Chapter 55

Summary		Questions		Media Resources
55.1 Animals employ a wide variety of sensory receptors.
• Mechanoreceptors, chemoreceptors, and photoreceptors are responsive to different categories of sensory stimuli; interoceptors and exteroceptors respond to stimuli that originate in the internal and external environments, respectively.		1.  Can you name a sensory receptor that does not produce a membrane depolarization?		•Introduction to Sense Organs
55.2 Mechanical and chemical receptors sense the body's condition.
• Muscle spindles respond to stretching of the skeletal muscle. • The sensory organs of taste are taste buds, scattered over the surface of a fish's body but located on the papillae of the tongue in terrestrial vertebrates. • Chemoreceptors in the aortic and carotid bodies sense the blood pH and oxygen levels, helping to regulate breathing. • Hair cells in the membranous labyrinth of the inner ear provide a sense of acceleration.		2.  What mechanoreceptors detect muscle stretch and the tension on a tendon? 3.  What structures in the vertebrate ear detect changes in the body's position with respect to gravity? What structures detect angular motion?		•Taste •Smell •Sense of Balance •Sense of Rotational Acceleration • Chemoreceptors •Sensory Receptors in Skin •Smell •Semicircular Canals and Ampulla
55.3 Auditory receptors detect pressure waves in the air.
• In terrestrial vertebrates, sound waves cause vibrations of ear membranes. • Different pitches of sounds vibrate different regions of the basilar membrane, and therefore stimulate different hair cells. • Bats and some other vertebrates use sonar to provide a sense of "lightless vision."		4.  How are sound waves transmitted and amplified through the middle ear? How is the pitch of the sound determined?		•Human Ear Anatomy •Hearing •Mechanoreceptors •Activity: Auditory Receptors • Hearing Loss and Jobs •Communication Frequencies •Going Batty
55.4 Optic receptors detect light over a broad range of wavelengths.
• A flexible lens focuses light onto the retina, which contains the photoreceptors. • Light causes the photodissociation of the visual pigment, thereby blocking the dark current and hyperpolarizing the photoreceptor; this inverse effect stops the inhibitory effect of the photoreceptor and thereby activates the bipolar cells.		5.  How does focusing in fishes and amphibians differ from that in other vertebrates? 6.  When a photoreceptor absorbs light, what happens to the Na+ channels in its outer segment?		•Human Eye Anatomy A Human Eye Anatomy B •Vision •Light Receptors •Eye Evolution • Retina Structure •Visual Processing Pathway
55.5 Some vertebrates use heat, electricity, or magnetism for orientation.
• The pit organs of snakes allow them to detect the position and movements of prey. Many aquatic vertebrates can detect electrical currents produced by muscular contraction. Some vertebrates can orient themselves using the earth's magnetic field.		7.  Why do rattlesnakes strike a moving lightbulb? 8.  How do sharks detect their prey? Why don't terrestrial vertebrates have this sense?

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