314 Ch 15 - The Chemical Senses

Odor map

See chemotopic map

Results of Mueller's Experiments Cyx Normal vs Cloned

Normal Mouse Has Cyx receptor Avoids Cyx Cloned Mouse No Cyx receptor Doesn't avoid Cyx

Results of Mueller's Experiments PTC Normal vs Cloned

Normal Mouse No PTC Doesn't avoid PTC Cloned Mouse Has PTC Avoids PTC

Pathways for olfaction

- Amygdala and Orbitofrontal Cortex - Amygdala and Piriform cortex - Amygdala and Olfactory Bulb - Olfactory mucosa to olfactory bulb - Olfactory bulb and piriform cortex - Piriform cortex and Orbitofrontal cortex

For example, Donald Wilson (2003) measured the response of neurons in the rat's piriform cortex to two odorants:

1. a mixture of isoamyl acetate, which has a banana-like odor, and peppermint and 2. the component isoamyl acetate alone.

Because the stimuli responsible for tasting and smelling are taken into the body, these senses are often seen as "gatekeepers" that

1. identify things that the body needs for survival and that should therefore be consumed and 2. detect things that would be bad for the body and that should therefore be rejected.

the location of the two main olfactory areas:

1. the piriform cortex, which is the primary olfactory area, and 2. the orbitofrontal cortex, which is the secondary olfactory area.

John O'Doherty and coworkers (2000) showed that both the pleasantness of a food-related odor and the brain's response to the odor can be influenced by satiety. Subjects were tested under two conditions:

1. when hungry, and 2. after eating bananas until satiety.

Olfactometer

A device that presents olfactory stimuli with great precision.

Calcium Imaging

A method of measuring receptor activity by using fluorescence to measure the concentration of calcium inside the receptor. This technique has been used to measure the activation of olfactory receptor neurons.

Bimodal neurons

A neuron that responds to stimuli associated with more than one sense.

Nasal pharynx

A passageway that connects the mouth cavity and the nasal cavity.

Tasters

A person who can taste the compound phenylthiocarbamide (PTC).

Nontasters

A person who cannot taste the compound phenylthiocarbamide (PTC).

Supertasters

A person who is especially sensitive to 6-n-propylthiouracil (PROP), a bitter substance.

2-Deoxyglucose Technique

A procedure that involves injecting a radioactive 2-deoxyglucose (2DG) molecule into an animal and exposing the animal to oriented stimuli. The 2DG is taken up by neurons that respond to the orientation. This procedure is used to visualize orientation columns in the cortex.

Olfactory receptors

A protein string that responds to odor stimuli.

Primary olfactory area

A small area under the temporal lobe that receives signals from glomeruli in the olfactory bulb. Also called the piriform cortex.

Taste buds

A structure located within papillae on the tongue that contains the taste cells.

Amygdala

A subcortical structure that is involved in emotional responding and in processing olfactory signals.

Optical Imaging

A technique that has been used to measure the activity of large areas of the olfactory bulb by measuring the intensity of red light reflected from the bulb.

Video microscopy

A technique that has been used to take pictures of papillae and taste buds on the tongue.

Figure 15.5

Across-fiber patterns of the response of fibers in the rat's chorda tympani nerve to three salts. Each letter on the horizontal axis indicates a different single fiber.

Insula

An area in the frontal lobe of the cortex that receives signals from the taste system and is also involved in the affective component of the perception of pain.

Frontal operculum cortex

An area in the frontal lobe of the cortex that receives signals from the taste system.

Secondary Olfactory Area

An area in the frontal lobe, near the eyes, that receives signals originating in the olfactory receptors. Also known as the orbitofrontal cortex.

Orbitofrontal cortex

An area in the frontal lobe, near the eyes, that receives signals originating in the olfactory receptors. Also known as the secondary olfactory cortex.

Piriform cortex

An area under the temporal lobe that receives signals from glomeruli in the olfactory bulb. Also called the primary olfactory cortex.

