Although the nervous system functions as a coordinated whole, it is divided into anatomical and functional divisions as an aid in understanding this complex organ system.
The nervous system has two major anatomical divisions. The central nervous system (CNS) consists of the brain and spinal cord. The CNS is the body’s neural integration center. It receives incoming information (nerve impulses), analyzes and organizes it, and initiates appropriate action. The peripheral nervous system (PNS) is located external to the CNS and consists of cranial and spinal nerves, ganglia, and sensory receptors. The PNS carries nerve impulses formed by sensory receptors, such as pain and sound receptors, to the CNS. It also carries nerve impulses from the CNS to effectors, which are the muscles, glands, and adipose tissue.
Similarly, the nervous system is divided into two major functional divisions. The sensory division carries nerve impulses from sensory receptors to the CNS. Somatic sensory information is collected by sensory receptors within the skin, skeletal muscles, bones, and joints. Visceral sensory information is collected by sensory receptors in the viscera in the ventral cavity, in the walls of blood vessels, and within the CNS. The motor division carries nerve impulses from the CNS to effectors, which perform an action. The motor division is further divided into two subdivisions. The somatic nervous system (SNS) is involved in the voluntary (conscious) control of skeletal muscles. The autonomic nervous system (ANS) provides involuntary (subconscious) control of cardiac muscle, smooth muscle, adipose tissue, and glands (figure 8.1).