The peripheral nervous system consists of the sensory and motor neurons that transmit message to and from the central nervous system. Without the peripheral nervous system, our brain will be isolated from the world. It would not be able to receive any information and would not be able to control or show any activity. The peripheral nervous system has two divisions. They are the somatic nervous system and the autonomic nervous system.
The Somatic Nervous System:
The somatic nervous system consists of sensory neurons, which run from our sense organs towards the central nervous system for perception, learning etc. and the motor neurons, which carry messages from the brain towards the striped muscles of the body for activities. As a result, we are able to experience the beauties and horrors of the world and also show such actions like moving our hand or leg, singing, running, jumping, riding, and so on. Thus, the somatic nervous system in general controls the striated or striped muscles of our body.
The Autonomic Nervous System:
The autonomic nervous system regulates the glands and involuntary activities such as heartbeat, digestion, blood circulation etc. Thus, it controls the smooth muscles and glands of our body. The autonomic nervous system is called as autonomic because many of the activities it controls are autonomous or self-regulating and continue even when a person is asleep or unconscious. For example, digestion, blood circulation, etc. continue even when we are sleeping.
The autonomic nervous system has two divisions: sympathetic and parasympathetic nervous systems. Both these divisions have survival functions for which the autonomic nervous system is often called as survival nervous system. One is to assist the organism to escape or cope with a life-threatening situation. The other is to co-ordinate, produce and conserves the bodily resources necessary to maintain the organism throughout its life span.
The autonomic nervous system is intimately connected with the spinal cord. The sympathetic nervous system outflow takes place through the thoracic- lumbar regions of the spinal cord. The parasympathetic nervous system outflow takes place in the cranial-sacral regions of the spinal cord.
The sympathetic division tends to act as a unit; it is excited in emotional situations. Thus, sympathetic nervous system is the division for emergency survival. During emotional excitement, for example, the digestion is stopped, heart-rate is increased, the arteries of the heart and skeletal muscles are dilated, blood flowing to the internal organs is redirected to the skeletal muscles, the air passages in the lungs are opened to facilitate oxygen transfer and the endocrine system (ductless glands) is stimulated to release several chemicals that increase the effectiveness of the entire motor system.
Unlike the sympathetic nervous system, the parasympathetic system tends to affect one organ at a time. Whereas the sympathetic system is activated during violent emotions or excited activities, the parasympathetic system is dominant and active during normal times or during quiescence. It stimulates processes that conserve the body’s energy. Activation of this system slows heartbeat, lowers blood pressure and diverts blood away from skeletal muscles to the digestive system, conserves and protects bodily resources.
At first glance it appears that the sympathetic and parasympathetic systems compete with one another in a head-on clash. In fact, this is far form the case. The sympathetic and parasympathetic systems actually function in a coordinated manner. For example, if a person eats a very large meal in a •east, the parasympathetic system stimulates digestion while at the same time the sympathetic system increases sweating in order to eliminate excess heat.