Taste and Smell

Dr Taha Sadig Ahmed

Taste, gustatory perception, or gustation[1] is the sensory impression of food or other substances on the tongue and is one of the five traditional senses.Taste is the sensation produced when a substance in the mouth reacts chemically with taste receptor cells located on taste buds.

. Taste, along with smell (olfaction) and trigeminal nerve stimulation (registering texture, pain, and temperature), determines flavors of food or other substances. Humans have taste receptors on taste buds (gustatory calyculi) and other areas including the upper surface of the tongue and the epiglottis.

• The tongue is covered with thousands of small bumps called papillae,

• which are visible to the naked eye.

• Within each papilla are hundreds of taste buds.

• The exception to this is the filiform papillae that do not contain taste buds.

• There are between 2000 and 5000 taste buds that are located on the back and front of the tongue.

• Others are located on the roof, sides and back of the mouth, and in the throat.

• Each taste bud contains 50 to 100 taste receptor cells.

Olfaction is the sense of smell.This sense is mediated by specialized sensory cells of the nasal cavity .In humans, olfaction occurs when odorant مصدرة molecules bind to specific sites on the olfactory للرائحةreceptors These receptors are used to detect the presence of smell. They come together at the glomerulus The glomerulus a structure which transmits signals to the olfactory bulb (a brain structure directly above the nasal cavity and below the frontal lobe). Olfaction, along with taste, is a form of chemoreception. The chemicals themselves that activate the olfactory system, in general at very low concentrations, are called odorants.

• The binding of the ligand (odor molecule or odorant) to the receptor leads to an action potential in the receptor neuron, via a second messenger pathway,

• depending on the the odorants stimulate adenylate cyclase to synthesize cAMP via a G protein

• called Golf.

• (2) cAMP, which is the second messenger here, opens a cyclic nucleotide-gated ion channel (CNG), (3) producing an influx of cations (largely Ca2+ with some Na+) into the cell, slightly depolarising it.

• (4) The Ca2+ in turn opens a Ca2+-activated chloride channel, (5) leading to efflux of Cl−, (6) further depolarizing the cell and triggering an (7) action potential.

• Ca2+ is then extruded through a sodium-calcium exchanger.

• A calcium-calmodulin complex also acts to inhibit the binding of cAMP to the cAMP-dependent channel, thus contributing to olfactory adaptation.