1. The Senses

2. Sensory Receptors Sensory receptors = neurons that react directly to stimuli from the environment. – Light, sound, motion, chemicals, pressure and changes in temperature

3. 5 categories of sensory receptors Pain receptors = react to chemicals released by damaged cells Thermoreceptors = detect variations in temperature Mechanoreceptors = sensitive to touch, pressure, stretching of muscles, sound and motion Chemoreceptors = sensitive to chemicals (taste/smell) Photoreceptors = sensitive to light

4. Vision Eyes are the organ used to sense light Lights enters through the cornea which helps focus the light The iris is at the back of the eye and is the colored part In the middle of the iris is a small opening called the pupil The iris can adjust its size to control the amount of light the pupil lets in the eye.

5. Lens Behind the iris is the lens. The lens changes its shape to help you adjust your eyes’ focus to see near or distant objects The lens focuses the light onto the retina

6. Retina The retina receives the light and turns the light energy into nerve impulses It is lined with photoreceptors that convert the light to nerve impulses – Two types of photoreceptors Rods = sensitive to light but not color Cones = respond to light of different colors producing color vision

7. Video how light enters your eye http://www.teachertube.com/video/how- light-enters-the-eye-542 http://www.teachertube.com/video/how- light-enters-the-eye-542

8. Ears Your ears has two functions: hearing and balance Sound is vibrations in the air. Your ears can distinguish both pitch and loudness of those vibrations

9. Hearing Vibrations enter your auditory (ear) canal and cause your tympanum (ear drum) to vibrate Three bones, the hammer, anvil and stirrup transmit the vibrations to the oval window The vibrations create pressure waves n the fluid filled cochlea The tiny hair cells which line the cochlea move due to the waves and cause a nerve impulse

10. Balance Semicircular canals are located above the cochlea they have two small sacs located behind them and together they monitor the position of you body and head

11. The semicircular canals and sacs are filled with fluid and lined with hairs When your head changes positions the fluid moves because of it The fluid bends the hairs and it moves, which sends impulses to the brain The brain uses these impulses to determine body motion and position.

12. Hearing video http://www.youtube.com/watch?v=qgdqp- oPb1Q http://www.youtube.com/watch?v=qgdqp- oPb1Q

13. Smell and Taste Both smell and taste is the organs sensing chemicals smell is done by chemoreceptors in your nasal passage that send impulses to the brain Most of what we think is taste is actually smell

14. Taste is done by chemoreceptors called taste buds Taste buds are mainly found on the tongue, but some are found throughout the mouth Taste is detected in four categories: – Salty, bitter, sweet, and sour

15. Touch Touch is not found in one particular place All you skin is sensitive to touch Skin has sensory receptors that respond to temperature, touch and pain Your face, fingers and toes have a larger number of receptors and therefore are more sensitive to touch