1. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Chapter 25 The Senses

2. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Senses of the Human Body and Corresponding Organs Sight: the eye Hearing: the ear Taste: the tongue Smell: the nose Touch: the skin Knowledge of the environment requires sensory organs, cranial nerves, and the brain to interpret stimuli. Copyright ©2012 Delmar, Cengage Learning. All rights reserved.

3. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Structures of the Eye

4. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Structures of the Eye Sclera: tough outer covering – Maintains the shape of the eye Extraocular muscles (6) – Contract or relax to permit movement of the eyeball Choroid – Layer under the sclera – Contains the blood vessels that serve the eye tissues – This layer also has a nonreflective pigment that keeps light from reflecting within the eye.

5. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Structures of the Eye Retina: focuses an image onto the surface Iris: colored circular muscle that surrounds the pupil; regulates the amount of light Optic disk: blind spot Pupil: central opening Cornea: curved covering of the sclera that can correct some unclear images

6. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Structures of the Eye Conjunctiva: the white of the eye Vitreous humor: thick, jellylike substance that maintains the shape of the eyeball Aqueous humor: salty clear fluid; circulates between the chambers

7. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Structures of the Eye Fovea centralis: posterior surface of the retina; the area of sharpest vision Rods: nerve cells that transmit the stimuli so we can see in black and white Cones: nerve cells that transmit the stimuli so we can see in color

8. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Effects of the Lens and Cornea on Focusing Images When the lens or cornea has an abnormal curvature, the image is improperly refracted. When the image is focused in front of the retina, the person is said to nearsighted. The medical term for nearsightedness is myopia.

9. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Effects of the Lens and Cornea on Focusing Images When the image is focused behind the retina, the person is said to be farsighted. The medical term for farsightedness is hyperopia.

10. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Age-Related Macular Degeneration A disease that affects the most sensitive part of the retina, and alters the center of the visual field Results in a gradual loss of central vision, but side vision is maintained

11. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Amblyopia Also called lazy eye Most often affects children under age 5 One eye turns inward, causing blurred vision

12. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Arcus Senilis Accompanies normal aging Results in a thin greyish-white arc or circle not quite at the edge of the cornea

13. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Blepharitis Inflammation of the edges of the eyelids involving the hair follicle and glands Results in itching and burning, rubbing eyes, and constant blinking

14. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Cataract Gradually developing opacity of the lens Occurs most frequently in persons over the age of 70 Causes painless, gradual blurring and loss of vision

15. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Conjunctivitis Caused by inflammation of the conjunctiva Begins in one eye and spreads to the other; causes redness and a “bloodshot” appearance Usually caused by a bacterial infection

16. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Corneal Abrasion A scratch or trauma to the cornea usually caused by a foreign body in the eye Vision can be affected if the location and extent of the injury are significant

17. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Diabetic Retinopathy Usually results from juvenile or adult diabetes Edema of the retina causes light to scatter Capillary walls dilate, twist, and/or hemorrhage Causes glare, blurred vision, and reduced visual acuity

18. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Characterized by excessive intraocular pressure that results in atrophy of the optic nerve; causes severe visual impairment and eventual blindness Glaucoma

19. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Diseases of the Eye Closed-angle glaucoma – Aqueous humor cannot drain because of a blockage and pressure rises slowly Acute closed-angle glaucoma – Obstruction of the drainage holes resulting from automatically shallow chambers and a thickened iris that closes the passages – There is a rapid onset of symptoms; this is considered an emergency.

20. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Hordeolum and Iritis Hordeolum – Localized infection of the gland of the eyelid; produces an abscess around an eyelash – Causes red, painful, and swollen eyes Iritis – Inflammation of the iris; causes moderate to severe eye pain, sensitivity to light, and small, nonreactive pupils

21. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Presbyopia and Ptosis Presbyopia – Inability of the lens to accommodate for near vision; usually occurs as a normal part of the aging process Ptosis – Drooping of the upper eyelid that results in the eyes appearing to be only partially open – Could be the result of a congenital condition, aging, excess fatty folds, or neurological factors

22. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Retinal Detachment Results from separation of the retina from the choroid layer of the eyeball Causes the patient to see floating spots, flashes of light, and a gradual loss of vision

23. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Strabismus One eye deviates with the gaze being abnormally inward or outward or higher or lower than the other eye This can results in: – Esotropia: abnormally inward gaze – Exotropia: abnormally outward gaze

24. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Structures of the Ear

25. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Structures of the Ear Pinna: external ear shell; also called the auricle; collects and directs sound down the external auditory canal External auditory canal: passageway from outside to the eardrum Tympanic membrane: eardrum; vibrates when sound waves hit it

26. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Structures of the Ear Vibrations from the tympanic membrane hit the three small bones of the middle ear. The malleus (hammer) strikes the incus (anvil), which moves the stapes (stirrups). This communicates the vibrations to the inner ear when the stapes pushes against the fluid in the vestibule of the inner ear.

27. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Structures of the Ear The middle ear is connected by the eustachian tube to the throat. The eustachian tube equalizes the air pressure in the middle ear with the outside air pressure.

28. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Structures of the Ear Vibrations from the middle ear continue through a snail-shaped organ called the cochlea. The cochlea contains a collection of specialized nerve cells called the organ of Corti.

29. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Structures of the Ear The organ of Corti transmits impulses to the auditory nerve, which passes them on to the auditory center of the temporal lobe of the cerebrum of the brain for interpretation. The inner ear also contains three semicircular canals that are responsible for maintaining balance.

30. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Balance Function of the Inner Ear Hairlike nerve cells within the three canals are embedded in a gelatin-like material that pushes against receptors when the head moves and transmits this change in position to the brain.

31. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Auditory canal obstruction Anything in the ear canal that can occlude the opening

32. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Hearing Loss Reduced ability to perceive sound at normal levels Hearing loss can be the result of obstruction, nerve damage from prolonged exposure to noise, or disease

33. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Meniere’s Disease Disorder of the inner ear that usually affects only one ear; typically begins between ages 20 and 50 Results in extreme dizziness (vertigo) and ringing in the ears (tinnitus).

34. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Motion Sickness Loss of balance, perspiration, headache, nausea, and vomiting brought on by irregular motion Examples: riding in cars, boats, planes, or amusement park rides

35. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Otitis Otitis externa – Infection of the external auditory canal that causes pain and hearing loss Otitis media – Infection of the middle ear often associated with respiratory infections

36. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Otosclerosis and Prebycusis Otosclerosis – Loss of movement of the stapes that results in deafness called bone conduction deafness Presbycusis – Progressive hearing loss that usually results as a result of aging

37. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Epistaxis and Nasal Polyps Epistaxis – Bleeding from the nose that can result from trauma or a disease process Nasal polyps – Benign growths inside the nose that obstruct the airway

38. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Rhinitis A reaction to airborne allergens that results in sneezing, watery eyes, and itching of the eyes and nose

39. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Structures of the Nose The sense of smell is caused by the olfactory organ in the top of the nasal cavity. Nerve fibers in the nose respond to stimuli and these nerve fibers run through tiny holes in the skull to the olfactory center in the brain.

40. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Structures of the Tongue The ability to taste flavors is located in the receptors of the taste buds on the tongue. These receptors are located at the tip, sides, and back of the tongue.

41. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Taste Sensation and the Corresponding Areas of the Tongue Tip – Sweet Sides – Sour Back – Bitter Area between tip and sides – Salty

42. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Candidiasis Fungal infection of the mouth and throat that results in white patches that appear on the tongue, mouth, or throat

43. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Glossitis and Oral Cancer Glossitis – Inflammation of the tongue Oral cancer – Cancer of the tongue, mouth, or throat; often linked to tobacco use

44. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Structures of the Skin Touch receptors are located in the fingertips. Pain receptors are bare nerve endings in the skin and other organs. Skin receptors perceive heat and cold.

45. Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Skin’s Contact Receptors The sense of touch involves pressure or traction that activates mechanoreceptors. Radiant energy, heat or cold, activates thermoreceptors.