2. action potential Abrupt, brief reversal in the resting membrane potential of excitable cells.
3. camera eye Of cephalopods and vertebrates, a camera-like eyeball with an inner darkened chamber, a single opening for light, and a retina (like film) on which visual stimuli are focused.
4. chemoreceptor Sensory receptor that detects ions or molecules dissolved in fluid bathing it.
5. cochlea The snail-shaped portion of the inner ear that houses the receptors for sound.
6. compound eye Crustacean or insect eye with multiple rodlike units, each of which samples part of the visual field.
7. cone cell In a vertebrate eye, a photoreceptor that responds to intense light and contributes to sharp daytime vision and color perception.
8. cornea Transparent cover over front of eye.
9. echolocation Use of echoes from self-generated ultrasounds as a navigational mechanism.
10. encapsulated receptor Skin mechanoreceptor; detects pressure, temperature, low vibrations.
11. external ear Among mammals, one of a pair of sound-collecting flaps on the sides of the head.
12. eye Sensory organ that incorporates a dense array of photoreceptors.
13. free nerve ending Simplest sensory receptor in skin, internal tissues; has unmyelinated or thinly myelinated branched endings.
14. hair cell Hairlike mechanoreceptor that is activated when sufficiently bent or tilted.
15. hearing Perception of sound.
16. inner ear Primary organ of equilibrium, and hearing, includes vestibular apparatus, cochlea.
17. lens A transparent body that bends light rays so that they converge onto photoreceptors.
18. mechanoreceptor Sensory cell or nearby cell that detects mechanical energy (changes in pressure, position, or acceleration).
19. middle ear Structures (ear drum, ear bones) that transmit air waves to the inner ear.
20. olfactory receptor Chemoreceptor for watersoluble or volatile substance.
21. osmoreceptor Sensory receptor; detects shifts in water volume (solute concentration).
22. otolith In organ of static equilibrium, a mass of calcium carbonate crystals embedded in a membrane that is sensitive to fluid movement.
23. pain Perception of injury to some body region.
24. pain receptor A nociceptor; a sensory receptor that detects tissue damage.
25. perception The conscious interpretation of some aspect of the external world created by the brain from nerve impulses generated by sensory receptors.
26. pheromone Hormone-like, nearly odorless exocrine gland secretion. A signaling molecule between individuals of the same species that integrates social behavior.
27. photoreceptor Light-sensitive sensory cell.
28. retina Dense array of photoreceptors in an eye.
29. rod cell Vertebrate photoreceptor sensitive to very dim light. Contributes to the coarse perception of movement across visual field.
30. sensation Conscious awareness of a stimulus.
31. sensory adaptation Decrease in response to a stimulus maintained at constant strength.
32. sensory system The ''front door'' of a nervous system; it detects external and internal stimuli and relays information to integrating centers that issue commands for responses.
33. somatic sensation Perception of touch, pain, pressure, temperature, motion, or positional changes of body parts.
34. somatosensory cortex Part of the outermost gray matter of the cerebral hemispheres.
35. special sense Vision, hearing, olfaction, or another sensation that arises from a particular location, such as the eyes, ears, or nose.
36. stimulus A specific form of energy (e.g., pressure, light, and heat) that activates a sensory receptor able to detect it.
37. taste receptor A chemoreceptor for substances dissolved in fluid bathing it.
38. thermoreceptor Sensory cell or specialized cell next to it that detects radiant energy (heat).
39. vestibular apparatus Organ of equilibrium.
40. vision Perception of visual stimuli. Light is focused on a dense layer of photoreceptors that sample details of a light stimulus, which are sent to the brain for image formation.
41. visual accommodation Adjustments in lens position or shape that focus light on a retina.
42. visual field The part of the outside world that an animal sees.