Principles Of Animal Physiology 2nd Edition Christopher D. Moyes Test Bank

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Principles Of Animal Physiology 2nd Edition Christopher D. Moyes Test Bank

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Chapter 6 Sensory Systems
Principles of Animal Physiology, 2e (Moyes/Schulte)

1)

A paramecium is capable of responding to
A)

touch.
B)

chemicals.
C)

temperature.
D)

all of the above
Answer:

D
Page Ref: 248

2)

What defines a cell as an afferent neuron?
A)

It has the capacity to respond to environmental stimuli.
B)

It is located at the periphery.
C)

It has an axon that carries information to integrating centers.
D)

It has receptor proteins in its membrane.
Answer:

C
Page Ref: 251

3)

When a sensory receptor is an afferent neuron, the membrane potential that is initiated by a stimulus is called a
A)

generator potential.
B)

receptor potential.
C)

synaptic potential.
D)

action potential.
Answer:

A
Page Ref: 251

4)

Which of the following is NOT one of the steps of sensory processing?
A)

transduction of the signal
B)

transmission of the signal to the integrating center
C)

perception of the stimulus at the integrating center
D)

motor response to the signal
Answer:

D
Page Ref: 250

5)

A sensory illusion called paradoxical cold happens when a point heat stimulus is applied to a cold patch of skin, and is perceived as cold, not hot. This illusion happens due to
A)

labeled-line pathways.
B)

population coding.
C)

both heat and cold receptors on the same sensory neuron.
D)

lateral inhibition.
Answer:

A
Page Ref: 253 and 297

6)

Select the pair below that does not match.
A)

chemoreceptors detect chemicals
B)

photoreceptors detect light
C)

mechanoreceptors detect magnetic fields
D)

thermoreceptors detect temperature
Answer:

C
Page Ref: 252

7)

For sensory receptor cells, the threshold of detection is the weakest stimulus that produces
A)

a response.
B)

a response 50 percent of the time.
C)

a response 100 percent of the time.
D)

a maximum response magnitude.
Answer:

B
Page Ref: 255

8)

When a stimulus is continually applied but the action potential frequency declines, this is called
A)

receptor attenuation.
B)

receptor acclimation.
C)

receptor accommodation.
D)

receptor adaptation.
Answer:

D
Page Ref: 257

9)

In aquatic vertebrates, gustation always involves detecting sensations involved with
A)

predators.
B)

potential mates.
C)

food.
D)

all of the above
Answer:

C
Page Ref: 258

10)

Advantages of populations of receptors, as opposed to individual receptors, include
A)

improved sensory discrimination.
B)

improved stimulus intensity.
C)

improved signal firing rate.
D)

all of the above
Answer:

A
Page Ref: 253, 254

11)

Odorant receptors are
A)

carbohydrates.
B)

proteins.
C)

nucleic acids.
D)

lipids.
Answer:

B
Page Ref: 259

12)

Each olfactory neuron expresses __________ odorant receptor protein and each odorant receptor protein can recognize __________ odorant.
A)

one; one
B)

more than one; one
C)

one; more than one
D)

more than one; more than one
Answer:

C
Page Ref: 259, 260

13)

In olfactory receptor cells, signal transduction cascades often follow this order:
A)

receptor binding G-protein activation cAMP cell depolarization
B)

cell depolarization increased intracellular Ca2+ adenylate cyclase activation
C)

receptor binding opening ion channels G protein activation cell depolatization
D)

cell depolarization adenylate cyclase G-protein activation conformational change
Answer:

A
Page Ref: Fig. 6.7

14)

The epithelium of the vomeronasal organ is similar to the olfactory epithelium in which way?
A)

Both express the same chemoreceptors.
B)

physical location
C)

Both activate the same signal transduction pathway.
D)

none of the above
Answer:

D
Page Ref: 260

15)

Bitter and sour tastes are generally associated with
A)

carbohydrates.
B)

proteins.
C)

ions.
D)

toxic substances.
Answer:

D
Page Ref: 262

16)

Among vertebrates, taste buds share certain common features. Which of the following is FALSE?
A)

They are onion shaped.
B)

They have a pore that opens out to the surface of the body.
C)

They have numerous microvilli on the apical surface.
D)

They are single neurons.
Answer:

