Physiology of Taste and Smell
What percentage of all people exhibit taste blindness?
15-30%
How many sodium receptors are there for taste?
2
how many bitter receptors are there for taste?
2
how many potassium receptors are there for taste?
2
how many sweet receptors are there for taste?
2
What is a taste bud composed of?
50 modified epithelial cells; sustencular and taste
About how much does smell adapt in the first second?
50%
For practical analysis of taste, how many general categories are there and what are they?
5; sour, salty, sweet, bitter, umami
It is believed that the taste receptor for L-glutamate may be related to what?
one of the glutamate receptors expressed in neuronal synapses of the brain
How does the receptor potential change with sour taste sensations?
opening of specific hydrogen ion channels
How does the receptor potential change with salty taste sensations?
opening of specific sodium ion channels
What is the adaptation of smell probably due to?
probable presence of inhibitory cells in the olfactory bulb (granule cells)
What is the less old system of olfactory sensation?
provides automatic but partially learned control of food intake and aversion to toxic and unhealthy foods
What studies were performed to discover the different receptors for the primary sensations of taste?
psychophysiologic and neurophysiologic
What drugs used in medicine are considered alkaloids?
quinine, caffeine, strychnine, and nicotine
what do olfactory cilia do?
react to odors in air and stimulate the olfactory cells
olfactory cells
receptor cells for smell sensation
An increase in the intensity of bitter taste causes what?
the person or animal to reject the food
Describe what you know about taste cells.
they are continually being replaced by mitotic division of surrounding epithelial cells, some taste cells are young cells, others mature cells that lie toward the center of the bud, they have a life span in animals of about 10 days
Umami taste is dominant in what foods?
those containing L-glutamate, such as meat extracts and aging cheese
Taste buds are found on how many types of papillae of the tongue? What are these?
three 1. walls of the troughs that surround the circumvallate papillae, which form a V line on the surface of the posterior tongue 2. fungiform papillae over the flat anterior surface of the tongue 3. foliate papillae located in the folds along the lateral surfaces of the tongue
At high concentrations, taste buds can be excited by ___________ of the five primary taste stimuli
two or more
Sustencular cells
supporting cells of taste bud
What is the diameter of a taste bud?
1/30 mm
what is the threshold for bitter taste by quinine?
0.000008 M
T/F bitter taste is caused by a single class of chemicals
FALSE
What is the importance of the senses of taste and smell?
- allow us to separate undesirable or even lethal foods from pleasant desirable foods - allow animals to recognize the proximity of other animals or even individuals among animals -both senses are strongly tied to primitive emotional and behavioral functions of our nervous system
Describe the location of the olfactory membrane.
- lies in superior part of each nostril - medially folds downward along the surface of the superior septum - laterally folds over the superior turbinate and even over small portion of upper surface of middle turbinate
What is the length of a taste bud?
1/16 mm
What is the threshold for sour taste by hydrochloric acid?
0.0009 M
what is the threshold for salty taste by sodium chloride?
0.01 M
what is the threshold for sweet taste by sucrose?
0.01 M
How many chloride receptors are there for taste?
1
how many adenosine receptors are there for taste?
1
how many glutamate receptors are there for taste?
1
how many hydrogen ion receptors are there for taste?
1
how many inosine receptors are there for taste?
1
Give three examples of experiments that demonstrate the ability to choose certain foods.
1. adrenalectomized animals (salt-depleted) will automatically select drinking water rich in sodium chloride 2. animals given injections of excessive amounts of insulin will develop depleted blood sugar and therefore automatically choose the sweetest food 3. calcium depleted parathyroidectomized animals will automatically choose drinking water with high concentrations of calcium chloride
Give a brief summary of olfactory signal transduction.
1. odor substance diffuses in mucus 2. binds to receptor proteins on membrane clilum 3. G-protein on excitation releases subunit alpha 4. this activated adenyl cyclase 5. activated cyclase converts intracellular ATP to cAMP 6. cAMP activates gated Na+ channels 7. entrance of Na+ increase electrical potential exciting olfactory neuron 8. transmission of action potential to CS by way of olfactory nerve
T/F sweet taste is caused by a single class of chemicals.
