Copyright © 2005, Elsevier, Inc. All rights reserved. Slide 0 0 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Chapter 9 The Senses

1 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Learning Objectives Classify sense organs as special or general and explain the basic differences between the two groups Discuss how a stimulus is converted into a sensation Discuss the general sense organs and their functions

2 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Learning Objectives (cont’d.) Describe the structure of the eye and the functions of its components Discuss the anatomy of the ear and its sensory function in hearing and equilibrium Discuss the chemical receptors and their functions

3 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question There are two major types of sense organs. What are they?

4 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Classification of the Sense Organs General sense organs  Often exist as individual cells or receptor units  Widely distributed throughout the body Special sense organs  Large and complex organs  Localized grouping of specialized receptors

5 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Classification of the Sense Organs (cont’d.) Classified by presence or absence of covering capsule  Encapsulated  Unencapsulated (“free” or “naked”)

6 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question What are the some of the types of stimuli needed to activate sensory receptors?

7 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Classification made by type of stimuli required to activate receptors  Photoreceptors (light)  Chemoreceptors (chemicals)  Pain receptors (injury)  Thermoreceptors (temperature changes)  Mechanoreceptors (movement or deforming of capsule)  Proprioceptors (position of body parts or changes in muscle length or tension) Classification of the Sense Organs (cont’d.)

8 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Converting a Stimulus into a Sensation All sense organs have common functional characteristics  All are able to detect a particular stimulus  A stimulus is converted into a nerve impulse  A nerve is perceived as a sensation in the CNS

9 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. General Sense Organs Distribution is widespread; single-cell receptors are common Examples  Free nerve endings: Sensitive to pain and crude touch  Meissner’s corpuscles: Responsive to fine touch and vibration  Ruffini’s corpuscles: Sensitive to touch and pressure  Krause’s end-bulbs: Touch or cold  Golgi tendon receptors: Proprioception  Muscle spindles: Proprioception

10 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

11 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Special Sense Organs There are four types of special sense organs in the body. What are they?

12 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Special Sense Organs The eyeball  Three layers of the eyeball  Sclera  Choroid  Retina

13 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

14 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Special Sense Organs (cont’d.)  Conjunctiva: Mucous membrane covering the front surface of the sclera and lining the eyelid  Lens: Transparent body behind the pupil; focuses light rays on the retina  Eye fluids  Aqueous humor: Watery fluid in the anterior chamber in front of the lens  Vitreous humor: Jellylike fluid in the posterior chamber behind the lens

15 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Special Sense Organs (cont’d.)  Visual pathway  Innermost layer of retina contains rods and cones  Impulse travels from the rods and cones through the bipolar and ganglionic layers of retina  Nerve impulse leaves the eye through the optic nerve; the point of exit is free of receptors and is therefore called a blind spot  Visual interpretation occurs in the visual cortex of the cerebrum

16 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

17 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question How does the iris changes the size of the pupil?

18 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer As the fibers of the iris contract, the pupils dilate, letting in more light. Other fibers are circular. When they contract, the pupils constrict, letting in fewer light rays. Normally the pupils constrict in bright light and dilate in dim light.

19 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question What is presbyopia, and what is its cause?

20 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer Presbyopia is farsightedness.

21 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question What are cataracts?

22 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer It is a condition in which the lens of the eye becomes hard and loses transparency, taking on a milky appearance.

23 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

24 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question Where is the blind spot, and what causes it?

25 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer An impulse travels through the optic nerve. The point of exit from the retina has no receptors and is therefore called the blind spot.

26 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Special Sense Organs (cont’d.) The ear  The ear functions in hearing, equilibrium, and balance.  Receptors for hearing and equilibrium are mechanoreceptors.

27 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Special Sense Organs (cont’d.)  Divisions of the ear  External ear o Auricle (pinna) o External auditory canal Curving canal or tube 2.5 cm (1 inch) in length Contains ceruminous glands producing ear wax Ends at the tympanic membrane or eardrum

28 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

29 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Special Sense Organs (cont’d.)  Middle ear o Houses ear bones or ossicles—malleus, incus, and stapes o Ends in the oval window o The auditory (eustachian) tube connects the middle ear to the throat o Inflammation called “otitis media”

30 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Special Sense Organs (cont’d.)  Inner ear o The bony labyrinth is filled with fluid called perilymph o The labyrinth is divided into the vestibule, semicircular canals, and cochlea o Membranous labyrinth is filled with endolymph o Receptors for balance in the semicircular canals are called cristae ampullaris o Specialized hair cells on the organ of Corti respond when bent by the movement of surrounding endolymph set in motion by sound waves

31 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

32 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

33 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question What are the names of the two structures of the external ear?

