Chapter 53

Question 1

What causes the sour sensation?

Answer 1

caused by acids, intensity of sourness is proportional to the H+ ion concentration.

Question 2

What causes the salty sensation?

Answer 2

caused by ionized salts, mainly sodium ion concentration, cations mainly responsible.

Question 3

What causes the sweet sensation?

Answer 3

not a single class, can be from sugars, alcohols, aldehydes, ketones, amides, basically all organic compounds. A simple change, like addition of a radical, can make it change from sweet to bitter.

Question 4

What causes the bitter sensation?

Answer 4

again similar to sweet, all organic compounds, but mainly, organic long chain substances that have nitrogen, and alkaloids (medicines, quinine, caffeine, nicotine). Deadly toxins contain alkaloids (and are bitter, so it helps with stopping us from eating toxins)

Question 5

What causes the umami sensation?

Answer 5

Japanese word meaning savory or delicious, has L-glutamate, receptors for L-glutamate cause this.

Question 6

What is the structure of the taste bud?

Answer 6

Taste bud is quite small (1/30 mm diameter, 1/16 mm length), and has about 50 cells, sustentacular cells which are supporting, and taste cells, which are being replaced often. There is an outer pore, microvilli inhabit this pore and provide the receptors a lot of surface area to taste nearby stuff.

Question 7

Outline hte neural pathway from the taste bud –> post central gyrus

Answer 7

ant 2/3 taste is on lingual n. –> corda tympani –> facial n. –> solitary tract –> solitary nucleus –> VPM –> post central gyrus

Question 8

What are olfactory cells?

Answer 8

primary receptor for smells, has olfactory cilia, projections that go into the mucus lining and react to odors which stimulate the olfactory cells.

Question 9

What are sustentacular cells?

Answer 9

supporting cells

Question 10

What is bowman’s gland?

Answer 10

secrete mucus on the surface of the olfactory membrane

Question 11

What are mitral cells?

Answer 11

receive information from the olfactory cell axons.

Question 12

Explain the transduction of smells into electrical signals

Answer 12

odor binds to olfactory cell –> Gs activation –> Na channels open –> stimulus

Question 13

How does odor adaptation occur?

Answer 13

Odor starts out strong then diminishes due to possibly inhibitory granule cells in the olfactory bulb, that use feedback inhibition to suppress strong smells. So it is not mainly the receptors, but CNS playing a large role, just like in the adaptation of taste

Question 14

What is the pathway of smell into the CNS?

Answer 14

olfactory cell –> olfactory bulb to terminate in mitral and tufted cells –> Lateral and medial olfactory areas

Question 15

The old olfactory pathway is associated with which olfactory area?

Answer 15

medial olfactory area

Question 16

What is the fxn of the medial olfactory area?

Answer 16

this pathway controls basic behaviors. Olfactory bulb sends the signals to the medial olfactory area, midbasal portions of the brain located anterior to the hypothalamus. Licking lips, salivation, feeding responses caused by food smell, and emotional drives related to smell are all processes associated with the medial olfactory area

Question 17

The new olfactory pathway is associated with which olfactory area?

Answer 17

Lateral Olfactory area

Question 18

What is the fxn of the lateral olfactory area?

Answer 18

comprised of the prepyriform and pyriform cortex, and the cortical portion of the amygdaloid nuclei (associated with limbic and hippocampus). This area is associated with memory formation of bad or good tastes, such as taste aversion. Also only place in the entire cerebral cortex where sensory signals pass directly into cortex without passing first through the thalamus.

Question 19

The newer olfactory pathway is associated with which olfactory area?

Answer 19

thalamus

Question 20

What is the fxn of the thalamus in smelling?

Answer 20

passes through the DM thalamic nucleus, then the lateroposterior quadrant of the orbitofrontale cortex, this helps in conscious analysis of odors (thinking about odors).