The Nervous System

The nervous system is a complex collection of nerves and specialized cells known as neurons that transmit signals between different parts of the body. It can be considered to be made up of two parts: the central nervous system and the peripheral nervous system. The central nervous system is made up of the brain, spinal cord and nerves. The peripheral nervous system of sensory neurons and clusters of such neurons (ganglia) and nerves that connect to one another and to the central nervous system. The following outline follows the content of Audesirk & Audesirk.

The nervous system has two main subdivision: the somatic, or voluntary, component, and the autonomic, or involuntary, component. The autonomic nervous system regulates many body process such as blood pressure and rate of breathing, that work without conscious effort. The somatic system consists of nerves that connect the brain and spinal cord with muscles and sensory receptors in the skin.

The primary function of the autonomic nervous system is homeostasis. It has two divisions: the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system accelerates heart rate, constricts blood vessels, and raises blood pressure, and other functions of a generally stimulating nature. The parasympathetic nervous system slows heart rate, increases intestinal and gland activity, and other inhibitory or calming functions.

The Autonomic Nervous System

The autonomic nervous system regulates many body process such as blood pressure and rate of breathing, that work without conscious effort. The primary function of the autonomic nervous system is homeostasis. It has two divisions: the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system accelerates heart rate, constricts blood vessels, and raises blood pressure, and other functions of a generally stimulating nature. The parasympathetic nervous system slows heart rate, increases intestinal and gland activity, and other inhibitory or calming functions. The illustration of the pathways for the sympathetic and parasympathetic systems below follows the organization of Audesirk & Audesirk.

The Central Nervous System

The human nervous system can be considered to be made up of two parts: the central nervous system and the peripheral nervous system. The central nervous system is made up of the brain, spinal cord and nerves.

The Somatic Nervous System

"The somatic motor nervous system includes all the voluntary motor pathways outside the CNS. That is, it involves the peripheral pathways to the skeletal muscles, which are the somatic effectors" (T&P) The somatic nervous system includes both sensory nerves (afferent nerves) which relay sensation from the muscles to the CNS and nerves which send out commands (efferent nerves) to stimulate muscle contraction.

The somatic nerves can be considered as 43 segments, 31 in the spinal cord and 12 in the brain stem. The main neurons connect to thousands of other supporting nerves throughout the body. These segments will contain both sensory and motor neurons, with the sensory neurons providing feedback to facilitate control of the motor function. Part of these control frameworks are neural circuits called reflex arcs. These reflex arcs can involve interneurons connecting the sensory and motor neurons within the body. Perhaps the most familiar is the patellar reflex or "knee jerk" reaction where tapping the patellar tendon quickly activates the muscles of the thigh to produce a kick. Some of these contribute a protective function, like removing the hand after touching a hot surface.