Figure 15.16

Areas in the rat olfactory bulb that are activated by various chemicals: a. a series of carbolic acids; b. a series of aliphatic alcohols.

Taste cells

Cell located in taste buds that causes the transduction of chemical to electrical energy when chemicals contact receptor sites or channels located at the tip of this cell.

Taste cells

Cells that make up a taste bud. There are a number of cells for each bud, and the tip of each one sticks out into a taste pore. One or more nerve fibers are associated with each cell.

Pheromones

Chemical signal released by an individual that affects the physiology and behavior of other individuals.

Taste buds

Contained on the papillae. There are about 10,000 taste buds.

Recognition threshold

For smell, the concentration at which the quality of an odor can be recognized.

Macrosmatic

Having a keen sense of smell; usually important to an animal's survival.

Microsmatic

Having a weak sense of smell. This usually occurs in animals like humans, in which the sense of smell is not crucial for survival.

Figure 15.12

Hundreds of molecules from the coffee, orange juice, and bacon are mixed together in the air, but the person just perceives "coffee," "orange juice," and "bacon." This perception of three odor objects from hundreds of intermixed molecules is a feat of perceptual organization.

Effect of What the Mother Consumes on Infant Preferences: Last Trimester - Water During Breast Feeding - Water

Intake of Carrot flavour - 0.51

Effect of What the Mother Consumes on Infant Preferences: Last Trimester - Water During Breast Feeding - Carrot Juice

Intake of Carrot flavour - 0.57

Effect of What the Mother Consumes on Infant Preferences: Last Trimester - Carrot Juice During Breast Feeding - Water

Intake of Carrot flavour - 0.62

Anosmia

Loss of the ability to smell due to injury or infection.

Table 15.3 Human Odor Detection Threshold

Methanol - 141, 000 Acetone - 15, 000 Formaldehyde - 870 Menthol - 40 T-butyl mercaptan 0.3

Figure 15.23

Odorant molecules released by food in the oral cavity and pharynx can travel through the nasal pharynx (dashed arrow) to the olfactory mucosa in the nasal cavity. This is the retronasal route to the olfactory receptors.

Figure 15.17

Patterns of activation in the rat olfactory bulb for seven different odorants. Yellow and red areas indicate areas of high activation compared to activation caused by exposure to air. Each odorant causes a distinctive pattern of activation.

Figure 15.15

Recognition profiles for some odorants. Large dots indicate that the odorant causes a high firing rate for the receptor listed along the top; a small dot indicates a lower firing rate for the receptor. The structures of the compounds are shown on the right.

Figure 15.20

Response determined by optical imaging to octanol (red) and hexanol (green) in the rat piriform cortex. In a few instances, both chemicals activate the same neurons (yellow).

Figure 15.7

Responses of three neurons recorded from the cell bodies of chorda tympani nerve fibers in the rat. Solutions of sucrose, salt (NaCl), hydrochloric acid (HCl), and quinine hydrochloride (QHCl) were flowed over the rat's tongue for 15 seconds, as indicated by the horizontal lines below the firing records. Vertical lines are individual nerve impulses. a. Neuron responds selectively to sweet stimulus; b. neuron responds selectively to salt; c. neuron responds to salty, sour, and bitter stimuli.

Odotopic map

See chemotopic map

Olfactory receptor neurons (ORNs)

Sensory neurons located in the olfactory mucosa that contain the olfactory receptors.

Receptor sites

Sites located on the tips of the taste cells. There are different types of sites for different chemicals. Chemicals contacting the sites cause transduction by affecting ion flow across the membrane of the taste cell.

Glomeruli

Small structures in the olfactory bulb that receive signals from similar olfactory receptor neurons. One function of each glomerulus is to collect information about a small group of odorants.

