Chapter 8: Special Senses
Did You Get It?
1)What is the role of the eyelids? The eyelids protect the eyes. 2)Which four accessory glands or structures help lubricate the eye? The tarsal glands, ciliary glands, conjunctiva, and lacrimal glands all contribute to lubricating the eye, though their secretions differ. 3)What is the role of lysozyme in tears? Lysozyme is a component of tears that helps to destroy bacteria and protect the eye from infection. 4)What is the visual role of the external eye muscles? They direct the eyeball toward what you wish to view. 5)What is the meaning of the term blind spot in relation to the eye? The blind spot contains no photoreceptors; it is the site where the optic nerve leaves the eyeball. 6)What function does the choroid of the vascular layer have in common with the pigmented layer of the retina? Both contain pigment, which prevents light scattering in the eye. 7)How do the rods and cones differ from each other? Rods have a rodlike outer segment containing the photopigment, whereas cones have a shorter cone-shaped outer segment. Rods respond to low light conditions and produce black-and-white vision; cones need bright light and provide color vision. 8)What are the refractory media of the eye? Refractory media include the cornea, aqueous humor, the lens, and vitreous humor. 9)What name is given to the ability of the eye to focus on close objects? Accommodation. 10)What is the difference between the optic tract and the optic nerve? The optic nerves leave the eyeballs, and the medial half of the fibers of each optic nerve cross over to the opposite side, joining there with the fibers from the outside half of the opposite eye to form the optic tracts. 11)In what way does the photopupillary reflex protect the eyes? It causes pupillary constriction in very bright light. Intense light stimulation can injure the photoreceptors. 12)How is astigmatism different from myopia and hyperopia? Astigmatism results from unequal curvatures on the lens surface, not from an eyeball that is too long or too short to focus the image on the retina. The unequal curvatures of astigmatism result in points of light that focus on the retina as lines, not points, leading to blurry images. 13)Which region(s) of the ear (external, middle, or internal) serve hearing only? External and middle ears serve hearing only. 14)Which structures of the ear transmit sound vibrations from the eardrum to the oval window? The ossicles (hammer, anvil, and stirrup). 15)What sense do the vestibule and semicircular canals serve? Balance or equilibrium. 16)Describe the different receptors for static and dynamic equilibrium and their locations. Dynamic receptors located in the semicircular canals (crista ampullaris) have embedded in the gel-like cupula; static receptors located in the vestibule (maculae) have otoliths that move when the head moves, causing hairs embedded in the otolithic membrane to bend. 17)What are otoliths, and what is their role in equilibrium? Otoliths are tiny stones made of calcium salts that are located in the maculae of the vestibule. They respond to static equilibrium cues relative to the position of the head in space. 18)From the air outside the body, through what substances do sound waves travel to excite the receptor cells of the cochlea? Tympanic membrane to bones of ossicles to fluids of the cochlear scalae. 19)Which nerve transmits impulses from the spiral organ of Corti to the brain? Cochlear nerve (division of cranial nerve VIII). 20)Do high-pitched sounds peak close to or far from the oval window? Close to the oval window. 21)How do sensorineural deafness and conduction deafness differ from each other? Sensorineural deafness results from damage to neural structures involved in hearing (cochlear nerve, auditory region of the brain), whereas conductive deafness results from anything that prevents sound vibrations from reaching the cochlea (earwax, fusion of the ossicles, fluid in the middle ear). 22)What general name is used to describe both taste and smell receptors? Why? Chemoreceptors, because they respond to chemicals in solution. 23)Where, relative to specific structures, are most taste buds located? On the tongue. 24)Why does it help to sniff substances that you want to smell? Odor receptors are located at the superior aspect of the nasal cavity. Sniffing brings the air upward. 25)Fifty-year-old Mrs. Bates is complaining that she can't read without holding the newspaper out at arm's length. What is her condition, and what is its cause? Presbyopia; caused by reduced elasticity of the lens as a result of aging. 26)Which of the special senses is least mature at birth? Vision. 27)What is presbycusis? Deafness of old age.
Multiple Choice Questions
1.Gustatory cells are epithelial cells. 2.Alkaloids excite gustatory hairs mostly at the back of the tongue. vallate papillae. 3.Cranial nerves that are part of the gustatory pathway include facial. glossopharyngeal. 4.Which cranial nerve controls contraction of the circular smooth muscle of the iris? Oculomotor 5.The cornea is nourished by aqueous humor. 6.When the eye focuses for far vision, the lens is at its thinnest. the light rays are nearly parallel. 7.Convergence requires contraction of the medial rectus muscles of both eyes. is needed for near vision. involves transmission of impulses along the abducens nerves. can promote eyestrain. 8.Which of the following are paired incorrectly? Cochlear duct—cupula Ampulla—otoliths 9.Movement of the membrane triggers bending of hairs of the hair cells in the spiral organ of Corti. tectorial 10.Sounds entering the external acoustic meatus are eventually converted to nerve impulses via a chain of events including vibration of the eardrum. vibratory motion of the ossicles against the oval window. stimulation of hair cells in the spiral organ of Corti.
Additional Questions
Q: Which layer of the eye would be the first to be affected by deficient tear production? A: The outermost fibrous layer (the sclera and especially its cornea), which normally is continuously washed by tears. Q: How does sniffing help to identify scents? A: It brings more odor-containing air into contact with the olfactory receptors in the superior part of the nasal cavity.