CNS is shown in red and PNS in blueNervous system is a network of specialized cells that conducts stimuli from parts of the body to the brain and spinal cord, and impulses back to other parts of the body.
It is composed of neurons and other specialized cells called glial cells (plural form glia) that aid in the function of the neurons.
The nervous system is divided broadly into two categories: the Peripheral nervous system (PNS) and the Central nervous system (CNS). Neurons generate and conduct impulses between and within the two systems.
CNS
The CNS is the largest part of the nervous system, and includes the brain and spinal cord. The spinal cavity holds and protects the spinal cord, while the head and protects the brain. The CNS is covered by the meninges, a three layered protective coat and float in a crystal-clear cerebrospinal fluid. The brain is also protected by the skull, and the spinal cord by the vertebrae.
PNS
The PNS is a regional term for the collective nervous structures that do not lie in the CNS. They are the set of neurons that connect the CNS to the limbs and organs. They include the 12 cranial nerves which orginate from brain and 31 pairs of spinal nerves that orginate from spinal cord.
Neurons
Neurons are electrically excitable cells in the nervous system that process and transmit information. Neurons are the core components of the brain, the spinal cord, and the peripheral nerves.
A number of different types of neurons exist,
Sensory neurons respond to touch, sound, light and numerous other stimuli effecting sensory organs and send signals to the spinal cord and brain.
Motor neurons receive signals from the brain and spinal cord and cause muscle contractions and affect glands. Interneurons connect neurons to other neurons within the brain and spinal cord.
Glial cells
Glial cells are non-neuronal cells that provide support and nutrition, maintain nerve cells, form myelin, and participate in signal transmission in the nervous system. In the total human brain, the number of glia is estimated to be roughly the same as neurons.
Glial cells provide support and protection for neurons. They are thus known as the "glue" of the nervous system. The four main functions of glial cells are to surround neurons and hold them in place, to supply nutrients and oxygen to neurons, to insulate one neuron from another, and to destroy pathogens and remove dead neurons.