Figure 15.2 a. The tongue, showing the four different types of papillae. b. A fungiform papilla on the tongue; each papilla contains a number of taste buds. c. Cross section of a taste bud showing the taste pore where the taste stimulus enters. d. The taste cell; the tip of the taste cell is positioned just under the pore. e. Close-up of the membrane at the tip of the taste cell, showing the receptor sites for bitter, sweet, sour, and salty substances.

Stimulation of these receptor sites, as described in the text, triggers a number of different reactions within the cell (not shown) that lead to movement of charged molecules across the membrane, which creates an electrical signal in the receptor.

Figure 15.6 Mouse behavioral response to PTC.

The blue curve indicates that a normal mouse will drink PTC even in high concentrations. The red curve indicates that a mouse that has a human bitter-PTC receptor avoids PTC, especially at high concentrations.

Figure 15.8

The blue lines show how two neurons in the rat NST respond to a number of different taste stimuli (along the horizontal axis). The neuron in a. responds strongly to compounds associated with salty tastes. The neuron in b. responds to a wide range of compounds. The purple lines show how these two neurons fire after the sodium-blocker amiloride is applied to the tongue. This compound inhibits the responses to salt of neuron (a) but has little effect on neuron (b).

Figure 15.4

The central pathway for taste signals, showing the nucleus of the solitary tract, where nerve fibers from the tongue and the mouth synapse in the medulla at the base of the brain. From the nucleus of the solitary tract, these fibers synapse in the thalamus and then the insula and frontal operculum, which are the cortical areas for taste.`

Oral capture

The condition in which sensations from both olfaction and taste are perceived as being located in the mouth.

Figure 15.1

The contribution of each of the four basic tastes to the tastes of KCl and NaNO3, determined by the method of magnitude estimation. The height of the line indicates the size of the magnitude estimate for each basic taste.

Neurogenesis

The cycle of birth, development, and death of a neuron. This process occurs for the receptors for olfaction and taste.

Sensory-specific satiety

The effect on perception of the odor associated with food eaten to satiety (the state of being satiated or "full"). For example, after eating bananas until satiety, the pleasantness rating for vanilla decreased slightly (but was still positive), but the rating for banana odor decreased much more and became negative.

Proust Effect

The elicitation of memories through taste and olfaction. Named for Marcel Proust, who described how the taste and smell of a tea-soaked madeleine cake unlocked childhood memories.

Figure 15.28

The facial expressions of 3- to 8-hour-old infants in response to some food-related odors. Each horizontal row shows the reactions of the same infant to the following stimulation: C = control, odorless cotton swab; BA/VA = artificial solution of banana or vanilla; FI = artificial fish or shrimp odor; RE = Artificial rotten egg odor. The infants were tested prior to the first breast- or bottle-feeding.

Detection threshold

The minimum amount of energy that can be detected. The detection threshold for smell is the lowest concentration at which an odorant can be detected. This threshold is distinguished from the recognition threshold, which requires a higher concentration of odorant.

Nucleus of the Solitary Tract

The nucleus in the brain stem that receives signals from the tongue, the mouth, and the larynx transmitted by the chorda tympani, glossopharyngeal, and vagus nerves.

Retronasal route

The opening from the oral cavity, through the nasal pharnyx, into the nasal cavity. This route is the basis for the way smell combines with taste to create flavor.

Chemotopic map

The pattern of activation in the olfactory system in which chemicals with different properties create a "map" of activation based on these properties. For example, there is evidence that chemicals are mapped in the olfactory bulb based on carbon-chain length. Also called odor map.

Across-fiber patterns

The pattern of nerve firing that a stimulus causes across a number of neurons. Also referred to as distributed coding.

Recognition profile

The pattern of olfactory activation for an odorant, indicating which ORNs (olfactory receptor neurons) are activated by the odorant.

Flavor

The perception that occurs from the combination of taste and olfaction.

Tongue

The receptor sheet for taste. Contains papillae and all of the other structures described below.

Olfactory mucosa

The region inside the nose that contains the receptors for the sense of smell.

