Special Sensations

R1.1. Identify the structures in the following horizontal section of the eye. (PICTURE )

1. (a) vascular layer; (b) iris; (c) ciliary body; (d) choroid; (e) inner layer (retina); (f) neural part; (g) pigmented part; (h) fibrous layer; (i) cornea; (j) sclera

1. Define olfaction.

1. Olfaction is the sense of smell; it involves olfactory receptor cells in paired olfactory organs responding to chemical stimuli.

R10. Identify the structures of the external, middle, and internal ear in the following figure. (PICTURE)

10. (a) auricle; (b) external acoustic meatus; (c) tympanic membrane; (d) auditory ossicles; (e) semicircular canals; (f) vestibule; (g) auditory tube; (h) cochlea; (i) vestibulocochlear nerve (N VIII)

10. How would a blockage of the scleral venous sinus affect your vision?

10. If the scleral venous sinus (canal of Schlemm) were blocked, the aqueous humor could not drain, producing an eye condition called glaucoma. Accumulation of this fluid increases the pressure within the eye, distorting soft tissues and interfering with vision. If untreated, the condition would ultimately cause blindness.

11. If you had been born without cones in your eyes, would you still be able to see? Explain.

11. If you were born without cones, you would still be able to see—so long as you had functioning rods—but you would lack color vision and see in black and white only.

12. How could a diet deficient in vitamin A affect vision?

12. A vitamin A deficiency would reduce the quantity of retinal (retinene) the body could produce, thereby interfering with night vision (which operates at the body's threshold ability to respond to light).

13. What effect would a decrease in phosphodiesterase activity in photoreceptor cells have on vision?

13. Vision would be impaired. Decreased phosphodiesterase activity would increase intracellular cGMP levels, which, by keeping gated sodium channels open, would prevent both hyperpolarization of the photoreceptor cell and a decrease in its neurotransmitter release. There would be no signal to the bipolar cell that a photon had been absorbed.

R14. What are the four types of papillae on the human tongue?

14. (1) filiform papillae; (2) fungiform papillae; (3) foliate papillae; and (3) vallate papillae

14. If the round window were not able to bulge out with increased pressure in the perilymph, how would the perception of sound be affected?

14. If the round window could not move, the perilymph would not be moved by the vibration of the stapes at the oval window, reducing or eliminating the perception of sound.

R15. (a) What structures make up the fibrous layer of the eye? (b) What are the functions of the fibrous layer?

15. The fibrous layer (a) is composed of the sclera and the cornea and (b) provides mechanical support and some physical protection, serves as an attachment site for the extrinsic eye muscles, and contains structures that assist in the focusing process.

15. How would the loss of stereocilia from hair cells of the spiral organ affect hearing?

15. The loss of stereocilia (as a result of constant exposure to loud noises, for instance) would reduce hearing sensitivity and could lead to deafness.

16. Why would blockage of the auditory tube produce an earache?

16. If the auditory tube were blocked, it would not be possible to equalize the pressure on both sides of the tympanic membrane. If external pressure then decreases, the pressure in the middle ear would be greater than that on the outside, forcing the tympanic membrane outward and producing pain.

R16. What structures make up the vascular layer of the eye?

16. The vascular layer consists of the iris, ciliary body, and choroid.

R17. What are the three auditory ossicles in the middle ear, and what are their functions?

17. The malleus, incus, and stapes transmit a mechanical vibration (amplified along the way) from the tympanic membrane to the oval window.

R18. Trace the olfactory pathway from the time an odor reaches the olfactory epithelium until nerve impulses reach their final destination in the brain.

18. Axons leaving the olfactory epithelium collect into 20 or more bundles that penetrate the cribriform plate of the ethmoid bone to reach the olfactory bulbs of the cerebrum. Axons leaving the olfactory bulb travel along the olfactory tract to reach the olfactory cortex, hypothalamus, and portions of the limbic system.

R19. Why are olfactory sensations long-lasting and an important part of our memories and emotions?

19. Olfactory sensations are long lasting and important to memories because the sensory information reaches the cerebral cortex by the hypothalamus and the limbic system without first being filtered through the thalamus.

2. Trace the olfactory pathway, beginning at the olfactory epithelium.

2. Axons from the olfactory epithelium collect into bundles that reach the olfactory bulb. In the olfactory pathway, axons leaving the olfactory bulb then travel along the olfactory tract to the olfactory cortex, hypothalamus, and portions of the limbic system.

R20. What is the usual result if a sebaceous gland of an eyelash or a tarsal gland becomes infected?

20. An infected sebaceous gland of an eyelash or tarsal gland usually becomes a sty, a painful swelling.

R24. You are at a park watching some deer 35 feet away from you. A friend taps you on the shoulder to ask a question. As you turn to look at your friend, who is standing just 2 feet away, what changes would your eyes undergo?

24. Your medial rectus muscles would contract, directing your gaze more medially. In addition, your pupils would constrict and the lenses would become more spherical.

R25. Your friend Shelly suffers from myopia (nearsightedness). You remember from your physics class that concave lenses cause light waves to spread or diverge and that convex lenses cause light waves to converge. What type of corrective lenses would you suggest to your friend? (a) concave lenses, (b) convex lenses.

25. Myopia is corrected by (a) concave lenses.

R26. Tom has surgery to remove polyps (growths) from his sinuses. After he heals from the surgery, he notices that his sense of smell is not as keen as it was before the surgery. Can you suggest a reason for this?

26. In removing the polyps, some of the olfactory epithelium was probably damaged or destroyed, decreasing the area available for the solution of odorants and reducing the intensity of the stimulus. As a result, after the surgery it would take a larger stimulus to provide the same level of smell.

