KEY CONCEPT The senses detect the internal and external environments.

The senses help to maintain homeostasis. Senses gather stimuli, and send it to the nervous system. 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 and cone cells. Rod cells detect light cone cells detect color

70 % of sensory receptors are for vision The way we see: 1. light enters the cornea 2. Then it passes through the pupil, then the lens and then the retina 3. In the retina the rod and cone cells stimulate the optic nerve . 4. The optic nerve carries the impulse to the brain, which interprets the impulse.

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

How we hear: 1. The outer ear (pinna) collects sound waves, sends them down the auditory canal to the eardrum, which sends them to the middle ear. 2. The middle ear has three bones that amplify the sound wave and pass it to the inner ear. 3. The inner ear has the cochlea which is filled with fluid. The vibrations move the fluid, which moves hair inside the cochlea, which create a nerve impulse, which is sent to the brain.

The ear also controls balance with the semicircular canals.

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 chemicals released bydamaged tissue. Thermoreceptors detect temperature. pain receptor light pressure receptor hair follicle heavy pressure receptor