1 CHAPTER 20 SENSORY SYSTEMAccommodation Auditory Converge Cutaneous Equilibrium Gustatory Intraocular Labyrinth Olfactory Receptor Refraction Stimulus Vision Journal question: What are the six senses?

2 Chapter 20 Learning ObjectivesDefine 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 Chapter 20 Learning ObjectivesIdentify at least three methods of assessment of the sensory system. Describe at least five disorders of the sensory system.

4 Structure and FunctionThe 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. Discuss the term receptors. Discuss the term stimuli.

5 Structure and FunctionEnvironmental stimuli are perceived by means of Vision Hearing Touch Taste Position Balance Taste is the weakest of the senses.

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. The human eye can process 36,000 bits of information every hour. Explain extrinsic muscles. Blinking one eye involves the movement of 200 muscles.

7 Eye The eyeball is not solid.Divided into cavities (anterior and posterior) Anterior filled with aqueous humor Posterior filled with vitreous humor 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. The iris is the colored part of the eye. What color is the pupil of the eye? Eyeballs are 3.5% salt.

8 Structure of the Eye Discuss each structure of the eye and its location, and give brief description of its function. FIGURE 20-1 Structures of the eye. (From Sorrentino SA: Mosby’s textbook for nursing assistants, ed 7, St. Louis, 2008, Mosby.)

9 Eye Vision is similar to the action of a camera. RefractionLens bends light rays as they enter the eye to focus on the retina. Accommodation The lens changes shape to focus near and far. Converge Single binocular vision occurs, and only one object is seen. Refer to Slide 11 or Figure 20-2 in the students’ textbook for this discussion.

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 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. In the middle of the day, eyesight is sharper. It is impossible to sneeze with your eyes open.

11 The Eye Functions Like a CameraFIGURE 20-2 The eye functions like a camera.

12 Ear Main functions of the ear Three main parts of the earAuditory 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 Men listen with the left side of the brain and women use both sides of the brain.

13 Parts of the Ear External ear The shape channels incoming sound wavesSpecialized glands in the ear canal produce cerumen, which protects the middle ear.

14 Parts of the Ear Middle ear Air-filled chamberTympanic membrane changes sound waves into mechanical movements. Auditory bones transmit sound vibrations. 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 The Eustachian tube can become blocked so that external and internal pressure become imbalanced. This can be caused by the mucous secretions of a cold or enlarged adenoids.

15 Parts of the Ear Inner earContains 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. 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. The inner ear is the main organ of balance.

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. Every person has a unique tongue print. Most people have lost 50% of their taste buds by the time they turn 50. Locate the papillae on Figure 20-4 in students’ textbook or the next slide.

18 Taste Buds The life span of a taste bud is 5 days.FIGURE 20-4 Taste buds are located on the tongue. (From Patton KT, Thibodeau GA: Anatomy & physiology, ed 7, St. Louis, 2010, Mosby.)

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. The human nose can remember 50,000 different smells. Women have a better sense of smell than men. About 2 million people in the United States have no sense of smell.

20 Nose Smells can Reduce stress Affect blood pressure Recall memoriesAid the sense of taste The sense of smell is 10,000 times more sensitive than taste. About 2 million people in the United States have no sense of smell.

22 Skin The skin can sense touch, pressure, temperature, and pain through five specialized cells: Meissner's corpuscles Sense light touch and motion Pacinian corpuscles Sense deep pressure End-bulbs of Krause Sense cold, low-frequency vibrations, two-point discrimination There are 45 miles of nerves in the skin of a human being.

23 Skin Corpuscles of Ruffini NociceptorsSense heat, deep pressure, and continuous touch Nociceptors Pain receptors Respond to more than one stimulus The brain has no pain receptors. Pain is the only type of nerve receptor found in visceral organs.

24 Nerve Receptors of the SkinHave students identify the functions of each of the nerve receptors of the skin in Figure 20-6. 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 Assessment TechniquesSight 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 Color blind people find it hard to distinguish colors such as green and red.

26 Assessment TechniquesHearing 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 Discuss each of the assessment techniques used for testing hearing.

30 Disorders of the Sensory SystemAchromatism 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 Discuss the signs, symptoms, and treatment of each of these disorders. Color blindness affects 1 in 30 people.