D
Page Ref: Fig 6.10

17)

Which of the following statements about taste is FALSE?
A)

K+ conveys salty.
B)

H+ conveys sour.
C)

Sugars convey sweet.
D)

Amino acids convey umami.
Answer:

A
Page Ref: 262

18)

In the salamander, the sour taste receptor cells function by having an apically localized K+ channel that is blocked by protons. When protons are applied, what happens to the membrane potential and why?
A)

Receptor depolarization because K+ permeability, which normally maintains a hyperpolarized resting state, is reduced.
B)

Receptor hyperpolarization because H+ ions move into the cell and render it more positively charged.
C)

Receptor hyperpolarization because the H+ ions outside the cell make the inside of the cell more negatively charged.
D)

Nothing will happen until the G protein is activated.
Answer:

A
Page Ref: 262

19)

Which of the following lists is in the correct order? Sweet tastes are processed in the following way:
A)

receptor binding, gustducin activated, adenylate cyclase activated, K+ channels close.
B)

receptor binding, Na+ channels open, cell depolarizes.
C)

gustducin activated, Ca2+ channels close, cell hyperpolarizes.
D)

transducin activated, PLC activated, Ca2+ levels rise, neurotransmitter released.
Answer:

A
Page Ref: Fig. 6.11c, 264

20)

Which taste receptor does NOT use a G-protein-coupled receptor for activation?
A)

bitter
B)

sweet
C)

salty
D)

umami
Answer:

C
Page Ref: Fig. 6.11, 264

21)

Mechanoreceptors translate mechanical signals into electrical signals when pressure on the cell
A)

activates a G protein signal transduction cascade.
B)

disrupts stability of the lipid bilayer, causing ions to flow.
C)

induces a conformational change in ion channels, allowing ions to flow.
D)

induces a change in cell volume that disrupts ion balance.
Answer:

C
Page Ref: 266

22)

Merkels disks are used by the visually impaired for reading Braille. One quality of the receptor that allows this is
A)

a phasic firing.
B)

small receptive field.
C)

a special sensitivity to deep pressure on the skin.
D)

a large dendritic tree.
Answer:

B
Page Ref: 266

23)

A thin piece of dome-shaped cuticle was found near one of the joints in a cricket leg. When it was removed, the animal could no longer make coordinated movements, but it could still respond to the rapid approach of a predator. This structure is most likely a
A)

trichoid sensilla.
B)

campaniform sensilla.
C)

joint capsule receptor.
D)

muscle spindle.
Answer:

B
Page Ref: 267

24)

Without a proprioceptive sense, you would NOT be able to
A)

clap your hands behind your back.
B)

feel grains of sand on your fingertips.
C)

autonomically control blood pressure.
D)

sense changes in temperature.
Answer:

A
Page Ref: 266

25)

You are riding your bicycle over a very bumpy road, reading a street sign far ahead of you. Which sensory inputs are NOT required to accomplish this task?
A)

proprioceptors
B)

visual inputs
C)

inner ear
D)

All of the above are required.
Answer:

D
Page Ref: 266

26)

Ruffini corpuscles are associated with __________ and detect __________.
A)

the skin surface; light touch and pressure
B)

hair follicles; changes in movement on the skin surface
C)

connective tissue of skin; skin stretch
D)

deep subcutaneous tissue, muscle, joints; deep pressure and touch
Answer:

C
Page Ref: 267

27)

Mechanoreceptors are important for
A)

touch.
B)

proprioception.
C)

hearing.
D)

all of the above
Answer:

D
Page Ref: 265

28)

In regards to hair cells involved in vertebrate hearing organs, we know that
A)

stereocilia are connected to each other by small fibers.
B)

mechanosensitive ion channels at the tips of stereocilia are all closed at rest.
C)

the 9 + 2 arrangement of stereocilia allow for free bending to improve sound resolution.
D)

their bending always causes an increase in firing in the primary afferent.
Answer:

A
Page Ref: 270, 271

29)

Which of the following structures from the vertebrate inner ear is NOT part of the vestibular apparatus?
A)

ampulla
B)

utricule
C)

saccule
D)

cochlea
Answer:

D
Page Ref: 273

30)

The hair cells of the mammalian cochlea are contained in the
A)

vestibular duct.
B)

tympanic membrane.
C)

round window.
D)

organ of Corti.
Answer:

