Somatic Nervous System

Nervous system is the most important system in our body, and it is divided into central nervous system and peripheral nervous system. The central nervous system consists of brain and spinal cord. The peripheral nervous system is further divided into two major parts, the somatic nervous system (SNS) and the autonomic nervous system (ANS).

The SNS is made up of peripheral nerve fibers that send sensory information to the central nervous system and motor nerve fibers that send information to skeletal muscle. The main functions of the system are to control voluntary movements of your body and to help you feel through all your senses. The brain and the spinal cord are connected to the skeletal muscles and the external receptors with the nerves that belong to the SNS. This is the system that helps you feel the touch, smell, sight, taste and sound. The autonomic nervous system is further subdivided into sympathetic and parasympathetic nervous systems. A third division, the enteric nervous system, is also sometimes taken into consideration while studying the parts of the nervous system.

SNS Functions

The peripheral nervous system consisting of the SNS and the ANS, is made up of the nerves that lie just under the skin and the nerves that are spread everywhere else. Both these systems mostly operate automatically. The nerves belonging to SNS control voluntary body movements. It is observed that these somatic nerves which sense external stimuli, function automatically even in the event of a coma. As seen above, all five senses are controlled by the SNS. The system is responsible for the functioning of all sensory organs, including eyes, ears, tongue and skin. It controls the working of the skeletal muscles and of the muscles attached to the bone which are used for voluntary movements.

How does SNS function? During any movement, the SNS carries impulses from the brain to the muscle to be moved, while in its sensory capacity, the SNS carries impulses from the sensory organ to the brain. Thus there exist two types of neurons, the afferent and the efferent. The impulses from sense organs are carried to the central nervous system by afferent or sensory neurons and the impulses from the central nervous system are transmitted to the muscles by efferent or motor neurons. Neurons which comprise the SNS, emerge from the brain or spinal cord and reach the muscle or sense organ directly. Their cell body (the soma) is situated in the brain or spinal cord and the axons (long nerve filaments) travel to or from the cell body, ending in the muscle, skin or sense organ. They carry electrochemical impulses along with them. The average adult brain contains about 100 billion neurons!

SNS Disorders

Somatic nervous system disorders include diseases of the nerve roots, ganglia (A mass of nerve tissue or a group of neurons), sensory and motor nerves. A functional disorder and/or abnormal change that occurs in any region of the peripheral nervous system is called a neuropathy. If neuropathy involves only one nerve, it is called a mononeuropathy and if it involves several nerves, it is referred to as mononeuropathy multiplex or polyneuropathy. The most common SNS disorders are:

• Neuritis: Inflammation of a peripheral or cranial nerve.
• Cranial Nerve Diseases: Disorders and diseases of the cranial nerves, which are 12 in number and basically 'run' the head as well as help regulate the organs of the thoracic and abdominal cavities.
• Cranial Nerve Neoplasms: These disorders mainly consist of benign or cancerous growth in cranial nerve tissues. For instance: acoustic neuroma, optic nerve glioma, optic nerve meningioma.
• Diabetic Neuropathies : Peripheral and cranial nerve disorders associated with diabetes are common disorders. For instance, the common condition associated with diabetic neuropathy includes third nerve palsy, which affects the oculomotor nerve.
• Myasthenia Gravis : Myasthenia gravis disease or neuromuscular junction disease occurs when the body generates an immune system attack against its own skeletal muscles. It affects the transmission of the nerve impulses to muscle at the neuromuscular junction.
• Trigeminal Neuralgia : This is the most common neuralgia which affects the fifth cranial (trigeminal) nerve. Trigeminal neuralgia causes episodes of severe, stabbing, electric shock-like pain in the areas of the face where the branches of the nerve are distributed, that is lips, eyes, nose, scalp, forehead, upper jaw, and lower jaw.
• Brachial Plexus Neuropathies: The disorders of the peripheral nerve components of the brachial plexus, which consist of a group of lower neck and upper back spinal nerves that are responsible for communications with the arm, forearm and hand, can result in local pain, muscle weakness and decreased sensation in the upper extremity.

It is just impossible to describe somatic nervous system or any part of the nervous system in one article. I think, human nervous system, which includes brain, spinal cord, ten billion neurons and many times more interneural connections, is possibly the single most complex object in the entire cosmos.