The evolution of hormones and the nervous system
Multicellular organisms need a way for cells [cell: Basic unit of life. Unicellular organisms only have one cell. Multicellular organisms have many cells. ] to communicate with one another. This has led to the development of nervous communication systems, as well as hormonalhormones: Chemical messengers produced in glands and carried by the blood to specific organs in the body systems.
The nervous system uses electrical impulses to bring about fast, but short-lived, responses. It consists of the:
Nerve cells are also called neurones. The diagram below shows a typical neurone. It has tiny branches at each end, and a long fibre to carry electrical signals.
Receptors are groups of specialised cells. They can detect changes in the environment, called stimuli, and turn them into electrical impulses. Receptors are often located in the sense organs such as the ear, eye and skin.
|Sense organs||Receptors sensitive to|
|touch, pressure, pain and temperature|
|chemicals in food|
|chemicals in the air|
|sound and position of the head|
Effectors are parts of the body that produce a response. Here are three examples:
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.