FALSE, but most of the chemicals that cause a sweet taste are organic chemicals
T/F taste is more important than smell for the selection of food.
FALSE, smell is more important
T/F many vesicles form beneath the cell membrane near the taste nerve fibers
TRUE
T/F odors can be the primary excitant of sexual drive
TRUE
T/F olfactory cells are bipolar nerve cells that originate from the CNS itself
TRUE
T/F previous experience with unpleasant or pleasant tastes plays a major role in determining one's taste preferences.
TRUE
T/F some people are taste blind for certain substances.
TRUE
T/F some substances that at first taste sweet have a bitter aftertaste
TRUE
T/F Anions also contribute to salty taste.
TRUE, but to a lesser extent than cations
The outer tip of taste cells are arranged around what?
a taste pore
What is sour taste caused by?
acids, or hydrogen ion concentration
How does the receptor potential change with bitter taste sensation?
activate second messenger transmitter substances inside taste cells, causing intracellular chemical changes that elicit taste signals
How does the receptor potential change with sweet taste sensations?
activate second messenger transmitter substances inside taste cells, causing intracellular chemical changes that elicit taste signals
Extinction of the sense of smell within a minute is due to what?
additional adaptation that occurs in the CNS
What is the importance of taste?
allows a person to select food according to desires and body tissues' metabolic need for specific substances
What is the very old system of olfactory sensation?
basic olfactory reflexes
Why is the threshold for bitter taste so much more sensitive than any of the others?
because the bitter taste usually indicates things such as poisons or toxins to the body
How is the taste chemical itself gradually washed away from the taste villus?
by the saliva, which removes the stimulus
What are the seven primary sensations of smell?
camphoraceous, musky, floral, peppermint, ethereal, pungent, putrid
What is mainly responsible for the salty taste?
cations of salt, especially sodium cations
What happens to the potential of a taste cell due to application of a taste substance to taste hairs?
causes partial loss of this negative potential
What is the newer system of olfactory sensation?
conscious perception and analysis of olfaction
What are people especially taste blind for?
different types of thiourea compounds
Salty taste quality varies on what?
from salt to salt, some salts elicit other taste sensations in addition to saltiness
What is salty taste caused by?
ionized salts, mainly by sodium ion concentration
What is the charge of a taste cell?
it is negatively charged inside of the cell
Umami Taste
japanese for delicious, designates a pleasant taste sensation that is qualitatively different from sour, salty, sweet or bitter
What is bitter taste caused by?
long chain organic substances that contain nitrogen or alkaloids, which are deadly toxins found in poisonous plants
What is present on the tip of each taste cell?
microvilli (taste hairs)
At low concentrations, taste buds usually respond to ____________ of the five primary taste stimuli.
one
What other sense highly contributes to taste perception?
sense of smell
What is the least understood of all of the senses? why?
sense of smell, it is a subjective phenomenon, poorly developed in humans, and cant be studied using lower animals
taste preference
simply means that an animal will choose certain types of food in preference to others
The phenomenon of taste preference results from what?
some mechanism located in the CNS, not from mechanism in taste receptors
What is the tongue made up of?
stratified squamous epithelium
The more acidic the food, the _________________ the sour sensation becomes.
stronger
3rd order neurons
synapse at lower tip of postcentral gyrus in the parietal cerebral cortex into the adjacent opercular insular areas
1st order neurons
synapse at the nucleus of solitary tract
2nd order neurons
synapse at ventral posterior medial nucleus of thalamus; located slightly medial to the thalamic terminations of the facial regions of the dorsal column-medial lemniscal system
Taste is mainly a function of what?
taste buds in the mouth through the texture of food (tactual senses) and substances that stimulate pain endings (i.e. pepper)
An animal will automatically use what to help control the type of diet it eats?
taste preference
What does the taste preference change in regard with?
the body's need for certain specific substances
Explain the generation of nerve impulses of taste buds.
the first application of taste stimulus is a strong, immediate signal that is transmitted to nerve fibers. The exposed taste bus to taste stimulus has a weaker continuous signal
The intensity of sour taste sensation is approximately proportional to what?
the logarithm of the hydrogen ion concentration
What does the exact percentage of the number of people that exhibit taste blindness depend on?
the method of testing and the concentration of the substance
