Taste And Smell

Question 1

Structure of olfactory tissue:

Answer 1

• taste is a function of chemoreceptors of the taste buds
• densely distributed along the surface papillae of the tongue

Question 2

What is the circumvallatae papillae?

Answer 2

• contains a large number of taste buds
• arranged in a V shape on the posterior surface of the tongue

Question 3

What

Question 4

What are the fungi form papillae?

Answer 4

• contains moderate numbers of taste buds and is located near the tip of the tongue
• moderate numbers of taste buds are also located along the foliate papillae
• located in the folds along the lateral surfaces of the tongue

Question 5

What are taste buds composed between?

Answer 5

• 40-60 modified epithelial cells
• some are chemosensitive = taste cells
• supporting cells
• basal cells

Question 6

What are the taste cells continuously replaced by?

Answer 6

• mitotic division of the surrounding epithelial basal cells
• they are arranged amount a minute taste pore

Question 7

What does each taste cell have?

Answer 7

• has a tuft of microvilli or gustatory hairs that protrude into the taste pore
• exposing them to the chemicals = taste molecules
• these microvilli provide the receptor surface for taste
• the taste cell is a modified epithelial cell which synapses with a sensory nerve fibre at its base

Question 8

What is the membrane potential of the taste cells?

Answer 8

• negatively charged on the inside with respect to the outside

Question 9

What happens as a taste chemical reacts with the villi?

Answer 9

• the cell will become depolarised
• which passes the signal onto the sensory nerve fibres at their base
• the taste chemical itself is washed away by saliva

Question 10

What is the rate of discharge of the nerve fibres from taste buds?

Answer 10

• rises to a peak within a small fraction of a second
• adapts within a few seconds back to a lower, steady level
• as long as the taste stimulus remains

Question 11

What is sour taste?

Answer 11

• caused by acids and the more acidic the food, the stronger the sensation becomes

Question 12

What is salty taste?

Answer 12

• elicited by ionized salts, mainly by the sodium chloride concentration
• the quality of taste varies between salts and the cations of salts, are responsible for salty taste
• anions also contribute

Question 13

What is sweet taste?

Answer 13

• not caused by a single class of chemicals
• sugars, glycols, alcohols
• organic chemicals
• if their chemical structure changes, it can turn into a bitter taste

Question 14

What is a bitter taste?

Answer 14

• almost entirely organic substances
• not caused by a single type of chemical agent
• two classes of substances likely to cause bitter sensations = long chain organic substances that contain nitrogen and alkaloids
• bitter taste = high intensity = individual can reject the foot
• important feature as many deadly toxins found in plants are alkaloids

Question 15

What is umami taste?

Answer 15

• delicious
• dominant taste of food containing L-glutamate = meat extracts

Question 16

Taste pathways to the CNS:

Answer 16

• taste buds on the anterior two thirds of the tongue pass first into the lingual nerve then onto the facial nerve to the brainstem
• taste buds from the posterior third are transmitted through the glossopharyngeal nerve
• these nerves carry signals to the posterior brainstem in the nucleus of the solitary tract, which is in the medulla oblongata
• signals travel to other parts of the brain associated with taste
  = hypothalamus, amygdala, thalamus & gustatory cortex of the parietal lobe

Question 17

What is the hypothalamus for?

Answer 17

• autonomic reflexes
• salivation
• gagging, vomiting

Question 18

What is the amygdala for?

Answer 18

• emotional responses

Question 19

What is the gustatory cortex for?

Answer 19

• conscious perception of taste

Question 20

What is taste preference?

Answer 20

• associated with mechanisms in the CNS
• an animal will choose certain types of food over others to help control the diet it eats
• animals that are salt, calcium or glucose depleted choose drinking water with a high conc of sodium chloride over pure water
• and the sweetest foods

Question 21

What are the sensory organs for smells made from?

Answer 21

• olfactory cells
• which form a patch of epithelium known as the olfactory mucosa in the roof of the nasal cavity

Question 22

What are olfactory cells?

Answer 22

• bipolar nerve cells
• the neck and the head of the cell are modified dendrite with a swollen tip, forming a knob which possesses olfactory cilia
• these hairs project into the mucus that coats the inner surface of the nasal cavity
• the basal end forms an axon
• axons of many cells join together to form small fascicles which leave the nasal cavity through pores in the bone surrounding it

Question 23

What happens when olfactory fibres exit through the bone surrounding the nasal cavity?

Answer 23

• they enter a pair of olfactory bulbs beneath the frontal lobe of the brain
• the axons of neurons leaving the olfactory bulbs form bundles called the olfactory tracts
• these tracts lead to the olfactory cortex of the temporal lobes of the brain, leading to the conscious sensation of smell

Question 24

When can odours be detected?

Answer 24

• once dissolved in the mucus layer
• they bind with cilia membrane receptors and excite the cell, generating and transmitting action potentials to the CNS
• by way of the olfactory nerve

Question 25

Olfactory pathways to the CNS:

Answer 25

- olfactory bulb - olfactory tract - olfactory cortex of the temporal lobes = conscious sensation of smell - hippocampus & amygdala - when can a loss of smell and taste occur? = when the nasal cavity is inflamed due to respiratory infection, smoking & cocaine