31 Disorders of the Sensory SystemAstigmatism 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. Discuss the signs, symptoms, and treatment of each of these disorders.

33 Disorders of the Sensory SystemDeafness 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 Discuss the signs, symptoms, and treatment of each of these disorders.

35 Disorders of the Sensory SystemDiplopia 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 Discuss the signs, symptoms, and treatment of each of these disorders.

36 Disorders of the Sensory SystemHyperopia Farsightedness resulting from a congenital deformity in the eye Macular degeneration Slow or sudden, painless loss of central vision Discuss the signs, symptoms, and treatment of each of these disorders.

37 Disorders of the Sensory SystemMénière'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 Discuss the signs, symptoms, and treatment of each of these disorders.

38 Disorders of the Sensory SystemOtitis 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 Discuss the signs, symptoms, and treatment of each of these disorders.

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 Disorders of the Sensory SystemRhinitis 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) Discuss the signs, symptoms, and treatment of each of these disorders.

41 Disorders of the Sensory SystemStrabismus Condition in which both eyes do not focus on the same point or direction Stye Bacterial infection of the sebaceous glands of the eyelid Discuss the signs, symptoms, and treatment of each of these disorders.

42 Issues and InnovationsVisual correction by surgery Radial keratotomy (microscopic surgery) Epikeratophakia Intacs (intracorneal rings) Photorefractive keratectomy (PRK) (laser surgery) Noise pollution Inner ear damage is permanent. Loud music and phones can cause hearing loss.

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 Summary Methods of assessment of the sensory system Snellen chartOtoscope Rinne test

45 Summary Disorders of the sensory system Conjunctivitis EpistaxisGlaucoma Macular degeneration Rhinitis

46 Review The term olfactory, with regard to the sensory system, pertains to: a. Taste b. The sense of smell c. Inflammation of the eardrum d. Disease of the retina e. The sense of movement

47 Review The term olfactory, with regard to the sensory system, pertains to: a. Taste b. The sense of smell c. Inflammation of the eardrum d. Disease of the retina e. The sense of movement

48 Review Tympanitis, with regard to the sensory system, is: a. Tasteb. The sense of smell c. Inflammation of the eardrum d. Disease of the retina e. The sense of movement

49 Review Tympanitis, with regard to the sensory system, is: a. Tasteb. The sense of smell c. Inflammation of the eardrum d. Disease of the retina e. The sense of movement

50 Review Amblyopia, a disorder of the sensory system, is: a. A nosebleed that results from disease, trauma, or other conditions, such as hypertension, leukemia, or rheumatic fever b. A clouding of the lens that causes blurred or partial vision c. Poor vision in one eye, often resulting from better vision in the other eye during infancy or childhood d. A slow or sudden painless loss of central vision e. A collection of fluid in the labyrinth of the ear, leading to dizziness, ringing in the ear, or tinnitus pressure and eventual deafness

51 Review Amblyopia, a disorder of the sensory system, is: a. A nosebleed that results from disease, trauma, or other conditions, such as hypertension, leukemia, or rheumatic fever b. A clouding of the lens that causes blurred or partial vision c. Poor vision in one eye, often resulting from better vision in the other eye during infancy or childhood d. A slow or sudden painless loss of central vision e. A collection of fluid in the labyrinth of the ear, leading to dizziness, ringing in the ear, or tinnitus pressure and eventual deafness

52 Review Epistaxis, a disorder of the sensory system, is:a. A nosebleed that results from disease, trauma, or other conditions, such as hypertension, leukemia, or rheumatic fever b. A clouding of the lens that causes blurred or partial vision c. Poor vision in one eye, often resulting from better vision in the other eye during infancy or childhood d. A slow or sudden painless loss of central vision e. A collection of fluid in the labyrinth of the ear, leading to dizziness, ringing in the ear, or tinnitus pressure and eventual deafness

53 Review Epistaxis, a disorder of the sensory system, is:a. A nosebleed that results from disease, trauma, or other conditions, such as hypertension, leukemia, or rheumatic fever b. A clouding of the lens that causes blurred or partial vision c. Poor vision in one eye, often resulting from better vision in the other eye during infancy or childhood d. A slow or sudden painless loss of central vision e. A collection of fluid in the labyrinth of the ear, leading to dizziness, ringing in the ear, or tinnitus pressure and eventual deafness