Nervous system is the chief controlling and coordinating system of the body. It controls and regulates all activities of the body, whether voluntary or involuntary, and adjusts the individual (organism) to the given surroundings. This is based on the special properties of sensitivity, conductivity and responsiveness of the nervous system.
The protoplasmic extensions of the nerve cells form the neural pathways called nerves. The nerves resemble the electricity wires. Like the electric current flowing through the wires, the impulses (sensory and motor) are conducted through the nerves.
The sensory impulses are transmitted by the sensory (afferent) nerves from the periphery (skin, mucous membranes, muscles, tendons, joints, and special sense organs) to the central nervous system (CNS). The motor impulses are transmitted by the motor (efferent) nerves from the central nervous system to the periphery (muscles and glands).
Thus the CNS is kept continuously informed about the surroundings (environment) through various sensory impulses, both general and special. The CNS in turn brings about necessary adjustment of the body by issuing appropriate orders which arc passed on as motor impulses to the muscles, vessels, viscera and glands. The adjustment of the organism to the given surroundings is the most important function of the nervous system, without which it will not be possible for the organism ta survive.
Parts of Nervous System:
The nervous system is broadly divided into central and peripheral parts which are continuous with each other. Further subdivisions of each part are given below.
Central nervous system (CNS) includes:
- Brain or encephalon, which occupies cranial cavity, and contains the higher governing centers.
- Spinal cord or spinal medulla, which occupies upper two-thirds of the vertebral canal, and contains many reflex centers.
Peripheral nervous system (PNS) includes:
- Cerebrospinal nervous system is the somatic component of the peripheral nervous system, which includes 12 pairs of cranial nerves and 31pairs of spinal nerves. It innervates the somatic structures of the head and neck, limbs and body wall, and mediates somatic sensory and motor functions.
- Peripheral autonomic nervous system is the visceral component of the peripheral nervous system, which includes the visceral or splanchnic nerves that are connected to the CNS through the somatic nerves. It innervates the viscera, glands, blood vessels and non-striated muscles, and mediates the visceral functions.