Nervous System, Somatic Health Article

Definition

The somatic nervous system (SNS) is a division of the peripheral nervous system (PNS). The SNS controls voluntary activities, such as movement of skeletal muscles. It includes both sensory and motor nerves. Sensory nerves convey nerve impulses from the sense organs to the central nervous system (CNS), while motor nerves convey nerve impulses from the CNS to skeletal muscle effectors.

Nervous tissue

All nervous tissue—including that of the SNS—consists of two main cell types: neurons and glial cells. Neurons transmit nerve signals and are surrounded by glial cells, that provide mechanical and physical support as well as electrical insulation between neurons.

Neurons

A neuron consists of a cell body, the soma, which contains the nucleus and surrounding cytoplasm, several short thread-like projections, called dendrites, and of one long filament, called the axon. The dendrites receive information from other nearby cells and transmit the signals to the soma and the axon carries signals away from the neuron. Both axons and dendrites are surrounded by a white protective coating called the myelin sheath. The average adult brain contains about 100 billion neurons. Neurons are also the longest cells of the body, a single axon can be several feet long. There are two types of neurons found in the SNS: sensory neurons, which typically have long dendrites and short axons, and carry messages from sensory receptors to the CNS, and motor neurons, which have a long axon and short dendrites and transmit signals from the CNS to muscles or glands.

The nervous system

The nervous system of the human body is divided into the central nervous system (CNS), consisting of the spinal cord and brain, and the peripheral nervous system (PNS), consisting of all the nerves that connect the CNS with organs, muscles, blood vessels and glands. The PNS is subdivided into the somatic nervous system (SNS) and the autonomic nervous system (ANS). The ANS is further divided by function into sympathetic and parasympathetic systems.