The major divisions of the human nervous system are the central nervous system (CNS), the peripheral nervous system (PNS), and the autonomic nervous system (ANS). The CNS is made up of the brain and spinal cord. Both the PNS and the ANS carry information to and from the central nervous system. The PNS is generally concerned with the innervation of skeletal muscles and other muscles made up of striated muscle tissue, as well as sensory information from the periphery of the body. The ANS is that portion of the nervous system concerned with control of smooth muscle, cardiac muscle, and glands. The CNS (figure 11-4) is known as central because its anatomical location is along the central axis of the body and because the CNS is central in function. If we use a computer analogy to understand that it is central in function, the CNS would be the central processing unit and other parts of the nervous system would supply inputs and transmit outputs.

Figure 11-4. The human central nervous system.

a. Major Subdivisions of the CNS. The major subdivisions of the CNS are the brain and the spinal cord.

b. Coverings of the CNS. The coverings of the CNS are skeletal and fibrous.

c. Cerebrospinal Fluid (CSF). The CSF is a liquid thought to serve as a cushion and circulatory vehicle within the CNS.

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