The peripheral nervous system is the one of two big parties in which the nervous system is divided into. In turn it’s divided into the self nervous system, which controls the smooth muscles, internal organs, glands, and the somatic nervous system, which instead controls the voluntary movements and collects information from the sense organs. Its main function is to connect the central nervous system to the rest of the body.


What is the peripheral nervous system?

The peripheral nervous system consists of a set of nerve fibers and ganglia (clusters of cell bodies) of the somatic nervous system and the autonomic nervous system.


The somatic nervous system

The somatic nervous system consists of the nerve fibers that send sensory information towards the central nervous system and nerve fiber motor that the central nervous system then send to the skeletal muscles. These are formed by the extension of neurons (motor neurons or efferent neurons) located in the brain or spinal cord. The fibers of the sensory neurons (also called afferent) instead depart from neurons located at the level of ganglia, which receive information from a sensory receptor.


The autonomic nervous system

The autonomic nervous system is further divided into three parts: the sympathetic nervous system, the parasympathetic nervous system and enteric nervous system. This organization is more complex than that of the somatic nervous system and includes the presence of ganglia and preganglionic and post ganglionic fibers. The first are formed by the extensions of neurons whose bodies are localized in the central nervous system (the brain or spinal cord). These fibers are directed towards the ganglia, where they enter into communication with the body of neurons from which the extensions of postganglionic fibers are formed. These are directed finally to the designated organ.

In particular neurons of the sympathetic nervous system originate at the zone levels of thoracic and lumbar parts of the spinal cord. Only in a few cases have fibers contacting neurons been located far from the spine. The bodies of the neurons of the parasympathetic system are located in the sacral region of the spinal cord and the medulla oblongata of the brain stem. They leave fibers directed towards ganglia located near the organs that need to control certain functions of the body, from which the postganglionic fibers direct these signals towards the intended organs.

The enteric nervous system is instead formed by a network of fibers that innervate the viscera: the gastrointestinal tract, pancreas and gallbladder.

Contrary to the central nervous system, the peripheral nervous system is not protected by the skeleton, or similar systems regarding the blood-brain barrier. It is therefore exposed to the dangers associated with mechanical trauma and exposure to toxic substances.


What function does the peripheral nervous system serve?

The main function of the peripheral nervous system is to put in connection the central nervous system with the various parts of the organs and tissues in the body.

In particular, the somatic nervous system is responsible for the movements of all the voluntary muscles present in the organism. It also collects information from the senses, for example the receptors present in the skin. The somatic nervous system is also responsible for the so-called arc reflection method, which are the involuntary movements (such as the extension of the leg when a specific point below the knee is stimulated), they do not depend on a command from the brain but from the connection of a pathway to the bone cord.

The self-nervous system is responsible for all the functions of the body that are considered spontaneous and those that are reflected. Acting on the smooth muscles present around the internal organs, but also of those associated with hair follicles for example. They control vital functions such as breathing and heartbeat rhythm. The autonomic nervous system also controls the dilation of the pupils, and the production of secretions such as salvia and mucus, including the movements of the different parts of the digestive tract and the functioning of the bladder.

More particularly, the sympathetic nervous system allows us to react to situations of impending danger, and is responsible for several physiological changes such as increased heart rate and blood pressure and the sense of excitement due to the increase of adrenaline circulating in the organism (fight or flight). Acting in the complete opposite is the parasympathetic system, which is more active when a person is stationary (lying down on a bed) or feels relaxed and this is responsible for phenomena such as the narrowing of the pupil, the slowing down of the heart rate, dilation of blood vessels and stimulation of digestive and genitourinary functions. Finally, the enteric nervous system takes care of all aspects of digestion.