1. The Senses (3) Anatomy and Physiology

2. The Senses  The body contains millions of neurons that react directly to stimuli from the environment, including light, sounds, motion, chemicals, pressure, and changes in temperature.  These neurons are called sensory neurons, which react to specific neurons and eventually to the CNS. The sensory receptors are located throughout the body and are concentrated in the sense organs. (eyes, ears, mouth, nose, and skin)

3. The Senses  There are 5 categories of sensory receptors: –Pain receptors (respond to chemicals released by damaged cells) –Thermoreceptors (detect variation in body temperature) –Mechanoreceptors (sensitive to touch, pressure, stretching of muscles, sound and motion) –Chemoreceptors (sensitive to chemicals in the external environment) –Photoreceptors (sensitive to light)

4. Vision  Eyes are a sense organ used to sense light  Light enters the eye through the cornea, which helps focus the light  The impulses created by the light leave each eye by the optic nerve  The optic nerve then carries the impulses to the appropriate parts of the brain  The brain interprets the impulses as visual images and provides info about the external world

5. Structures of the Eye  Cornea  tough transparent layer of cells that helps focus light  Aqueous Humor  chamber filled with fluid that is located behind the cornea  Iris  a disk-like structured that is the colored eye  Pupil  small opening that is adjusted by tiny muscles which regulate the amount of light that enters the eye

6. Structures of the Eye  Lens  has small muscles attached to it and allow it to change its shape to help you adjust your eye’s focus to see near or distant objects  Retina  photoreceptors are arranged in a layer and convert light energy into nerve impulses that get sent to the CNS  Fovea  site of the sharpest vision  Optic Nerve  passes through the back of the eye and there is no photoreceptors (blind spot)

8. 2 Types of Photoreceptors  Rods  extremely sensitive to light but do not distinguish colors  Cones  less sensitive and respond to light of different colors producing color vision (concentrated in the fovea)

10. Hearing and Balance  Sound is nothing more than vibrations in the air around us.  The ear is the sensory organ that can distinguish both the pitch and loudness of those vibrations  Vibrations enter the auditory canal

11. Structures of the Ear  Tympanum  (eardrum) vibrations from the external environment cause vibrations in the tympanum  Hammer, anvil, and stirrup  tiny bones that pick up vibrations from the tympanum.  Oval Window  picks up vibrations from the stirrup and causes pressure waves in the fluid of the cochlea

12. Structures of the Ear  Cochlea  fluid filled and found in the inner ear. It is lined with tiny hair cells that are pushed back and for the by pressure waves. The hair cells then produce nerve impulses that are sent to the brain throught he cochlear nerve.

14. Balance  Within the inner-ear just above the cochlea are three canals at right angles to one another called semicircular canals.  The canals and 2 tiny sacs located behind them monitor the position of your body, especially your head in relation to gravity.

15. Balance  The canals and sacs are filled with a fluid and lined with hair cells. As the head changes position. The fluid also changes position, which causes the hair on the hair cells to bend. This action sends impulses to the brain that enable it to determine body motion and position.

16. Smell  Your sense of smell is actually a ability to detect chemicals. Chemoreceptors in the lining of the nasal passageway respond to specific chemicals and send impulses to the brain through sensory nerves.  The “taste” of food and drink is actually smell

17. Taste  The sense of taste is a chemical sense.  The sense organs that detect taste are the taste buds, most of which are located on the tongue, but a few are in other locations of the mouth.  Tastes are: salty, bitter, sweet, and sour.

19. For Your Information:  Be ready for stations next class, where we will be discovering the effects of drugs on the nervous system.  You need to be familiar with lectures: 1, 2, and 3 in order to be successful. Tonight complete the review paper for homework.