34 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer (1)the auricle is the appendage on the side of the head surrounding the opening of the external auditory canal. (2)the external auditory canal is a curved tube that extends into the temporal bone and ends at the tympanic membrane.

35 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question What are the names of the three ossicles that allow sound to be transmitted through the middle ear?

36 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer The names of the bones describe their shape: 1. The malleus (hammer), 2. The incus (anvil), 3. The stapes (stirrup).

37 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question How does the structures in the inner ear help maintain balance or equilibrium?

38 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer The inner ear (also called labyrinth) contains the semicircular canals and the cochlea. The semicircular canals are filled with endolymph and are the primary organs in maintaining balance and equilibrium. Damage or disease to this part of the ear not only affects balance but also may result in permanent hearing loss.

39 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Special Sense Organs (cont’d.) The taste receptors  Receptors are chemoreceptors called taste buds  Cranial nerves VII and IX carry gustatory impulses  Six kinds of “primary” taste sensations—sweet, sour, bitter, salty, metallic, and umami (meaty)  Gustatory and olfactory senses work together

40 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

41 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question Where are gustatory cells located and to what four tastes do they respond?

42 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer Gustatory cells are taste buds! There are four kinds of taste sensations: 1.Sweet 2.Sour 3.Bitter 4.Salty

43 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Special Sense Organs (cont’d.) The olfactory (smell) receptors  Receptors for fibers of olfactory or cranial nerve lie in olfactory mucosa of nasal cavity  Olfactory receptors are extremely sensitive but easily fatigued  Odor-causing chemicals initiate a nervous signal that is interpreted as a specific odor by the brain

44 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

45 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question How is the sense of smell stimulated?

46 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer The chemoreceptors (olfactory receptors) responsible for the sense of smell are located in a small area of epithelial tissue in the upper part of the nasal cavity. Each olfactory cell has a number of specialized cilia that sense different chemicals and cause the cell to respond by generating a nervous impulse. To be detected by olfactory receptors, chemicals must be dissolved in the watery mucus that lines the nasal cavity.

Copyright © 2005, Elsevier, Inc. All rights reserved. Slide Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Let’s Review! Chapter 9

48 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Slide 48 Which of these is special sense? A.Pressure B.Stretch C.Vision D.Temperature E.Pain

49 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Slide 49 A mechanoreceptor may detect changes in A.Temperature B.Light intensity C.pH D.Pressure E.Presence of sugars

50 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Slide 50 Muscle spindles are involved in the sense of A.Proprioception B.Pain C.Smell D.Movement E.Gravity

51 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Slide 51 Color vision relies on the function of A.Rods B.Cones

52 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Slide 52 The organ of Corti is involved in the sense of A.Vision B.Pain C.Hearing D.Equilibrium E.Motion

53 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Slide 53 Sensory perception occurs in the A.Receptor B.Organ surrounding the receptor C.Afferent neuron D.Brain

54 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question Why does food lose some of its taste when you have a bad cold with a stuffy nose?

55 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer All flavors result from a combination of taste bud and olfactory receptor stimulation. For this reason, a cold that interferes with the stimulation of the olfactory receptors markedly dulls taste sensations.

56 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question Why is it that the longer you are in a newly painted room, the less you are able to smell the paint?

57 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer Olfactory receptors are very sensitive, but they adapt easily, which explains why odors that are at first very noticeable are not sensed at all after a short period of time.

58 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Questions Where in the eye is light sensed? Where is it perceived (be specific).

59 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answers The innermost layer of the retina contains the rods and cones, which are the photoreceptor cells of the eye. Visual interpretation occurs in the visual cortex of the cerebrum.

60 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question We have discussed the importance of maintaining homeostasis in our bodies. We have seen how the integumentary system and muscular system contribute to homeostasis. How would you suggest that the general and special senses contribute to homeostasis?

61 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer The general and special senses help maintain homeostasis in the body by monitoring the conditions in our environment. For instance, heat and cold receptors help us to avoid conditions that will adversely affect temperature regulation in our body. Pain receptors tell us to avoid touching certain things. Because of special senses such as sight and hearing, we are able to avoid many dangerous situations, which helps maintain conditions within a normal range in the body. Our general and special senses are constantly accumulating data that are integrated with memory and reflexes to produce homeostatic responses

62 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question What is taking place with individuals who are unable to visually focus at a close distance?

63 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Answer As people age—onset is usually around age 40–45—they become farsighted and develop presbyopia due to the loss of elasticity of the crystalline lens. Usually reading glasses compensate for this condition.

64 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. ??? Questions ??? What questions do you have for me?