D
Page Ref: 278

31)

The small bones in the mammalian middle ear are called:
A)

malleus, incus, stapes.
B)

stapes, ossicle, tectorus.
C)

malleus, otolith, statocyst.
D)

utricle, saccule, ampulla.
Answer:

A
Page Ref: Fig. 6.26

32)

If the orientation of your ears were changed so that your right ear still faced forward but your left ear faced backward, how would your ability to locate the direction of an auditory stimulus change?
A)

improved ability to distinguish left from right
B)

improved ability to distinguish above from below
C)

improved ability to distinguish front from back
D)

There would be no improved ability at all.
Answer:

C
Page Ref: 279

33)

Which of the following choices is FALSE? Mammalian rods and cones differ in that rods
A)

have fewer types of photopigment than cones.
B)

have a slower response time than cones.
C)

function better than cones in bright light.
D)

integrate signals over a longer period than cones.
Answer:

C
Page Ref: 283

34)

Which of the following choices is FALSE? The chromophore
A)

absorbs energy from photons.
B)

is a derivative of vitamin D.
C)

is covalently linked to a member of the opsin gene family.
D)

plays a role in photoreceptor sensitivity to different colors.
Answer:

B
Page Ref: 284

35)

Which of the following choices is FALSE regarding rhabdomeric photoreception?
A)

The absorption of light leads to cell hyperpolarization.
B)

The opsins signal through a Gq protein.
C)

A phospholipase C signal transduction cascade is activated.
D)

Diacylglycerol affects the activity of a nonselective cation channel.
Answer:

A
Page Ref: 284, 285

36)

Which eye structure constricts or dilates to control the amount of light that enters the eye?
A)

iris
B)

pupil
C)

retina
D)

lens
Answer:

A
Page Ref: 288

37)

The focal point is the
A)

point between the center of the lens and the retina.
B)

point where light waves converge after passing through the lens.
C)

small region in the center of the retina responsible for high-acuity vision.
D)

narrow band of the electromagnetic spectrum that contains visible light.
Answer:

B
Page Ref: 290

38)

Improving the resolving power of the compound eye would require
A)

increasing the number of ommatidia.
B)

increasing the size of each ommatidium.
C)

decreasing the size of the pinhole opening on each ommatidia.
D)

decreasing the thickness of the cornea.
Answer:

A
Page Ref: 287

39)

To generate an optimal visual image, the focal point must fall on the
A)

lens.
B)

fovea.
C)

retina.
D)

cornea.
Answer:

C
Page Ref: Fig. 6.36

40)

Why is vision sharpest in the fovea?
A)

It has more rods.
B)

It has more cones.
C)

There is less interference with overlying cells.
D)

It contains the focal point.
Answer:

C
Page Ref: 291

41)

What is the main difference between on and off region receptive fields?
A)

signal processing at the photoreceptor
B)

the type of neurotransmitter released by the photoreceptor
C)

the nature of the response of the bipolar cell to glutamate
D)

the presence of horizontal cells
Answer:

C
Page Ref: 293, 294

42)

In animals with binocular vision, it is true that
A)

neurons from the retina of the right eye project to the left lateral geniculate nucleus.
B)

neurons responding to the right visual fields project to the left lateral geniculate nucleus.
C)

neurons of the nasal retina project to the left lateral geniculate nucleus.
D)

neurons of the temporal retina project to the left lateral geniculate nucleus.
Answer:

B
Page Ref: Fig. 6.41

43)

In mammals, the circadian clock is located in the
A)

suprachiasmatic nucleus.
B)

retinal ganglion cells.
C)

visual cortex.
D)

pineal gland.
Answer:

A
Page Ref: 299

44)

All sensory systems work in the same general way. They transduce an incoming stimulus into changes in membrane
A)

potential.
B)

capacitance.
C)

refractory period.
D)

fluidity.
Answer:

A
Page Ref: 250

45)

In arthropods, the primary olfactory organs are generally located on the
A)

mandible.
B)

tympanum.
C)

ommatidia.
D)

antennae.
Answer:

D
Page Ref: 261

46)

Neurons are the only cells that can respond to environmental stimuli.
Answer:

FALSE
Page Ref: 248

47)

