1 The Sensory System Chapter 11

2 The Sensory System: Protects us by detecting changes in the environment Protects us by detecting changes in the environment Some stimuli arrive from the external environment & are detected at or near the surface of the body Some stimuli arrive from the external environment & are detected at or near the surface of the body Other stimuli can originate internally & help to maintain homeostasis Other stimuli can originate internally & help to maintain homeostasis Regardless of the type of stimulus, sensations must be interpreted by the cerebral cortex in order for us to experience any feeling Regardless of the type of stimulus, sensations must be interpreted by the cerebral cortex in order for us to experience any feeling RECEPTORS detect a stimulus RECEPTORS detect a stimulus

3 Special Senses Localized in a “special sense” organ Localized in a “special sense” organ Vision: receptors in the eye Vision: receptors in the eye Hearing & Equilibrium: receptors in the internal ear Hearing & Equilibrium: receptors in the internal ear Taste: receptors on the tongue Taste: receptors on the tongue Smell: receptors in upper nasal cavities Smell: receptors in upper nasal cavities

4 General Senses Widely distributed throughout the body Widely distributed throughout the body Pressure, heat, cold, pain & touch: receptors in the skin & internal organs Pressure, heat, cold, pain & touch: receptors in the skin & internal organs Body positioning: receptors in muscles, joints & tendons Body positioning: receptors in muscles, joints & tendons

5 The Eye & Vision Protection of the eyeball –Skull bones form the eye ORBIT (cavity) protects more than half of the dorsal part of the eyeball

6 –Eyelids protect the front of the eye keeping harmful particles out & lubricate the eyeball through blinking –Eyelashes & eyebrows assist in keeping foreign matter out of the eye

7 Lacrimal Glands Produce tears which lubricate the eye, wash away small foreign objects & contain an enzyme that helps protect against infection Produce tears which lubricate the eye, wash away small foreign objects & contain an enzyme that helps protect against infection

8 Coats of the Eyeball Sclera “white of the eye” Outermost coat Made of tough connective tissue

Choroid Composed of delicate tissue with many blood vessels Composed of delicate tissue with many blood vessels Contains dark brown pigment Contains dark brown pigment Prevents incoming light from scattering & reflecting off the inner surface of the eye Prevents incoming light from scattering & reflecting off the inner surface of the eye Lies between the sclera & the retina Lies between the sclera & the retina

10 3. Retina Innermost coat Innermost coat Receptor layer of the eye Receptor layer of the eye Contains & which generate nerve impulses in order for vision to occur Contains RODS & CONES which generate nerve impulses in order for vision to occur

11 Refraction As light passes toward the retina, it undergoes a process called As light passes toward the retina, it undergoes a process called REFRACTION The bending of light rays as they pass from one surface to another Allows light from a large area to be focused on a small surface (the retina) where sight receptors are located

12 Refracting Parts of the Eye Cornea – the “window of the eye” Main refracting structure Bulges forward slightly Has no blood vessels Nourished by fluids that wash over it

13 2. Aqueous Humor Watery fluid that fills much of the eyeball in front of the lens Helps to maintain the slight forward curve of the cornea

14 3. Lens (Crystalline Lens) Clear, circular structure made of firm, elastic material Clear, circular structure made of firm, elastic material Important in light refraction as it can adjust to focus light for both near & distant vision Important in light refraction as it can adjust to focus light for both near & distant vision

15 4. Vitreous Body Soft, jelly-like substance that fills the entire space behind the lens Soft, jelly-like substance that fills the entire space behind the lens Important in maintaining the shape of the eyeball Important in maintaining the shape of the eyeball Aids in refraction Aids in refraction

16 Muscles of the Eye – voluntary muscles attached to the outer surface of the eyeball Extrinsic Muscles – voluntary muscles attached to the outer surface of the eyeball –Seven extrinsic muscles ORIGINATE on the bones of the ORBIT & INSERT on the surface of the SCLERA –These muscles pull on the eyeball in coordination with each other –Center both eyes on one visual field –Produce a clear image on the retina

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18 Intrinsic Muscles – found in two structures within the eye 1. 1.Iris ––C––Color part of the eye ––C––Contains the pupil ––R––Regulates the amount of light entering the eye ––M––Muscles of the iris will reduce or CONSTRICT the size of the pupil in bright light ––M––Muscles of the iris will expand or DILATE the size of the pupil in dim light

Ciliary Muscle Alters the shape of the lens during the process of ACCOMMODATION Accommodation involves coordinated eye changes to enable a person to focus on near objects

20 The Optic Nerve Carries visual impulses from the rods and cones to the brain Carries visual impulses from the rods and cones to the brain

21 Eye Disorders Hyperopia – Farsightedness Usually due to an abnormally short eyeball Focal point is BEHIND the retina Light rays cannot bend sharply enough to focus ON the retina Objects must be moved AWAY from the eye to be seen clearly Corrected with a CONVEX lens

