Sensory and Motor Mechanisms

Which one of the five categories of sensory receptors is primarily dedicated to external stimuli?

Why can eating “hot” peppers cause a person to sweat?

If you stimulate a sensory neuron electrically, how would that stimulation be perceived?

How are otoliths adaptive for burrowing mammals, such as the star-nosed mole?

Suppose a series of pressure waves in your cochlea caused a vibration of the basilar membrane that moves gradually from the apex toward the base. How would your brain interpret this stimulus?

If the stapes became fused to the other middle ear bones or to the oval window, how would this condition affect hearing? Explain.

Plants use statoliths to detect gravity (see Figure 39.22). How do plants and animals differ with regard to the type of compartment in which statoliths are found and the physiological mechanism for detecting their response to gravity?

Contrast the light-detecting organs of planarians and flies. How is each organ adaptive for the lifestyle of the animal?

In a condition called presbyopia, the eyes’ lenses lose much of their elasticity and maintain a flat shape. How would you expect this condition to affect a person’s vision?

Our brain receives more action potentials when our eyes are exposed to light even though our photoreceptors release more neurotransmitter in the dark. Propose an explanation.

Compare the function of retinal in the eye with that of the pigment chlorophyll in a plant photosystem (see Concept 10.2).

Explain why some taste receptor cells and all olfactory receptor cells use G protein-coupled receptors, yet only olfactory receptor cells produce action potentials.

Pathways involving G proteins provide an opportunity for an increase in signal strength in the course of signal transduction, a change referred to as amplification. How might this be beneficial in olfaction?

If you discovered a mutation in mice that disrupted the ability to taste sweet, bitter, and umami but not sour or salty, what might you predict about where this mutation acts in the signaling pathways used by these receptors?

Contrast the role of Ca²⁺ in the contraction of a skeletal muscle fiber and a smooth muscle cell.

Why are the muscles of an animal that has recently died likely to be stiff?

How does the activity of tropomyosin and troponin in muscle contraction compare with the activity of a competitive inhibitor in enzyme action?

The body masses of the animals used in these experiments ranged from about 0.001 g to 1,000,000 g, and their rates of energy use ranged from about 0.1 cal/(kg # m) to 100 cal/(kg # m). If you were to plot these data on a graph with linear instead of log scales for the axes, how would you draw the axes so that all data would be visible? What is the advantage of using log scales for plotting data with a wide range of values? (For additional information about graphs, see the Scientific Skills Review in Appendix F.)

Based on the graph, how much greater is the energy cost of flying for an animal that weighs 10^-3 g than for an animal that weighs 1 g? For any given form of locomotion, which travels more efficiently, a larger animal or smaller animal?

The slopes of the flying and swimming lines are very similar. Based on your answer to question 2, if the energy cost of a 2-g swimming animal is 1.2 cal/(kg .m), what is the estimated energy cost of a 2-kg swimming animal?

Considering animals with a body mass of about 100 g, rank the three forms of locomotion from highest energy cost to lowest energy cost. Were these the results you expected, based on your own experience? What could explain the energy cost of running compared to that of flying or swimming?

Schmidt-Nielson calculated the swimming cost in a mallard duck and found it was nearly 20 times as high as the swimming cost in a salmon of the same body mass. What could explain the greater swimming efficiency of salmon?

Contrast swimming and flying in terms of the main problems they pose and the adaptations that allow animals to overcome those problems.

Peristalsis contributes to the locomotion of many annelids and the movement of food in the digestive tract (see Concept 41.3). Using the muscles of your hand and a toothpaste tube as a model of peristalsis, how would your demonstration differ for the two processes?

When using your arms to lower yourself into a chair, you bend your arms without using your biceps. Explain how this is possible. (Hint: Think about gravity as an antagonistic force.)

Which of the following sensory receptors is incorrectly paired with its category?

(A) hair cell—mechanoreceptor

(B) snake pit organ—thermoreceptor

(C) taste receptor—chemoreceptor

(D) olfactory receptor—electromagnetic receptor

The middle ear converts 

(A) air pressure waves to fluid pressure waves. 

(B) air pressure waves to nerve impulses. 

(C) fluid pressure waves to nerve impulses. 

(D) pressure waves to hair cell movements.

During the contraction of a vertebrate skeletal muscle fiber, calcium ions

(A) break cross-bridges as a cofactor in hydrolysis of ATP.

(B) bind with troponin, changing its shape so that the myosin-binding sites on actin are exposed.

(C) transmit action potentials from the motor neuron to the muscle fiber.

(D) spread action potentials through the T tubules.

Which sensory distinction is not encoded by a difference in neuron identity? 

(A) white and red 

(B) red and green 

(C) loud and faint 

(D) salty and sweet

The transduction of sound waves into action potentials occurs

(A) in the tectorial membrane as it is stimulated by hair cells.

(B) when hair cells are bent against the tectorial membrane, causing them to depolarize and release neurotransmitter that stimulates sensory neurons.

(C) as the basilar membrane vibrates at different frequencies in response to the varying volume of sounds.

(D) within the middle ear as the vibrations are amplified by the malleus, incus, and stapes.

Although some sharks close their eyes just before they bite, their bites are on target. Researchers have noted that sharks often misdirect their bites at metal objects and that they can find batteries buried under sand. This evidence suggests that sharks keep track of their prey during the split second before they bite in the same way that

(A) a rattlesnake finds a mouse in its burrow.

(B) an insect avoids being stepped on.

(C) a star-nosed mole locates its prey in tunnels.

(D) a platypus locates its prey in a muddy river.

In general, locomotion on land will require more energy than locomotion in water. By integrating what you learned about animal form and function in Unit 7, discuss some of the evolutionary adaptations of mammals that support the high energy requirements for moving on land.

To help students appreciate how energy is stored in tendons during hopping, an instructor asked student volunteers to hop at a frequency that felt “natural” to them and then, after resting, to hop at exactly half that frequency. Hopping was done at a standard height and measurements were taken of mass, O₂ consumption, and CO₂ production. Here is a representative set of results calculated for one student.

The student consumed 159 joules/sec when standing. For each hop frequency, subtract this standing value from the energy used during hopping. Then divide by the hop frequency to calculate the energy cost per hop. How does the energy cost per hop differ at the two frequencies, and how might this be related to energy storage in tendons?

In a short essay (100–150 words), describe three ways in which the structure of the lens of the human eye is well adapted to its function in vision.

Bloodhounds, which are adept at following a scent trail even days old, have no more olfactory receptor genes than other dogs. Predict how the sensory and nervous systems of bloodhounds differ from those of other dogs in ways that contribute to their tracking ability.