By mdkshareef on November 6th, 2010

Human Nervous System

Communication from one cell to another by chemical means was too slow to be adequate for survival, a system evolved that allowed for faster reaction. That system was the nervous system.

Nervous systems are of two general types, diffuse and centralized. In the diffuse type, found in lower invertebrate animals, there is no brain, and the nerve cells are distributed throughout the organism in a netlike pattern. In the centralized system of the higher invertebrates and the vertebrate animals, some portion of the nervous system has a dominant role in coordinating information and directing responses.

This centralization reaches its apogee in vertebrates, which have a well-developed brain and spinal cord. Impulses are carried to and from the brain and spinal cord by nerve fibres that make up the peripheral nervous system.

The general features of nervous systems-that is, their function of responding stimuli and the rather uniform electrochemical processes by which they carry out their response.