R27. For a few seconds after you ride the express elevator from the 20th floor to the ground floor, you still feel as if you are descending, even though you have come to a stop. Why?

27. The rapid descent in the elevator causes the otoliths of the saccular maculae to slide upward, producing the sensation of downward vertical motion. After the elevator abruptly stops, it takes a few seconds for the otoliths of the maculae to come to rest in the normal position. So long as the otoliths are displaced, you will perceive movement.

R28. Juan tells his physician that he has been feeling dizzy, especially when he closes his eyes. He is asked to stand with his feet together and arms extended forward. As long as he keeps his eyes open, he exhibits very little movement. But when he closes his eyes, his body begins to sway a great deal, and his arms tend to drift together toward the left side of his body. Why does this occur?

28. When Juan closes his eyes, visual cues are gone, and his brain must rely solely on proprioceptive information from the equilibrium centers of the internal ear to maintain normal posture. Because either the internal ear receptors or the sensory nerves are not functioning normally, he is unstable. The most likely reason for his drift to the left is that he is getting inappropriate sensations from equilibrium receptors, either at the maculae (affecting his ability to determine which way is "down") or one of the horizontal semicircular ducts (making him attempt to compensate for a perceived roll to the right).

3. When you first enter the A&P lab for dissection, you are very aware of the odor of preservatives. By the end of the lab period, the smell doesn't seem to be nearly as strong. Why?

3. By the end of the lab period, central adaptation has occurred. Inhibition of synapses along the olfactory pathway reduces the amount of information reaching the olfactory cortex, even though the olfactory neurons remain active.

4. Define gustation.

4. Gustation is the sense of taste, provided by taste receptors responding to chemical stimuli.

5. If you completely dry the surface of your tongue and then place salt or sugar crystals on it, you can't taste them. Why not?

5. Taste receptors (in taste buds) are sensitive only to molecules and ions that are in solution. If you dry the surface of your tongue, the salt ions or sugar molecules have no moisture in which to dissolve, so they will not stimulate the taste receptors.

6. Your grandfather can't understand why foods he used to enjoy just don't taste the same anymore. How would you explain this to him?

6. Your grandfather is experiencing the effects of several age-related changes. The number of taste buds decreases dramatically after age 50, and those that remain are not as sensitive as they once were. In addition, the loss of olfactory receptors contributes to the perception of fewer flavors in foods.

7. Which layer of the eye would be affected first by inadequate tear production?

7. The conjunctiva would be the first layer of the eye affected by inadequate tear production. Drying of the conjunctiva would produce an irritated, scratchy feeling.

8. When the lens of your eye is more rounded, are you looking at an object that is close to you or far from you?

8. When the lens becomes more rounded, you are looking at an object that is close to you.

9. As Sue enters a dimly lit room, most of the available light becomes focused on the fovea of her eye. Will she be able to see very clearly?

9. Sue will likely be unable to see at all. The fovea (fovea centralis) contains only cones, which need high-intensity light to be stimulated. The dimly lit room contains light that is too weak to stimulate the cones.

R21. Displacement of stereocilia toward the kinocilium of a hair cell (a) produces a depolarization of the membrane, (b) produces a hyperpolarization of the membrane, (c) decreases the membrane permeability to sodium ions, (d) increases the membrane permeability to potassium ions, (e) does not affect the membrane potential of the cell.

A

R23. When viewing an object close to you, your lens should be more ___________. (a) rounded, (b) flattened, (c) concave, (d) lateral, (e) medial.

A

R7. At sunset, your visual system adapts to (a) fovea vision, (b) rod-based vision, (c) macular vision, (d) cone-based vision.

B

R9. The malleus, incus, and stapes are the tiny bones located in the (a) external ear, (b) middle ear, (c) internal ear, (d) membranous labyrinth.

B

R13. Auditory information about the frequency and intensity of stimulation is relayed to the CNS over the cochlear branch of cranial nerve (a) IV, (b) VI, (c) VIII, (d) X.

C

R22. Damage to the cupula of the lateral semicircular duct would interfere with the perception of (a) the direction of gravitational pull, (b) linear acceleration, (c) horizontal rotation of the head, (d) vertical rotation of the head, (e) angular rotation of the head.

C

R3. A blind spot occurs in the retina where (a) the fovea is located, (b) ganglion cells synapse with bipolar cells, (c) the optic nerve attaches to the retina, (d) rod cells are clustered to form the macula, (e) amacrine cells are located.

C

R5. The basic receptors in the internal ear are the (a) utricles, (b) saccules, (c) hair cells, (d) supporting cells, (e) ampullae.

C

R6. The retina is also called (a) the vascular layer, (b) the fibrous layer, (c) the inner layer, (d) all of these.

C

R11. Receptors in the saccule and utricle provide sensations of (a) angular acceleration, (b) hearing, (c) vibration, (d) gravity and linear acceleration.

D

R12. The spiral organ is located in the ___________ of the internal ear. (a) utricle, (b) bony labyrinth, (c) vestibule, (d) cochlea.

D

R2. A reduction in sensitivity in the presence of a constant stimulus is (a) transduction, (b) sensory coding, (c) line labeling, (d) adaptation.

D

R8. A better-than-average visual acuity rating is (a) 20/20, (b) 20/30, (c) 15/20, (d) 20/15.

D

R4. Sound waves are converted into mechanical movements by the (a) auditory ossicles, (b) cochlea, (c) oval window, (d) round window, (e) tympanic membrane.

E