The cells in multicellular organisms do not work independently of each other. In animals for example, muscle cells in the legs depend on red blood cells in the blood to supply them with oxygen and neurons in the brain to make them contract.
To ensure that all the cells in a multicellular organism function correctly for the survival of an organism, the cells need systems for communication with each other.
The building blocks of the nervous system are neurons (nerve cells). Neurons are specialised to allow rapid communication between cells in different parts of the body by transmitting electrical impulses.
There are three types of neurons:
Some neurons are specialised to allow them to detect changes in environmental factors such as light, sound and temperature. These neurons are found in sense organs.
The function of the Central Nervous System (CNS) is:
Muscles produce rapid responses by contracting. Glands produce responses more slowly by releasing chemicals.