1. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.1 CHAPTER 20 SENSORY SYSTEM

2. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.2 Chapter 20 Learning Objectives  Define at least 10 terms relating to the sensory system.  Describe the function of the sensory system.  Identify at least 10 sensory system structures and the function of each.

3. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.3 Chapter 20 Learning Objectives  Identify at least three methods of assessment of the sensory system.  Describe at least five disorders of the sensory system.

4. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.4 Structure and Function  The sensory system consists of receptors in specialized cells and organs that perceive changes in the internal and external environment.  Stimuli generate nerve impulses that are sent to the brain for interpretation.

5. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.5 Structure and Function  Environmental stimuli are perceived by means of  Vision  Hearing  Touch  Taste  Position  Balance

6. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.6 Eye  The eye is most important sensory organ, because 90% of the information about the environment reaches the brain from the eyes.  Movement of the eye is controlled by the extrinsic muscles.  Only one fifth of the eye is exposed to the environment.

7. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.7 Eye  The eyeball is not solid.  Divided into cavities (anterior and posterior) Anterior filled with aqueous humor Anterior filled with aqueous humor Posterior filled with vitreous humor Posterior filled with vitreous humor Aqueous and vitreous humors help maintain shape of the eye Aqueous and vitreous humors help maintain shape of the eye  Iris is a round, colored muscle that adjusts the amount of light entering the eye.  Lens is a convex, transparent tissue that focuses and directs incoming light on the retina of the eye.

8. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.8 Structure of the Eye FIGURE 20-1 Structures of the eye. (From Sorrentino SA: Mosby’s textbook for nursing assistants, ed 7, St. Louis, 2008, Mosby.)

9. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.9 Eye  Vision is similar to the action of a camera.  Refraction Lens bends light rays as they enter the eye to focus on the retina. Lens bends light rays as they enter the eye to focus on the retina.  Accommodation The lens changes shape to focus near and far. The lens changes shape to focus near and far.  Converge Single binocular vision occurs, and only one object is seen. Single binocular vision occurs, and only one object is seen.

10. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.10 Eye  Rods and cones are specialized cells in the retina that absorb light.  Rods are sensitive to dim light.  Cones React to bright light React to bright light Allow color distinction through three types of pigments that recognize primary colors Allow color distinction through three types of pigments that recognize primary colors  Impulses released by pigments in rods and cones are transmitted to the brain by the optic nerve.

11. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.11 The Eye Functions Like a Camera FIGURE 20-2 The eye functions like a camera.

12. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.12 Ear  Main functions of the ear  Auditory or acoustic sense (hearing) is the primary function of the ear.  Hearing helps to maintain equilibrium.  Three main parts of the ear  External  Middle  Inner

13. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.13 Parts of the Ear  External ear  The shape channels incoming sound waves  Specialized glands in the ear canal produce cerumen, which protects the middle ear.

14. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.14 Parts of the Ear  Middle ear  Air-filled chamber Tympanic membrane changes sound waves into mechanical movements. Tympanic membrane changes sound waves into mechanical movements. Auditory bones transmit sound vibrations. Auditory bones transmit sound vibrations. Ossicles amplify and transmit sound to the inner ear. Ossicles amplify and transmit sound to the inner ear.  Eustachian tube allows pressure of air in the middle ear to be equalized with the air pressure of the environment

15. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.15 Parts of the Ear  Inner ear  Contains a series of canals called the bony labyrinth. Movement of fluid and hair cells lining the cochlea converts the mechanical vibration from the ossicles to neural impulses. Movement of fluid and hair cells lining the cochlea converts the mechanical vibration from the ossicles to neural impulses. Semicircular canals contain endolymph that gives a sense of balance when body is in motion. Semicircular canals contain endolymph that gives a sense of balance when body is in motion. Vestibule has two chambers (saccule and utricle) that maintain resting equilibrium. Vestibule has two chambers (saccule and utricle) that maintain resting equilibrium.

16. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.16 Structure of the Ear FIGURE 20-3 Structures of the ear.

17. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.17 Tongue  Taste, or the gustatory sense, is perceived by specialized cells located in papillae on the tongue called taste buds.  Five tastes are perceived by all areas of the tongue.  Sweet, sour, bitter, salty, and umami (meatiness)  Flavor is identified by smell and taste.

18. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.18 Taste Buds FIGURE 20-4 Taste buds are located on the tongue. (From Patton KT, Thibodeau GA: Anatomy & physiology, ed 7, St. Louis, 2010, Mosby.)

19. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.19 Nose  Olfactory sense originates in olfactory receptor cells in the nose that immediately transmit impulses to the brain through the olfactory cranial nerves.  The nasal cavity is divided into two sections by the septum.  Olfactory receptor neurons are stimulated by chemicals (gases) in the air.

20. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.20 Nose  Smells can  Reduce stress  Affect blood pressure  Recall memories  Aid the sense of taste

21. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.21 Nose and Surrounding Structure FIGURE 20-5 The nose and surrounding structures.

22. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.22 Skin  The skin can sense touch, pressure, temperature, and pain through five specialized cells:  Meissner's corpuscles Sense light touch and motion Sense light touch and motion  Pacinian corpuscles Sense deep pressure Sense deep pressure  End-bulbs of Krause Sense cold, low-frequency vibrations, two-point discrimination Sense cold, low-frequency vibrations, two-point discrimination

23. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.23 Skin  Corpuscles of Ruffini Sense heat, deep pressure, and continuous touch Sense heat, deep pressure, and continuous touch  Nociceptors Pain receptors Pain receptors Respond to more than one stimulus Respond to more than one stimulus

24. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.24 Nerve Receptors of the Skin FIGURE 20-6 Nerve receptors of the skin. A, Meissner’s corpuscle (touch). B, Pacinian corpuscle (pressure). C, Krause’s end-bulb. D, Ruffini nerve endings (warmth). E, Free nerve endings (pain).

25. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.25 Assessment Techniques  Sight  Ophthalmoscope to examine inner structure of the eye  Visual acuity with the Snellen test  Tonometer to measure pressure of the inner eye  Color blindness chart to identify defects in color determination

26. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.26 Assessment Techniques  Hearing  Otoscope to view the structures of ear  Audiometer to measure hearing ability  Impedance testing to measure flexibility of the tympanic membrane  Rinne’s test using a tuning fork to assess transmission of sound through the ear structure  Weber's test using tuning fork to test for unilateral or one-sided hearing loss

27. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.27 Hearing Aid FIGURE 20-9 Hearing Aid. (Courtesy Siemens Hearing Instruments, Inc., Piscataway, NJ. In Sorrentino SA: Mosby’s textbook for nursing assistants, ed 7, St. Louis, 2008, Mosby.)

28. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.28 Eye Examination FIGURE 20-7 Eye examination. A, Ophthalmoscope.

29. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.29 Ophthalmoscopic View of the Retina FIGURE 20-7 Eye examination. B, Retina.

30. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.30 Disorders of the Sensory System  Achromatism  Also called color blindness, it is a common inherited defect.  Amblyopia  Also called lazy eye, it is poor vision in one eye often resulting from better vision in the other eye during infancy or early childhood.  Anacusis  Hearing loss resulting from damage to neural tissues

31. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.31 Disorders of the Sensory System  Astigmatism  Congenital defect causing imperfect curvature of the cornea and resulting in blurred vision  Cataract  Clouding of the lens that causes blurred or partial vision  Conjunctivitis  Also called pink eye, it is a bacterial or viral inflammation of the eyelid.

32. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.32 Cataracts FIGURE 20-10 Cataracts cause blurred or partial vision. (From Patton KT, Thibodeau GA: Anatomy & physiology, ed 7, St. Louis, 2010, Mosby.)

33. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.33 Disorders of the Sensory System  Deafness  Complete loss of hearing in one or both ears  Inherited or caused by complications at birth, disease, excessive noise, or ototoxic drugs  Diabetic retinopathy  Condition of damaged blood vessels in the retina caused by uncontrolled diabetes mellitus

34. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.34 Cochlear Implant FIGURE 20-11 Cochlear implant. (Courtesy of Stephanie Freese, artist, and American Scientist, The Magazine of Sigma Xi, The Scientific Research Society. In Gould BE, Dyer R: Pathophysiology for the health professions, ed 4, St. Louis, 2011, Saunders.)

35. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.35 Disorders of the Sensory System  Diplopia  Also called double vision, it results from muscle imbalance or paralysis of an extraocular muscle.  Epistaxis  Nosebleed resulting from disease, trauma, or other conditions such as hypertension, leukemia, or rheumatic fever  Glaucoma  Increased pressure inside the eye caused by trauma or hereditary factors

36. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.36 Disorders of the Sensory System  Hyperopia  Farsightedness resulting from a congenital deformity in the eye  Macular degeneration  Slow or sudden, painless loss of central vision

37. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.37 Disorders of the Sensory System  Ménière's disease  Collection of fluid in the labyrinth of the ear leading to dizziness, ringing in the ear (tinnitus), pressure, and eventual deafness  Myopia  Nearsightedness resulting from a congenital deformity in the eye  Night blindness  Poor vision in dim light that results from a deficiency in the rods of the retina

38. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.38 Disorders of the Sensory System  Otitis media  Middle ear bacterial or viral infection common in young children  Presbyopia  Type of farsightedness related to aging  Retinal detachment  Result of injury or uncontrolled diabetes mellitus

39. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.39 Otitis Media FIGURE 20-12 Otitis media is a common among young children. (From Damjanov I: Pathology for the health professions, ed 3, St. Louis, 2006, Saunders.)

40. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.40 Disorders of the Sensory System  Rhinitis  Inflammation of the lining of the nose caused by allergic reaction, viral infection, sinusitis, or chemical irritants  Ruptured eardrum  Results from infection, an explosion, a blow to the head, or a sharp object inserted into the ear  Sinusitis  Chronic or acute inflammation of a sinus (usually paranasal)

41. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.41 Disorders of the Sensory System  Strabismus  Condition in which both eyes do not focus on the same point or direction  Stye  Bacterial infection of the sebaceous glands of the eyelid

42. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.42 Issues and Innovations  Visual correction by surgery  Radial keratotomy (microscopic surgery)  Epikeratophakia Intacs (intracorneal rings) Intacs (intracorneal rings)  Photorefractive keratectomy (PRK) (laser surgery) Intacs (intracorneal rings) Intacs (intracorneal rings)  Noise pollution  Inner ear damage is permanent.  Loud music and phones can cause hearing loss.

43. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.43 Summary  The function of the sensory system is to perceive changes in the internal and external environment with specialized receptors.  Sensory system structures  Eye  Ear  Tongue  Nose  Skin

44. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.44 Summary  Methods of assessment of the sensory system  Snellen chart  Otoscope  Rinne test

45. Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.45 Summary  Disorders of the sensory system  Conjunctivitis  Epistaxis  Glaucoma  Macular degeneration  Rhinitis