Nervous System

The sophistication and the incredible dimensions of the human nervous system are the basis for the infinite range and subtlety of human movement. The nervous system, centered by the brain, generates every impulse that is directed into the musculoskeletal system for the stimulation of both muscular movement and reaction. The brain is the organ that operates the body; the human mind is the more intangible concept, connected to the physical organ and the nervous system, but extending into the aspects of intelligence, reasoning abilities, and human perception.

The brain is the most far-reaching organ in the body, with its influence and its control over every aspect of human function extended by way of the network that is the nervous system. Physical abilities that are at the essence of athletic ability, including muscular control, hand-eye coordination, reaction time, and the utilization of the body's composition of fast-twitch versus slow-twitch fibers, are all determined by the brain.

As the chief component of the nervous system generally, the brain is positioned at the top of the first branch of the nervous system, familiar as the central nervous system (CNS). The CNS has two parts, the

The human nervous system.
brain and the spinal cord, that extend from the region of the brain known as the brain stem, located at the base of the skull. The spinal cord runs through the spinal column, a bony protective structure, to the base of the spine at the pelvis. The spinal cord is primarily composed of nerve cells, known as neurons.

The brain is divided into a series of regions, each of which has a distinct responsibility for a function of the body. The cerebellum, located near the base of

A nerve cell.
the brain, is the learning center of the brain. The hypothalamus, connected to the pituitary gland, regulates body temperature and other functions that are a response to external stimuli. Whenever any of these control centers seek to transmit a message to another part of the body for action, the message begins it travel along the spinal cord.

The central nervous system is connected to a far more extensive nerve network. This structure is the peripheral nervous system. Unlike the central nervous system components, which are protected by the bone of the skull and the spine, the elements of the peripheral nervous system are not protected, extending through the tissue in pathways. The peripheral nervous system is a highly complex series of nerves and neurons that extend to every part of the body. The peripheral nervous system is itself subdivided into two major operational systems: the somatic (or voluntary) nervous system and the autonomic nervous system. The somatic system directs movement and the control of the skeletal muscles. The nerves that extend into the muscles ultimately terminate in a motor neuron, the device that transmits the particular instruction to the adjacent muscle fibers. The speed with which the particular neuron is designed to direct its impulses into the muscle fiber will dictate whether the fiber is a fast-twitch or slow-twitch fiber.

The other branch of the peripheral nervous system, the autonomic system, has three further subdivisions. As the name implies, the autonomic system is responsible for the regulation of a number of bodily functions that are either involuntary, or where the body generates an initial response that may be the subject of further voluntary action. The sympathetic nervous system includes the management of the body's "fight or flight" response, triggered when the brain, after receiving stimulation of a threat or other challenge, directs the production of adrenaline, the hormone that stimulates heart rate, respiratory function and the expansion of blood vessel capacity.

The counterpoint to the sympathetic nervous system is the parasympathetic nervous system, whose function is often summarized as the "rest and digest" response. After stimulation, the parasympathetic system acts to calm the body, through stimulation of the salivary gland to encourage eating and slowing the heart rate.

The third aspect of the autonomic system is sometime regarded as a separate nervous system, due to the nature of the organs that it controls. The enteric nervous system regulates the stomach and colon.

The nervous system functions as an entity, with the brain providing the ultimate direction. Although many nervous system functions are involuntary, damage to the central nervous system in particular can dramatically alter nervous system function as a whole. Much of the response of the nervous system to injury or impairment is one directional, for if the body senses damage to a lesser aspect of one of the subordinate components to the nervous system, it will endeavor to compensate; brain or spinal cord injuries do not permit alternate paths or compensatory routes.

SEE ALSO Motor control; Muscle fibers: Fast and slow twitch; Neck injuries.