Olfaction

The sense of smell. Usually results from stimulation of receptors in the olfactory mucosa.

Odour objects

The source of an odor, such as coffee, bacon, a rose, or car exhaust.

Figure 15.13

The structure of the olfactory system. Odorant molecules flow over the olfactory mucosa, which contains 350 different types of olfactory receptor neurons (ORNs). Three types of neurons are shown here, indicated by different colors. Each type has its own specialized receptors.

Olfactory bulb

The structure that receives signals directly from the olfactory receptors. The olfactory bulb contains glomeruli, which receive these signals from the receptors.

Papillae

The structures that give the tongue its rough appearance. There are four kinds, each with a different shape.

Figure 15.3

The surface of the tongue. The red dots are fungiform papillae.

Figure 15.10

This diagram shows the different components of an olfactometer. By adjusting the valves in this system, the experimenter can vary both the humidity and the concentration of olfactory stimuli reaching the subject's nose.

Structures in the Taste System

Tongue Papillae Taste buds Taste cells Receptor sites

Figure 15.14

a. A portion of the olfactory mucosa. The mucosa contains 350 types of ORNs and about 10,000 of each type. The red circles represent 10,000 of one type of ORN, and the blue circles, 10,000 of another type. b. All ORNs of a particular type send their signals to one or two glomeruli in the olfactory bulb.

Figure 15.21 A model of how memories are formed in the cortex

a. Initially, incoming information activates a number of areas in the cortex. Tan rectangles are different cortical areas. Red circles are activated areas. b. As time passes, the neural activity is replayed, which creates connections between activated areas. c. Eventually, the activated areas for a particular memory are linked, which stabilizes the memory.

Figure 15.27 Sensory-speific satiety. Results of the O'Doherty et al. (2000) experiment.

a. Pleasantness rating for banana and vanilla odor before eating (left bars) and after eating bananas to satiety (right bars). b. Response of the orbitofrontal cortex to banana and vanilla odors before and after eating bananas.

Figure 15.26 Effect of expectation on flavor perception, as indicated by the results of Hilke Plassman's (2009) experiment.

a. The red and blue bars indicate ratings given to two presentations of the same wine (although subjects didn't know they were the same). The two bars on the left indicate ratings when there were no price labels on the wines. The two bars on the right indicate that the subject's give higher "taste pleasantness" ratings when the wine is labeled $90, compared to when it is labeled $10. b. Responses of the OFC when tasting the wines labeled $10 and $90.

Figure 15.11

a. Two molecules that have the same structure, but one smells like musk and the other is odorless. b. Two molecules with different structures but similar odors.

Figure 15.9

a. Video micrograph of the tongue showing the fungiform papillae of a "supertaster"—a person who is very sensitive to the taste of PROP. b. Papillae of a "nontaster"—someone who cannot taste PROP. The supertaster has both more papillae and more taste buds than the nontaster.

The process of tasting begins with the tongue (Figure 15.2a and Table 15.1). The surface of the tongue contains many ridges and valleys caused by the presence of structures called papillae, which fall into four categories:

1. filiform papillae, which are shaped like cones and are found over the entire surface of the tongue, giving it its rough appearance; 2. fungiform papillae, which are shaped like mushrooms and are found at the tip and sides of the tongue (see Figure 15.3); 3. foliate papillae, which are a series of folds along the back of the tongue on the sides; and 4. circumvilliate papillae, which are shaped like flat mounds surrounded by a trench and are found at the back of the tongue.

Electrical signals generated in the taste cells are transmitted from the tongue in a number of different nerves:

1. the chorda tympani nerve (from taste cells on the front and sides of the tongue); 2. the glossopharyngeal nerve (from the back of the tongue); 3. the vagus nerve (from the mouth and throat); and 4. the superficial petronasal nerve (from the soft palette—the top of the mouth).

Taste pore

An opening in the taste bud through which the tips of taste cells protrude. When chemicals enter a taste pore, they stimulate the taste cells and result in transduction.