The senses

Editor's Notes

• #3: Sensory cells detect stimuli: chemical flavorings in your food; light emitted by your TV screen; tension in a muscle as you grasp a computer mouse; sound waves produced by your MP3 player; touch sensations as you hold someone’s hand; or other sensations such as electricity, cold, or heat.
• #5: Figure 29.2A on the facing page shows sensory transduction occurring when sensory receptor cells in a taste bud detect sugar molecules, as when you lick an ice cream cone.
• #6: In Figure 29.2B, the taste bud on the left has sensory receptors that respond to sugar, and the taste bud on the right responds to salt. The graphs in Figure 29.2B also indicate how action potentials communicate information about the intensity of stimuli. In each case, the left part of the graph represents the rate at which the sensory neurons in the taste bud transmit action potentials when the taste receptors are not stimulated. The right side of each graph shows that the rate of transmission depends on the intensity of the stimulus. The stronger the stimulus, the more neurotransmitter released by the receptor cell and the more frequently the sensory neuron transmits action potentials to the brain.
• #7: Specialized sensory receptors detect five categories of stimuli.
• #9: One of the most sensitive chemoreceptors in the animal kingdom is on the antennae of the male silkworm moth Bombyx mori (Figure 29.3C). The antennae are covered with thousands of sensory hairs (visible in the micrograph). The hairs have chemoreceptors that detect a sex pheromone released by the female.
• #12: The ear converts air pressure waves to action potentials that are perceived as sound. The human ear is really two separate organs, one for hearing and the other for maintaining balance.
• #13: (Figure 29.4B). Both the outer ear and middle ear are common sites of childhood infections (called swimmer’s ear and otitis media, respectively).
• #16: These pressure waves make your eardrum vibrate with the same frequency as the sound (Figure 29.4E). The frequency, measured in hertz (Hz), is the number of vibrations per second.
• #17: High-pitched sounds, such as high notes sung by a soprano, generate high-frequency waves. Low-pitched sounds, like the low notes made by a bass, generate low-frequency waves.
• #19: Several organs in the inner ear detect body position and movement.
• #20: Boating, flying, or even riding in a car can make us dizzy and nauseated, a condition called motion sickness. Because motion sickness can be a severe problem for astronauts, the National Aeronautics and Space Administration (NASA) conducts research on the problem. NASA has discovered that some people can learn to consciously control body functions, including the vomiting reflex. Astronauts receive intensive training in how to exert “mind over body” when zero gravity starts to induce motion sickness.
• #21: Most invertebrates have some kind of light-detecting organ. an important advantage for flying insects and other small animals often threatened by predators. also provide excellent color vision. Some species, such as honeybees, can see ultraviolet light (invisible to humans), which helps them locate certain nectar-bearing flowers. single-lens eye (squids)- (The single-lens eye found in squids and other invertebrates differs in some of the details.)
• #23: Humans have single-lens eyes that focus by changing position or shape
• #25: A gland above the eye secretes tears, a dilute salt solution that is spread across the eyeball by blinking and that drains into ducts that lead into the nasal cavities. This fluid cleanses and moistens the eye surface. Excess secretion in response to eye irritation or strong emotions causes tears to spill over the eyelid and fill the nasal cavities, producing sniffles. Some scientists speculate that emotional tears play a role in reducing stress.
• #27: If you can do this accurately, you have normal (20/20) acuity in each eye. This means that from a distance of 20 feet, each of your eyes can read the chart’s line of letters designated for 20 feet. Nearsighted– Nearsightedness A nearsighted eyeball is longer than normal (also known as myopia) is corrected by glasses or contact lenses that are thinner in the middle than at the outside edge. The lenses make the light rays from distant objects diverge as they enter the eye.
• #28: Farsighted people see distant objects normally but cannot focus on close objects.
• #29: The human retina contains two types of photoreceptors named for their shapes. The relative numbers of rods and cones an animal has correlates with whether an animal is most active during the day or night. Each human eye contains about 125 million rod cells and 6 million cone cells. (Rhodopsin is derived from vitamin A, which is why vitamin A deficiency can cause “night blindness.”)
• #30: RODS DO NOT DETECT COLOR.
• #31: Your senses of smell and taste depend on receptor cells that detect chemicals in the environment. Chemoreceptors in your taste buds detect molecules in solution; chemoreceptors in your nose detect airborne molecules.
• #32: Umami describes the savory flavor common in meats, cheeses, and other protein-rich foods, as well as the flavor-enhancing chemical monosodium glutamate (MSG).