Chapter 13 | Sensory Systems

  1. Figure 13.5 Which of the following statements about mechanoreceptors is false?
    1. Pacini corpuscles are found in both glabrous and hairy skin.
    2. Merkel’s disks are abundant on the fingertips and lips.
    3. Ruffini endings are encapsulated mechanoreceptors.
    4. Meissner’s corpuscles extend into the lower dermis.
      Illustration shows the location of various mechanoreceptors in a cross section of the epidermis and dermis. A nerve runs along the middle of the dermis, and all the mechanoreceptors are connected to it. Ruffini endings, Merkel’s disks, and Meissners corpuscles are all located in the upper dermis above the nerve. Ruffini endings are bulbous, horizontal mechanoreceptors located in the middle of the upper dermis. Meissners corpuscles are bulbous, vertical mechanoreceptors that touch the bottom of the epidermis. Merkels disks have finger-like projections that also touch the bottom of the epidermis. The last type of mechanoreceptor, Pacini corpuscles, are oval mechanoreceptors located in the lower dermis.
      Figure 13.5 Four of the primary mechanoreceptors in human skin are shown. Merkel’s disks, which are unencapsulated, respond to light touch. Meissner’s corpuscles, Ruffini endings, Pacinian corpuscles, and Krause end bulbs are all encapsulated. Meissner’s corpuscles respond to touch and low-frequency vibration. Ruffini endings detect stretch, deformation within joints, and warmth. Pacinian corpuscles detect transient pressure and high-frequency vibration. Krause end bulbs detect cold.
  2. Figure 13.14 Cochlear implants can restore hearing in people who have a nonfunctional cochlear. The implant consists of a microphone that picks up sound. A speech processor selects sounds in the range of human speech, and a transmitter converts these sounds to electrical impulses, which are then sent to the auditory nerve. Which of the following types of hearing loss would not be restored by a cochlear implant?
    1. Hearing loss resulting from absence or loss of hair cells in the organ of Corti.
    2. Hearing loss resulting from an abnormal auditory nerve.
    3. Hearing loss resulting from fracture of the cochlea.
    4. Hearing loss resulting from damage to bones of the middle ear.
      A series of three illustrations are shown. The top illustration shows a cochlea, which is shaped like a snail shell with two parallel chambers, the upper chamber and the lower chamber, coiling from the outside in. These chambers are separated by a flexible membrane basilar membrane. The oval window covers the inner of these parallel chambers. Sound waves enter here, and travel to the middle, or apex, of the coil. The membrane separating the two chambers gets thinner from the outside in, such that is vibrates at different sound frequencies, about 20,000 hertz on the outside and about 200 hertz on the inside. Sound then travels back out through the lower chamber, and exits through the round window. The middle illustration shows a closer view of a cross-sectional image of the cochlea. A roughly circular shape has a roughly circular bone exterior, with the middle portion of the circle divided into four major areas. Two of these are spaces labeled “upper canal” and “lower canal.” In the middle is the organ of Corti, and extending from the middle out through the outer bone area is the cochlear nerve, which extends from the middle as a thin tube and then bulges into a larger oval shape as it extends through the bone. The bottom illustration is an enlarged image of the organ of Corti. In the view shown, the top section is a flattish pink area called the tectorial membrane. Extending beneath that membrane are three areas with hair-like connectors (stereocilia) that run from the membrane to the outer hair cells. The outer hair cells are shaped like rectangles with rounded corners. From the end of each protrudes a narrow tube: the cochlear nerve. These narrow tubes join to an inner hair cell, which looks similar to the outer hair cells but with its rectangular shape remaining a consistent width instead of narrowing into a nerve. At the bottom of the image, opposite the top tectorial membrane, is a basilar membrane.
      Figure 13.14 In the human ear, sound waves cause the stapes to press against the oval window. Vibrations travel up the fluid-filled interior of the cochlea. The basilar membrane that lines the cochlea gets continuously thinner toward the apex of the cochlea. Different thicknesses of membrane vibrate in response to different frequencies of sound. Sound waves then exit through the round window. In the cross section of the cochlea (top right figure), note that in addition to the upper canal and lower canal, the cochlea also has a middle canal. The organ of Corti (bottom image) is the site of sound transduction. Movement of stereocilia on hair cells results in an action potential that travels along the auditory nerve
  3. Figure 13.17 Which of the following statements about the human eye is false?
    1. Rods detect color, while cones detect only shades of gray.
    2. When light enters the retina, it passes the ganglion cells and bipolar cells before reaching photoreceptors at the rear of the eye.
    3. The iris adjusts the amount of light coming into the eye.
    4. The cornea is a protective layer on the front of the eye.
      The left illustration shows a human eye, which is round and filled with vitreous humour. The optic nerve and retinal blood vessels exit the back of the eye. At the front of the eye is the lens with a pupil in the middle. The lens is covered by the iris, which in turn is covered by the cornea, which is a convex bump protruding from the eye. The aqueous humour is a gel-like substance between the cornea and iris. The retina is the lining of the inner eye. A second illustration is a blowup which shows that the optic nerve is at the surface of the retina. Beneath the optic nerve is a layer of ganglion cells, and beneath this is a layer of bipolar cells. Both ganglia and bipolar cells are nerve cells with root-like appendages. Beneath the bipolar cell layer are the rods and cones. Rods and cones are similar in structure and column-like.
      Figure 13.17 (a) The human eye is shown in cross section. (b) A blowup shows the layers of the retina.

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