KEY CONCEPT The senses detect the internal and external environments.

The senses help to maintain homeostasis. Senses gather stimuli from the environment, and send it to the brain to read. Nervous system responds to stimuli. Pupils shrink when too much light enters the eyes. Goose bumps when cold air touches skin.

The senses detect physical and chemical stimuli. The eye contributes to vision. Photoreceptors sense light. Two photoreceptors work together: rod cells (sees black and white) and cone cells (sees color).

The ear contributes to hearing. mechanoreceptors called hair cells bend in response to vibrations

Taste and smell use chemoreceptors. Taste uses tongue, and smell uses nose. Chemoreceptors detect chemicals dissolved in fluid.

Mechanoreceptors detect pressure. The skin senses touch. Mechanoreceptors detect pressure. Pain receptors detect damaged tissue. Thermoreceptors detect temperature. pain receptor light pressure receptor hair follicle heavy pressure receptor