Sensory processing requires the release of neurotransmitter.
Answer:

TRUE
Page Ref: 250

48)

One similarity of all sensory receptors is that they must transduce some signal into a membrane potential.
Answer:

TRUE
Page Ref: 250

49)

Different sensory neurons use different types of action potentials to transmit information.
Answer:

FALSE
Page Ref: 251

50)

In vertebrates, each odorant receptor cell expresses only a single kind of odorant receptor protein. True
Answer:

FALSE
Page Ref: 260

51)

In vertebrates, each odorant receptor protein can bind only a single odorant.
Answer:

FALSE
Page Ref: 260

52)

Odor receptor proteins are always coupled to G proteins.
Answer:

TRUE
Page Ref: 259

53)

Proprioceptors normally fire phasically.
Answer:

FALSE

Page Ref: 267

54)

The activity of hair cells in the vertebrate inner ear depends on a high concentration of extracellular K+.
Answer:

TRUE
Page Ref: 271

55)

It is generally held that ciliary photoreceptors are associated with invertebrates, while rhabdomeric photoreceptors are associated with vertebrates.
Answer:

FALSE
Page Ref: 282

56)

The minimum criterion for calling something an eye, rather than a photoreceptor, is the ability to detect the direction by which light has entered the organ.
Answer:

TRUE
Page Ref: 285

57)

Despite the great diversity of eye structure, there is surprising similarity at the molecular level in the development of eyes in all animals.
Answer:

TRUE
Page Ref: Box 6.2

58)

To focus on an object, the cornea must modify its shape to some extent.
Answer:

FALSE
Page Ref: 290

59)

Unicellular eukaryotes cannot respond to environmental stimuli.
Answer:

FALSE
Page Ref: 250

60)

All sensory receptor cells are neurons.
Answer:

FALSE
Page Ref: 251

61)

The labeled line theory is based on the assumption that there is a discrete pathway from a sensory cell to the integrating center.
Answer:

TRUE
Page Ref: 253

62)

Many sensory receptor cells are epithelial cells.
Answer:

TRUE
Page Ref: 251

63)

A polymodal sensory receptor encodes different modalities using labeled line processing.
Answer:

FALSE
Page Ref: 253

64)

Because action potentials are all-or-none in nature, they normally code stimulus intensity through changes in firing frequency.
Answer:

TRUE
Page Ref: 255

65)

Bipolar neurons are often associated with sensory systems.
Answer:

TRUE
Page Ref: 251

66)

The vertebrate olfactory system can distinguish thousands of odorants through labeled line processing.
Answer:

FALSE
Page Ref: 251, 258

67)

Arthropods do not have external sensory structures because the hard exoskeleton prevents it.
Answer:

FALSE
Page Ref: Fig. 6.9, 6.14

68)

The gustatory system can discriminate as many compounds as the olfactory system.
Answer:

FALSE
Page Ref: 261

69)

Unlike taste receptor cells in vertebrates, invertebrate taste receptor cells are bipolar sensory neurons.
Answer:

TRUE
Page Ref: 264

70)

In Drosophila, each gustatory neuron appears to express only a single receptor protein.
Answer:

TRUE
Page Ref: 264

71)

Bitter-taste receptors do not depolarize when activated.
Answer:

TRUE
Page Ref: Fig. 6.11c

72)

Taste receptor proteins are always associated with G proteins.
Answer:

FALSE
Page Ref: Fig. 6.11

73)

The signal transduction pathways for olfaction and gustation are the same.
Answer:

FALSE
Page Ref: 259-264

74)

Mechanoreceptors make use of G proteins to transduce mechanical signals into electrical ones.
Answer:

FALSE
Page Ref: 266

75)

Vertebrate tactile receptors are grouped into complex mechanosensory organs.
Answer:

FALSE
Page Ref: 266

76)

Vertebrate hearing and equilibrium require the activity of hair cells, so-called because of the cilia that extend from the apical end of each cell.
Answer:

TRUE
Page Ref: 270

77)

In vertebrate hearing organs, the direction of bending of the hair-cell stereocilia will cause the sensory neuron to increase or decrease its firing frequency. In this way, stereocilia can code not only for movement, but for direction of movement.
Answer:

TRUE
Page Ref: 271

78)

