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( Peripheral nervous system)
The peripheral nervous system (PNS) can be divided into the somatic nervous system and the autonomic nervous system (ANS). The PNS is not protected by bone, leaving it exposed to injury, unlike the central nervous system, which is made of the brain and spinal cord, to serve the limbs and organs. [1] The peripheral nervous system can be classified either by direction of neurons or by function. There are three types of directions of the neurones By function, the peripheral nervous system is divided into the somatic nervous system , autonomic nervous system and the enteric nervous system. The somatic nervous system is responsible for coordinating the body movements, and also for receiving external stimuli. It is the system that regulates activities that are under conscious control. The autonomic nervous system is then split into the sympathetic division, parasympathetic division, and enteric division. The sympathetic nervous system responds to impending danger or stress, and is responsible for the increase of one's heartbeat and blood pressure, among other physiological changes, along with the sense of excitement one feels due to the increase of adrenaline in the system. The parasympathetic nervous system, on the other hand, is evident when a person is resting and feels relaxed, and is responsible for such things as the constriction of the pupil, the slowing of the heart, the dilation of the blood vessels, and the stimulation of the digestive and genitourinary systems. The role of the enteric nervous system is to manage every aspect of digestion, from the esophagus to the stomach, small intestine and colon.
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