C ONTROL AND C OORDINATION Chapter 5 Lesson 2

O BJECTIVES List the sensory receptors in each sense organ. Explain what type of stimulus each sense organ responds to and how. Explain why healthy senses are needed.

S ENSE O RGANS Light rays, sound waves, heat, chemicals or pressure that comes into your personal territory will stimulate your sense organs. Sense organs are adapted for interpreting these different stimuli.

S EEING - T HE E YE Retina - tissue at back of eye that is sensitive to light Rods -Respond to dim light, also help one to detect shape and movement Cones - Respond to bright light and color Optic Nerve Carries impulses to visual area of the cortex

T HE E YE Light enters eyes Passes through the cornea Light is refracted Light passes through the lens and is refracted again Light is directed toward the retina. Rods respond to dim light and cones respond to bright light and color Light impulse passes Through the optic nerve Visual area of cortex In the cerebrum

L ENSES Convex lenses are shaped so that the rays converge together(F is the focal point) Concave lenses are shaped to spread rays apart.

N EARSIGHTEDNESS Eyeball is too long from front to back Light from objects is focused in front of the retina. Image that reaches the retina is blurred. Concave lenses are used to correct the problem.

F ARSIGHTEDNESS Eyeball is too short from front to back. Light from objects is focused behind the retina Convex lenses correct farsightedness.

C ATARACTS Normally, the lens of the eye is clear. When a cataract develops, the lens becomes cloudy, similar to a frosted window. Located near the front of the eye, the lens focuses light on the retina at the back of the eye. Light passes through it to produce a sharp image on the retina. When a cataract forms, the lens can become so opaque and unclear that light cannot easily be transmitted to the retina. Often, however, a cataract covers only a small part of the lens and if sight is not greatly impaired, there is no need to remove the cataract. If a large portion of the lens becomes cloudy, sight can be partially or completely lost until the cataract is removed.

G LAUCOMA Glaucoma usually occurs when intraocular pressure increases. This happens when the fluid pressure in the eye's anterior chamber, the area between the cornea and the iris, rises.

G LAUCOMA Normally, this fluid, called aqueous humor, flows out of the eye through a mesh-like channel. If this channel becomes blocked, fluid builds up, causing glaucoma. The direct cause of this blockage is unknown, but doctors do know that it is most often inherited, meaning it is passed from parents to children. The increased pressure, called intraocular pressure, can damage the optic nerve, which transmits images to the brain. If damage to the optic nerve from high eye pressure continues, glaucoma will cause loss of vision. Without treatment,

H EARING Sound waves are necessary for hearing sound. Sound energy is to hearing as light energy is the seeing. When sound waves reach the ear, they stimulate nerve cells deep within your ear.

P ROCESS OF H EARING Outer ear Intercepts sound waves and funnels them down the canal to the middle ear. Eardrum vibrates Vibrations move the anvil, stirrup and hammer in the middle ear. Vibrating stirrup causes fluids in the cochlea to vibrate Hair cells in cochlea vibrate Electrical impulses sent to the brain by a nerve

H EARING - T HE E AR

B ALANCE - C ONTROLLED BY I NNER E AR Cristae ampullaris Contain tiny hair cells React to rotating body movements Gel-like fluid surrounding hair cells moves and stimulates the nerve cells at the base of the hair cells. Maculae Contain tiny hair cells React to the tipping or tilting of the head

S MELL One smells food because it gives off molecules into the air. These molecules stimulate sensitive nerve cells called olfactory cells in your nasal passages. These cells are kept moist with mucus.

T ASTE Taste buds Major sensory receptors for taste. FoodMouth begins to water Saliva and food wash over the taste buds Impulses sent to the brainYou identify the taste

T ASTING F OOD The five taste sensations are sweet, salty, sour, bitter, and the taste of MSG.

O THER S ENSORY R ECEPTORS IN THE B ODY Your internal organs have several kinds of sensory receptors. These receptors respond to touch, pressure, pain and temperature. They pick up changes in touch, pressure, pain and temperature and transmit impulses to the brain and spinal cord. Your body then responds to this new information.

Question What are the sensory receptors for the nose and eyes? Answer Nose- olfactory cells Eyes- rods and cones

Question Why is it important to have sensory receptors for pain and pressure in your internal organs? Answer Internal sensory receptors alert the brain when something is wrong. This allows the body to respond and protect itself and to maintain homeostasis.