Weakly electric fish have organs to generate electrical discharge, but do not have electroreceptors.
Answer:

FALSE
Page Ref: Box 6.1

79)

All vertebrates have an inner ear.
Answer:

TRUE
Page Ref: 273

80)

In terrestrial vertebrates, hearing involves the inner, middle, and outer ears.
Answer:

TRUE
Page Ref: 276

81)

The vestibular, tympanic, and cochlear ducts of the mammalian inner ear are filled with a substance called perilymph.
Answer:

FALSE
Page Ref: 279

82)

Eyespots are single cells.
Answer:

TRUE
Page Ref: 285

83)

A cup-shaped eye has improved discrimination in light direction and intensity over a flat sheet eye.
Answer:

TRUE
Page Ref: 286

84)

Stimulus intensity is normally coded by action potential __________.
Answer:

frequency
Page Ref: 255

85)

In response to a stimulus, a signal transduction pathway is initiated, which ultimately leads to the opening or closing of __________.
Answer:

ion channels
Page Ref: 250

86)

Sensory cells that respond to more than one class of stimulus are called __________ receptors.
Answer:

polymodal
Page Ref: 252

87)

To help discriminate the location of a touch stimulus, neurons at the center of the receptive field can inhibit those at the edge, a process known as __________.
Answer:

lateral inhibition
Page Ref: 254

88)

The top of a sensory cells dynamic range can be limited by the firing frequency of the primary afferent neuron. The maximum frequency is set by the __________ period.
Answer:

refractory
Page Ref: 256

89)

__________ are a kind of receptor that respond to extremely strong stimuli, including those that may cause tissue damage.
Answer:

Nociceptors
Page Ref: 252

90)

The __________ law describes the logarithmic relationship between stimulus magnitude and perceived stimulus intensity.
Answer:

Weber-Fechner
Page Ref: 256, 257

91)

In the vertebrate olfactory system, the olfactory receptor cells have one end in the olfactory epithelium, and the other end makes synapses with neurons in the __________ of the brain.
Answer:

olfactory bulb
Page Ref: 259

92)

Terrestrial vertebrates detect pheromones using an organ called the __________ organ.
Answer:

vomeronasal
Page Ref: 260

93)

In humans, tastes can be grouped into one of five classes, which are __________. (list all five)
Answer:

salty, sweet, bitter, sour, umami
Page Ref: 261

94)

In terrestrial vertebrates, taste receptor cells are clustered into groups known as __________.
Answer:

taste buds
Page Ref: 262

95)

In vertebrates, olfactory receptor cells are bipolar sensory neurons, but taste receptor cells are __________.
Answer:

epithelial cells
Page Ref: 264

96)

There are two main types of mechanoreceptor proteins: epithelial sodium channels and __________.
Answer:

transient receptor potential channels
Page Ref: 265

97)

Touch and pressure receptors can be broadly grouped into three categories: tactile receptors, proprioceptors, and __________.
Answer:

baroreceptors
Page Ref: 266

98)

A tympanal organ functions as an insect __________.
Answer:

ear
Page Ref: 270

99)

Fish, larval amphibians, and adult aquatic amphibians have cup-shaped organs called __________ that consist of mechanosensory hair cells to detect water movements such as those caused by potential predators.
Answer:

neuromasts
Page Ref: 271

100)

In carp, the inner ear is connected to the swim bladder by a series of bones called __________.
Answer:

Weberian ossicles
Page Ref: 275

101)

The compound called __________ can stimulate cold-sensitive neurons.
Answer:

menthol
Page Ref: 298

102)

The compound called __________ can stimulate warm-sensitive neurons.
Answer:

capsaicin
Page Ref: 298

103)

The organ of the inner ear of mammals that contains the hair cells is called the __________.
Answer:

organ of Corti
Page Ref: 279

104)

Invertebrates have organs called __________ that detect the orientation of their bodies with respect to gravity.
Answer:

statocysts
Page Ref: 268

105)

In the mammalian inner ear, inner hair cells detect sounds, while outer hair cells __________.
Answer:

amplify sounds
Page Ref: 278, 279

106)

Compound eyes are composed of many __________.
Answer:

ommatidia
Page Ref: 287

107)

Both the olfactory system and the gustatory system in vertebrates work by processing chemoreceptive signals. However, there are several differences between them. Describe/explain three differences.
Answer:

1. Olfactory receptor proteins are always coupled to G proteins, while gustatory receptor proteins have a variety of signal transduction mechanisms.
2. Olfactory neurons express only a single olfactory protein per cell, unlike gustatory receptor cells, which express more than one kind of receptor protein.
3. Olfactory receptor cells are bipolar sensory neurons, while gustatory receptor cells are epithelial cells that release neurotransmitter onto a primary afferent neuron.

