Psychology2016

Sensation and Perception 115

OLFACTORY RECEPTOR CELLS The olfactory receptor cells each have about a half dozen

to a dozen little “hairs,” called cilia, that project into the cavity. Like taste buds, there

are receptor sites on these hair cells that send signals to the brain when stimulated by

the molecules of substances that are in the air moving past them.

Wait a minute—you mean that when I can smell something like a

skunk, there are little particles of skunk odor IN my nose?

Yes. When a person is sniffing something, the sniffing serves to move molecules

of whatever the person is trying to smell into the nose and into the nasal cavities. That’s

okay when it’s the smell of baking bread, apple pie, flowers, and the like, but when it’s

skunk, rotten eggs, dead animals—well, try not to think about it too much.

Olfactory receptors are like taste buds in another way, too. Olfactory receptors also have

to be replaced as they naturally die off, about every 5–8 weeks. Unlike the taste buds, there

are many more than 5 types of olfactory receptors—in fact, there are at least 1,000 of them.

Signals from the olfactory receptors in the nasal cavity do not follow the same path as

the signals from all the other senses. Vision, hearing, taste, and touch all pass through the

thalamus and then on to the area of the cortex that processes that particular sensory infor-

mation. But the sense of smell has its own special place in the brain—the olfactory bulbs.

THE OLFACTORY BULBS The olfactory bulbs are located right on top of the sinus cav-

ity on each side of the brain directly beneath the frontal lobes. (Refer to Figure 3.15.)

The olfactory receptors send their neural signals directly up to these bulbs, bypassing

the thalamus, the relay center for all other sensory information. The olfactory infor-

mation is then sent from the olfactory bulbs to higher cortical areas, including the pri-

mary olfactory cortex (the piriform cortex), the orbitofrontal cortex, and the amygdala

(remember from Chapter Two that the orbitofrontal cortex and amygdala play import-

ant roles in emotion). to Learning Objectives 2.11 and 2.12.

olfactory bulbs

two DulD-liMe RroLections of the Drain

located Lust aDove the sinus cavity

and Lust Delow the frontal loDes that

receive information from the olfactory

receRtor cells.

Chemical Senses

taste/gustation

smell/olfaction

called a chemical sense because substance molecules are suspended in the air,

carried to the nasal cavity, and fit into receptor sites

unique in that signals do not first travel to the thalamus before going to the brain

nose serves as a collection device

made possible largely through the role of taste buds (taste receptor cells)

called a chemical sense because food molecules dissolve

in saliva, which then fits into receptor sites

five basic tastes (receptor types)

sweet

sour

salty

bitter

umami

Concept Map L.O. 3.10, 3.11

Interactive

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Practice Quiz How much do you remember?

Pick the best answer.

1. Taste is often called a ____ sense because it works with
   the molecules of foods that people eat.
   a. physical c. chemical
   b. psychological d. electrical


2. Research has found that taste information is sent to the
   a. pons and medulla. c. cerebellum and parietal lobe.
   b. suprachiasmatic nucleus. d. insula and frontal operculum.
   3. How often are olfactory receptors replaced by new olfactory receptors?
   a. every 12–24 hours c. every 30 days
   b. every 2–3 days d. every 5–8 weeks
   4. Olfactory receptors project directly to the ____ and are
   unique in that signals do not first connect to the thalamus.
   a. occipital lobe c. hypothalamus
   b. olfactory bulbs d. gustatory cortex