Question

explain the concept of the somatic nervous system?

provide an example of how it works

Answer 1

Somatic Nervous System Definition

The somatic nervous system (SoNS), also known as the voluntary nervous system, is a part of the peripheral nervous system (PNS). It consists of neurons that are associated with skeletal or striated muscle fibers and influence voluntary movements of the body.

The peripheral nervous system is made up of all the neurons that exist outside the brain and spinal cord. It acts as an intermediary between the central nervous system (CNS) and muscles, skin and sensory organs. The nerves of the PNS send electrochemical signals back and forth between the CNS, and the rest of the body. A large part of the PNS is composed of 12 pairs of cranial nerves and 31 pairs of spinal nerves. Some of the neurons in these nerves have sensory function and others have a motor function. The motor neurons that innervate striated muscles form the somatic nervous system.

Functions of the Somatic Nervous System

The SoNS contains both afferent nerves traveling towards the CNS and efferent nerves responsible for sending signals from the CNS towards the rest of the body. The brain and spinal cord process the input from a variety of sources and integrate them before devising a response. This response determines the location and strength of muscle contraction across different parts of the body. Therefore, the primary function of the somatic nervous system is to connect the CNS with organs and striated muscles in order to enable complex movements and behavior.

Additionally, the SoNS also mediates a subset of involuntary muscle responses called reflex arcs. A reflex arc results in an extremely quick muscle contraction in response to a stimulus, with minimal intervention from the brain. While the impulse for most voluntary muscle contraction originates in the brain or brainstem, a reflex action can be brought about with just a single sensory and motor neuron that synapse in the spinal cord. The motor response is practically ‘hard-wired’ for a particular stimulus. The knee-jerk response to the stimulation of the patellar ligament in the knee is an example of a reflex response. Other examples include the immediate withdrawal of a hand on touching a hot stove or a quick change in posture when the foot is placed on a sharp stone.

Examples of the Somatic Nervous System Response

The somatic nervous system is intricately linked to the central nervous system with the sensory and motor neurons of the SoNS communicating with the brain and spinal cord. Striated skeletal muscles under voluntary control receive signals to contract on the basis of stimuli relayed to the CNS. For instance, while walking in a tropical forest, you watch the forest floor for fallen twigs, insects or undergrowth. As the CNS constantly receives visual input, it sends messages to the peripheral nervous system, particularly the SoNS, to alter posture and contractility of skeletal muscle, and accommodate changes to the surface of the forest floor. At the same time, if a leech is stuck to your calf muscle, sensory neurons indicate the presence of a persistent damp feeling on your leg. Skeletal muscles act to alter your position so that the area can be visually inspected. On finding a leech, the CNS, through memory and learning, directs skeletal muscles of the arms and fingers through the SoNS to reach for some salt. Gross and fine motor skills are used to sprinkle a pinch of salt on the leech to ensure that it falls off.

Similar events are occurring within the nervous system in vastly varied activities. For example, a dancer on stage is integrating her memory of the music and choreography in the CNS to direct the movement of her skeletal muscles through the SoNS. From the still readiness of her body before the music begins till the last bow and smile, the neurons of the SoNS signal every large and small striated muscle group in the body based on the directions of the CNS.