Crystalfish 06:04, 12 December 2008 (UTC)The nervous system is the human body's quick transmission system that make the body aware of its experience of itself (hunger, thirst, pain) as well as its experience of the environment(heat, light, predator, etc.).It also enables the body to react to these various stimuli. The nervous system is didvded into two sections,the central nervous syetem (CNS) and the peripheral nervous system (PNS).The central nervous system consists of the brain and spinal cord while the PNS consists of all the nerve fibers that allow the CNS to communicate with the rest of the body.
The Nervous system is a highly complex network of specialized cells called neurons. The functions of the nervous system can be studied under three main categories – (1) survival and regulation of internal organ function; (2) response to the external environment and (3) in humans, facilitating higher functions like thinking, reasoning, consciousness, etc.
The PNS consists of all the spinal and cranial nerves. It can further be divided into two parts based on the functions.
(1) The somatic nervous system consists of nerves that connect the voluntary muscles to the central nervous system enabling the individual to move the parts of the body to perform actions at will. The sensory fibres of this system come from the major receptor organs like the eye, ears, touch receptors etc., the motor fibres of the somatic system are connected to the striated muscles that move the arms, legs, etc. This system also works in congruence with the autonomous nervous system during emotional arousal (e.g., muscle tension and faster breathing during strong emotional arousal)
(2) The autonomous nervous system which is involved in regulating and maintaining the involuntary actions of the body like digestion, heartbeat, blood pressure, etc. The autonomous nervous system is further made up of two distinct parts – the sympathetic and the parasympathetic nervous systems. The sympathetic nervous system prepares the body to expend energy in response to a stimulus (e.g., to meet the energy requirement of running away from danger) while the parasympathetic nervous system brings the body back to a relaxed state and helps to conserve energy. Together, these two systems work in coordination to enable us to respond appropriately to thousands of stimuli everyday. However, they are also actively involved in the process of emotional arousal (even in the absence of an immediate external stimulus) and subsequent relaxation. Memory of a recent traumatic incident like a traffic accident can trigger an emotion of fear and the corresponding sympathetic activity like higher heart rate, higher blood pressure, etc., even if the individual is comfortably seated in the safety of his home.
For a more detailed description, consult the Fundamentals of Neuroscience course.