Taste and Smell

Taste

We have taste buds on our tongues.  Our tongues are covered with papillae that have taste buds.  Taste buds have clumps of microvilli on top, and join a sensory nerve on the bottom.  Each taste bud (cell) has its own microvilli with specific chemical receptors for different molecules.  The taste buds can generally sense the taste sensations of salt, sweet, bitter, and sour.  Despite these general categories of taste sensation, everyone's taste buds are not identical... and so we may not all appreciate sweet the same way, for example.  Alternately, some people may have more or fewer sweet taste buds.  Still others may have sweet taste buds that respond to different molecules than other people's sweet taste buds.  The bottom line is that no two people taste everything exactly the same way.

Smell

Humans can differentiate between about 1000-2000 odors.  Olfactory cells are sandwiched among columnar epithelial cells lining the roof of the nasal cavity.  The olfactory cells have hairlike extensions, known as sensory cilia, formed by the dendrites of the olfactory cells.  The sensory cilia project out into the mucus lining the nasal passage.  Here, the sensory cilia bind various molecules capable of activating the olfactory cells.  Once activated, the olfactory cells send action potentials along their axons and through the cribriform plate of the ethmoid bone.  The axons of the olfactory cells are bundled to form the "olfactory nerves" that pass through the holes (olfactory foramina) of the cribriform plate.  The olfactory cells synapse with nerves within the olfactory bulbs that sit right on top of the cribriform plate.  The olfactory tract carries information about smell to the olfactory cortex, bypassing the thalamus.  The olfactory cortex is located centrally, close to where the frontal and parietal lobes join.  Because our receptors for smell are located only in the uppermost region of the nasal passage, we can detect odors better by forcefully inhaling air in order to circulate odor causing molecules past the olfactory cilia... "whiffing, sniffing."