The Sense of Scents.
Like the sense of taste, the sense of smell is a chemical sense. The ability to smell odors is called olfaction, or the olfactory sense.
Our smelling function is carried out by two small odour-detecting patches – made up of about five or six million yellowish cells – high up in the nasal passages.
The part of the olfactory system that transduces odors—turns odors into signals the brain can understand—is located at the top of the nasal passages. This area of olfactory receptor cells is only about an inch square in each cavity yet contains about 10 million olfactory receptors.
OLFACTORY RECEPTOR CELLS -The olfactory receptor cells each have about a half dozen to a dozen little “hairs,” called cilia that project into the cavity. Like taste buds, there are receptor sites on these hair cells that send signals to the brain when stimulated by the molecules of substances that are in the air moving past them.
THE OLFACTORY BULBS – The olfactory bulbs are located right on top of the sinus cavity on each side of the brain directly beneath the frontal lobes. The olfactory receptors send their neural signals directly up to these bulbs, bypassing the thalamus, the relay center for all other sensory information. The olfactory information is then sent from the olfactory bulbs to higher cortical areas, including the primary olfactory cortex (the piriform cortex),the orbitofrontal cortex, and the amygdala.
The Human Nose
The human nose is in fact the main organ of taste as well as smell. The so-called taste-buds on our tongues can only distinguish four qualities – sweet, sour, bitter and salt -all other ‘tastes’ are detected by the olfactory receptors high up in our nasal passages.
The nose has special receptors that are sensitive to odor molecules travelling through the air. These receptors are very tiny, and there are about 10 million of them in your nose. There are hundreds of different receptors, and each one can sense certain odors. These signals are then sent to the brain, which puts the signals together and tells you what you smell. The brain, working with the nose, can recognize over 10,000 different smells.