Question

1. What is  primary taste sensation, and the major type of receptors.
2. Distinguish between static and dynamic equilibrium. Know major structures involved in each. Know what they monitor.
3. Receptors for hearing are located in the cochlea. What is the function of cochlear hair cells? What membrane layer supports them? Which membrane to the hair cells bend against?
4. Know roles of rods and cones in the eye. Where exactly are they found and in what concentration? What is the significance of the optic disc?
5. Know the eye structure where the most light refraction takes place.

Answer 1

1Q).

The sense of taste is perceived by tongue though the taste buds, the receptors of taste. In a taste bud, the taste cells are located in the center (but not at the end). The taste buds consists of,

· Groups of gustatory receptor cells or taste cells (modified epithelial cells)

· Supporting cells (sustain the taste cells)

· Basal cells (act as neural stem cells)

The gustatory receptor cells contain microvilli or gustatory hairs that projects to the epithelial surface through taste pore. These gustatory hairs (the actual taste receptors) are stimulated (depolarisation) by the presence of chemicals in solution form (tastant).

The gustatory receptors are G-protein coupled receptors (GPCRs). The binding of taste producing chemicals to the receptors initiate the process of sense of taste. Depending upon the nature and concentration of chemical bound, the receptor potential is generated.

Taste buds are present at the sides and base of the tongue, which can sense five tastes namely,

1. Sweet (felt at the tip)

2. Bitter (felt at the back)

3. Sour (felt at the back edge)

4. Salt (felt at the front edge)

5. Umami (savoriness)

Sweet receptors respond to the sugars such as sucrose, glucose. Some of the amino acids and lead salts also stimulate these receptors (Eg: table sugar).

Sour receptors are activated by hydrogen ions and blockade of sodium or potassium ion channels (Eg: orange).

Salty taste is elicited mainly by the influx of metal ions such as sodium ions through the sodium channels (Eg: table salt).

Bitter taste receptors respond to the alkaloids such as caffeine (Eg: amla, coffee).

Umami taste is elicited by the substances such as glutamate, which gives meat taste when added to the food materials (Eg: meat).