The Senses Sensory Receptors Sensory receptors neurons that

The Senses

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

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

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.

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

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

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

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

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

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

• 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.

Hearing video • http: //www. youtube. com/watch? v=qgdqpo. Pb 1 Q

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

• 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

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