The somatic nervous system (SNS) is the part of the peripheral nervous system responsible for our conscious perception of the environment through general and special senses as well as for our voluntary motor responses to that perception by means of skeletal muscles. In this chapter, you will look at the peripheral sensory structures that receive input from environmental stimuli, how the information is integrated in the CNS and at the motor neurons of the CNS that react to those stimuli sending motor responses to skeletal muscles.
- 13.1: Introduction to the Somatic Nervous System
- The distinction between the structures (i.e., anatomy) of the peripheral and central nervous systems and functions (i.e., physiology) of the somatic and autonomic systems can most easily be demonstrated through a simple reflex action. When you touch a hot stove, you pull your hand away. Sensory receptors in the skin sense extreme temperature and the early signs of tissue damage. This triggers an action potential, which travels along the sensory fiber from the skin.
- 13.2: Somatic Senses: General and Special Senses
- A major role of sensory receptors is to help us learn about the environment around us, or about the state of our internal environment. Stimuli from varying sources, and of different types, are received and changed into the electrochemical signals of the nervous system. This occurs when a stimulus changes the cell membrane potential of a sensory neuron. The stimulus causes the sensory cell to produce an action potential that is relayed into the central nervous system (CNS).
- 13.3: Integration of Somatic Functions
- Specific regions of the CNS coordinate different somatic processes using sensory inputs and motor outputs of peripheral nerves. A simple case is a reflex caused by a synapse between a dorsal sensory neuron axon and a motor neuron in the ventral horn. More complex arrangements are possible to integrate peripheral sensory information with higher processes.
- 13.4: Somatic Motor Responses
- The defining characteristic of the somatic nervous system is that it controls skeletal muscles. Somatic senses inform the nervous system about the external environment, but the response to that is through voluntary muscle movement. The term “voluntary” suggests that there is a conscious decision to make a movement. However, some aspects of the somatic system use voluntary muscles without conscious control.