Because a single taste neuron can synapse with more than one taste receptor cell, this suggests that coding of taste information is complex. It is unlikely that the coding of taste information works in a fashion by which a single taste is coded by a single neuron. This is different than processing in the olfactory system, where each neuron expresses only a single receptor protein, and therefore it is more likely that each neuron codes for a single olfactory sensation. The coding for tastants is probably very different than the coding for odorants.
Page Ref: 264

108)

Briefly describe lateral inhibition. Why is it useful? Draw a figure if necessary.
Answer:

Lateral inhibition is a process by which sensory activity at one location inhibits the activity of adjacent neurons. In other words, neurons that are stimulated will turn off neighboring neurons. The purpose of lateral inhibition is to enhance sensory contrast and improve edge detection. For example, imagine a pinprick on the surface of the skin. The source of the stimulus (i.e., the point of the pin) is very small, but its pressure on the skin will cause the skin around the pin tip to bend a little as well, which stimulates neighboring receptive fields. Without the process of lateral inhibition, the perception would be that a much larger object was touching the skin, and this would be inaccurate. Instead, lateral inhibition turns off neighboring cells (i.e., sensory cells around the pin), and more accurately codes for stimulus size by clearly coding for the stimulus edge.
Page Ref: 254 and 292, 293, Figures 6.3 and 6.39, 6.40

109)

How does the mammalian eye focus an image? In your description, name the important physical structures in image formation, define the focal point, and explain what accommodation is and why it is important.
Answer:

To create a clear image, light entering the eye must converge on a single point called the focal point, and this focal point must fall on the retina. However, light rays entering the eye are not always entering from the same direction. That is, light rays entering from a distant object are parallel when they strike the eye, but light rays entering from a nearby object are not parallel but are instead divergent. These light rays are bent once they hit the cornea and lens, and the light rays will converge. However, based on the difference in angles between distant and nearby objects, the light rays converge at different points beyond the lens. Light rays from distant objects have a short focal length (focal length: the distance from the center of a lens to its focal point). Light rays from nearby objects have a long focal length. In order to adjust the focal length and force the focal point onto the retina, a process called accommodation, the lens must change shape.

Additional information:
The cornea and the lens have a convex shape, which causes light rays to bend toward each other. While both of these structures contribute to image formation, the cornea is not capable of changing shape to fine-tune image formation.
The point where the light converges after passing through the lens is called the focal point.
Accommodation is the process by which the eye changes its focal length to ensure that the focal point falls on the retina. In mammals, this happens when the lens changes shape. This change is a function of the contraction or relaxation of the ciliary muscles of the eye, to cause the lens to become more rounded or flattened, respectively.
Page Ref: 290 and Figure 6

110)

Generally, how do sensory neurons encode stimulus intensity? What is the dynamic range of a sensory neuron? How does range fractionation improve the dynamic range?
Answer:

Sensory neurons change their firing rates to encode stimulus intensity. A higher intensity stimulus generally results in a higher frequency of firing, while a lower-intensity stimulus results in a lower frequency of firing. The dynamic range of a neuron is the range between the minimum and maximum signals that can be discriminated. At some point, the intensity of the stimulus will be so low in magnitude that the sensory neuron will not fire reliably. The threshold of detection is defined as the weakest stimulus that produces a response in a receptor 50% of the time, and it forms the lowest limit of the neurons dynamic range. At the top of the dynamic range, the neuron has reached its highest firing frequency, and cannot increase any more regardless of an increase in stimulus intensity. This saturation point forms the highest limit of the cells dynamic range. Range fractionation happens when different sensory cells are sensitive to different (but overlapping) portions of the dynamic range. Using a strategy in which groups of sensory neurons work together within a single sensory organ, this effectively allows the organ to code for a much wider range of stimulus intensities.
Page Ref: 255-6, Fig. 6.4

