B10

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B10.1

Homeostasis is the maintenance of a constant internal environment. Organs cannot work if conditions in the internal environment keep changing.

Important to respond to changes in the internal or external environment to maintain optimum conditions for the cellular enzymes.

Internal conditions that are controlled:

- body temperature

- water content of body

- blood glucose concentration

What control systems in the body need:

Receptors: cells that detect changes in the internal or external environment. Changes are known as stimuli. Receptors may be part of the nervous or hormonal control systems of the body.

Coordination centres: areas that receive and process the information from the receptors. Send out signals and coordinate the response of the body. Includes the brain, a coordination centre for nervous system and part of the hormonal system, spinal cord, and some organs such as the pancreas.

Effectors: muscles or glands that bring about responses to the stimulus that has been received. These responses restore conditions in the body to the optimum levels.

Página 2

B10.2

Receptor cells have a nucleus, cytoplasm, and a cell membrane.

When a stimulus is detected, the information is sent as an electrical impulse that passes along special cells called neurones. Usually found in bundles known as nerves.

Impulse travels along the neurone until it reaches the central nervous system (CNS). CNS is made up of the brain and spinal cord. The cells that carry impulses from the your sense organs to your CNS are called the sensory neurones.

Brain gets a lot of info from sensory receptors in the body. It coordinates a response and sends impulses out along cells called motor neurones. These carry information from CNS to the rest of the body. They carry impulses to make the effectors respond. Muscles respond to the arrival of impulses by contracting. Glands respond by secreting chemical substances.

Stimulus - receptor - coordinator