Nervous system: Encyclopedia II - Nervous system - Vertebrate nervous systems

Nervous system - Vertebrate nervous systems

The nervous systems of vertebrate animals are often divided into a central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS consists of all other nerves and neurons that do not lie within the CNS. The large majority of what are commonly called nerves (which are actually axonal processes of nerve cells) are considered to be PNS. The peripheral nervous system is divided into the somatic nervous system and the autonomic nervous system.

The somatic nervous system is responsible for coordinating the body's movements, and also for receiving external stimuli. The autonomic nervous system is the involuntary part of the nervous system where all of the internal maintenance is taken care of.

The autonomic nervous system is then divided into the sympathetic division and parasympathetic 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.

Adapted from the Wikipedia article "Vertebrate nervous systems", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki