Starting from the brain, different parts of nervous system descend downward and reach all the major and minor parts of the body with the help of neurons or nerve cells. For the purpose of convenience and comprehension, you can divide the communication complex into central and peripheral parts or organs. The central nervous system parts (brain and spinal cord) are combined to form the central nervous system, while the peripheral parts lead to the formation of peripheral nervous system.

Parts of Central Nervous System

The primary parts of the CNS are brain and spinal cord where the former is enclosed and protected by a hard, rounded bony shell, called skull, while the latter is given protection by your vertebral columns.

Brain

In relation to body size, the brain in humans is larger than that of any other bilaterally symmetrical animals, living on the planet earth. But there is no denying the fact that the supreme organ of your body has almost the same general structure as found in other such organisms. The brain of an adult human measures on average as heavy as 1.5 kg (3 pounds) in mass, while its volume shows variation on the basis of gender where the males have comparatively larger brain than that of females.

Many of the special features of human brain show similarity with those of other mammalian brains, such as, six-layer cerebral cortex, presence of hippocampus & amygdale, and its basic division into three parts, namely, midbrain, forebrain and hindbrain.

Spinal Cord

Extending from the medulla oblongata of your brain, it is a tubular bundle of thin and long nervous tissues along with the support cells. Going along and protected by your backbone, it does not run the entire length of the vertebral column and terminates at the point between the first and second lumbar vertebrae. The overall length of this part of the CNS shows variation on the basis of gender, that is, its average length in males reaches up to 18 inches (45 centimeters), while in female adults it is about 17 inches (43 centimeters).

If you move from top to bottom, the thickness of neural column goes on decreasing gradually and becomes thinnest at the point of thoracic vertebrae. Though primary function of the spinal cord is to ensure the transmission of signals between the brain and remaining parts of the body, it is also found to act independently for controlling central pattern generators and various reflexes.

Parts of Peripheral Nervous System

Developing connection between the CNS and all the extremities of the body, it is divided into three subsystems (sensory, somatic and autonomic nervous system) that are made up of following parts:

Spinal Nerves

Forming one of the three major parts of the somatic nervous system, these peripheral nerves carry sensory information into the spinal cord.

Cranial Nerves

These nerve fibers of the somatic system are used to carry information into and out of the brain stem, and include smell, vision, taste, and so on.

Association Nerves

The integration of sensory input and motor output takes place in these nerve fibers of the somatic nervous system.

Sensory Receptors

It is a specialized type of sensory nerve ending of the sensory system that initiates sensory transduction in response to a stimulus in external or internal environment of an organism.

Neural Pathways

Also called white matter, these bundles of elongated neurons serve to connect one part of the nervous system or brain with another distant part.