeletal muscles (voluntary). The stimuli cross synapses of the brainstem and spinal cord.

Acetylcholine is released and received by postsynaptic receptors of muscles causing the stimulus to contract muscles.

Reflex Arcs

This a neural circuit that creates a link between a sensory input and a specific motor output. They can be different depending on the area and some are more complex than others.