111)

It is late at night, and you are at the library doing some last-minute studying for your comparative physiology exam. You suddenly feel hungry, and you head to the vending machine to buy a snack. Explain the role of the following sensory structures/organs, and give an example of how/when they will be active during this task.

a. Merkel cell
b. Gustatory receptors (choose one)
c. Macula of a utricle
d. Cone photoreceptor
Answer:

Answers to this can be somewhat creative in giving examples for the use of these receptors.
a. Merkel cells are used for fine tactile discrimination, and may be used for handling coins, opening a bag of food, touching the food, etc. (see page 266).
b. Gustatory receptors: Depending on the type of snack, the student may describe the function of any of the receptors from page 263 (salty, sour, bitter, umami, sweet). For example, a bag of chips may be purchased, and the taste bud would be active with a particular focus on the reception of a salty signal. Sodium from salty food enters the receptor cell through a sodium channel, which causes cell depolarization. This depolarization results in calcium influx and consequent neurotransmitter release. The afferent neuron is activated.
c. The utricle is a part of the vestibular apparatus that is sensitive to linear acceleration. It would be active during forward walking motion. (see page 274, Fig. 6.22a)
d. Cone photoreceptors in vertebrates detect color. Therefore, these would be active when looking at all the different packages in the vending machine. (see page 283, Figure 6.29, and Table 6.1)
Page Ref: 266, 274, 283

112)

Why is it so difficult to localize sound with only one ear? How does having two ears help to localize sound?
Answer:

Sound is localized in two main ways. One way is through a TIMING DIFFERENCE. For example, if a sound is produced on the right side of the head, the sound will reach the right ear before it reaches the left. The brain can process this time lag, and the sound is perceived, correctly, as coming from the right. Sound is also localized through an INTENSITY DIFFERENCE. That is, when the same signal coming from the right passes through the head to reach the left ear, the sound intensity is altered. The brain can process this intensity difference, and the sound is perceived, correctly, as coming from the right. Two ears are required to process these differences, and that is why it is difficult to localize sound with only one ear.
Page Ref: 279

113)

In table format, list five differences in phototransduction between rhabdomeric and ciliary photoreceptors.
Answer:

Rhabdomeric Ciliary
11-cis 3-hydroxy retinal absorbs light and isomerizes into all-trans 3-hydroxy retinal
11-cis retinal absorbs light and isomerizes into all-trans retinal
All-trans 3-hydroxy retinal dissociates from opsin
All-trans retinal dissociates from opsin
Activated opsin activates a Gq protein Activated opsin activates the Gi protein transducin

Activated Gq activates PLC, converting PIP2 into DAG and IP3
Transducin activates PDE, which converts cGMP into GMP
DAG activates a TRP cation channel The decreased cGMP closes a Na+ channel

Ca2+ and Na+ enter the cell, depolarizing it Na+ entry decreases, hyperpolarizing the cell

Page Ref: Figure 6.32

114)

If all sensory signals are eventually transduced into the common action potential, then how do receptors encode stimulus modality? Give an example.
Answer:

One way in which sensory systems can code for stimulus modality is described by the theory of labeled lines. Since most sensory receptors are maximally sensitive to only one type of stimulus, and a sensory receptor is part of (or synapses with) a particular afferent neuron, signals in that afferent neuron must represent a specific stimulus modality. In other words, nociceptive afferent neurons are active ONLY in response to nociceptive stimuli, and thermal afferent neurons are active ONLY in response to thermal stimuli. In a common example, we know that the optic nerve transmits the signal light whenever the eye is stimulated, even if the stimulus is pressure on the eyeball.

The assumption with the labeled-line theory is that there is a discrete pathway from a sensory cell to the integrating center, but sensory connections are not always this simple. For example, polymodal receptors (e.g., ampullae of Lorenzini), which are sensitive to a variety of different stimuli, cannot code in the basic way laid out by the labeled-line theory. In this case, the afferent neuron may discriminate modality based on the firing pattern (e.g., high-frequency bursts instead of tonic firing). Additionally, neighboring polymodal receptors, with slightly different sensitivities to the various stimuli, may work together to send a coded signal to the afferent neuron. This type of cross-fiber coding is not well understood.
Page Ref: 252

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