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Human Body
Structural Organization
The structural arrangement of the nervous system is the basis for its division into two parts:
1. Central Nervous System (C.N.S.) consisting of the brain and the spinal cord.
2. Peripheral Nervous System (P.N.S.) consisting of 31 pairs of spinal nerves, 12 pairs of cranial nerves.
The functional relationships are the basis for differentiation of another division, the autonomic nervous system. The Central Nervous System
The brain and spinal cord merge smoothly into one another without any obvious demarcation; the portion above the foramen magnum (the opening in the base of the skull) is considered as the brain while the portion below it is the spinal cord. The brain directs all conscious movements, and a number of unconscious, in voluntary actions as well
The spinal cord, a shining rope of nerve cells, runs along the channel formed by the vertebral column.
The Peripheral Nervous System consists of the numerous nerves, that branch out from the brain and spinal cord forming the network throughout the body. The P.N.S. includes (i) the cranial and spinal nerves which carry messages to and from the C.N.S. and (ii) the autonomic nerves, which carry messages only from the C.N.S. There are hundreds of peripheral nerves which branch and rebranch, after leaving the brain or spinal cord, to form an intricate network.
The Autonomic Nervous System-Some of the most vital activities of the body, viz., breathing, beating of the heart, the digestion of food, and the formation of urine are normally carried automatically without our giving them much conscious thought. The activities of the internal organs are the province of a special division of the nervous system called the autonomic nervous system. The action of this system is not generally under voluntary control. The autonomic fibres are linked with and controlled by the hypothalamus, a part of the brain.
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