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Nearsightedness 2. Myopia - Nearsightedness Eyeball is too long Eyeball is too long Cornea bends light too sharply Cornea bends light too sharply Focal point is in FRONT of the retina Focal point is in FRONT of the retina Distant objects appear blurry and must be moved TOWARD the eye to be seen clearly Distant objects appear blurry and must be moved TOWARD the eye to be seen clearly Corrected with a CONCAVE lens Corrected with a CONCAVE lens

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Astigmatism An irregularity in the curvature of the cornea or the lens An irregularity in the curvature of the cornea or the lens Light rays are incorrectly bent, causing blurred vision Light rays are incorrectly bent, causing blurred vision Usually found in combination with hyperopia or myopia Usually found in combination with hyperopia or myopia

28 Eye Infections Conjunctivitis – “Pink Eye” Conjunctivitis – “Pink Eye” –Inflammation of the membrane that lines the eyelid –Highly contagious –Causes may include:  Irritants (wind,glare)  Bacterial Infections

29 Inclusion Conjunctivitis Acute infection caused by “chlamydia trachomatis” (also causes the STD Acute infection caused by “chlamydia trachomatis” (also causes the STD History of sexual activity and previous sexually transmitted disease is important History of sexual activity and previous sexually transmitted disease is important Causes scarring of cornea & blindness Causes scarring of cornea & blindness

30 Eye Injuries Scratched Cornea –Caused by foreign objects or infection –Scarring results; light cannot pass through –Blindness may result

31 Cataracts Covering of the lens Covering of the lens Can cause gradual loss of vision or complete loss Can cause gradual loss of vision or complete loss Age is a factor Age is a factor Surgery can restore vision Surgery can restore vision

32 Glaucoma Excess pressure on the aqueous humor Excess pressure on the aqueous humor Progresses slowly Progresses slowly Early diagnosis can result in preserving vision Early diagnosis can result in preserving vision

33 Retinal Detachment Retina separates from the rest of the eye Retina separates from the rest of the eye Can result from head trauma Can result from head trauma Left untreated can cause blindness Left untreated can cause blindness

34 Macular Degeneration Changes in part of the retina that can distort vision & cause blindness Changes in part of the retina that can distort vision & cause blindness Factors: Factors: –Smoking –Sunlight –High cholesterol diet

35 The Ear Sensory organ for both hearing and equilibrium Sensory organ for both hearing and equilibrium : Divided into three main sections: – –Outer Ear – includes the ear canal – –Middle Ear – air space including 3 small bones (hammer, anvil & stirrup) – –Inner Ear – most complex area and contains the receptors for hearing & equilibrium

36 The Eustachian Tube The “auditory tube” Connects the middle ear with the pharynx (throat) of the Opens to allow pressure to equalize on both sides of the TYMPANIC MEMBRANE (eardrum)

37 Disorders of the Ear or ear infection of the middle ear “Otitis Media” or ear infection of the middle ear Relatively common Relatively common Caused by a variety of bacteria & viruses Caused by a variety of bacteria & viruses Frequently a complication of measles & flu Frequently a complication of measles & flu

38 Hearing Loss Deafness is a complete loss of hearing Deafness is a complete loss of hearing hearing loss CONDUCTIVE hearing loss –Due to interference with the passage of sound waves from the outer to inner ear by an OBSTRUCTION (wax or a foreign body)

39 Sensorineural Hearing Loss Due to prolonged exposure to loud noises, use of certain drugs for long periods of time or exposure to infection or toxins Due to prolonged exposure to loud noises, use of certain drugs for long periods of time or exposure to infection or toxins

40 Taste Receptors found in the tongue Receptors found in the tongue Two nerves carry taste impulses to the brain Two nerves carry taste impulses to the brain Receptors (taste buds) are stimulated when saliva mixes with a substance Receptors (taste buds) are stimulated when saliva mixes with a substance

41 Taste Experiences Sweet – at the TIP Sweet – at the TIP Sour – at the SIDES Sour – at the SIDES Salty – on the top portion of the side of the tongue Salty – on the top portion of the side of the tongue Bitter – at the BACK Bitter – at the BACK

42 Smell Impulses are carried by the OLFACTORY nerve to the brain Olfactory receptors deteriorate with age Closely related to taste & is important in stimulating appetite & flow of digestive juices

43 General Senses Touch – –Receptors found in dermis of skin and hair follicles – –Sensitivity varies with number of receptors

44 Pressure Pressure –Receptors found in most deep tissue and joints

45 Temperature Temperature –Receptors widely distributed in skin –Separate receptors for heat and cold

46 Position Position –Receptors found in muscles, tendons & joints –Aid in judging position & location of body parts in relation to each other –Inform the brain of the proper amount of muscle contraction and tendon tension

47 Pain Pain –Receptors widely distributed –Found in the skin, muscles, joints and most internal organs