Humans have a very keen sense of smell: we can detect
thousands of different smells. This ability relies on the presence of special
sensory receptors in the upper part of the nose. When stimulated by odour
molecules, these receptors send signals along nerves to the brain for
processing. Sometimes odour molecules do not reach the sensory area, but
sniffing will help get them there.
SMELL RECEPTOR CELLS IN ROOF OF NOSE
Smell receptors are specialized nerve cells. Each bears many tiny
cilia (hairs), which project into the space in the upper part of the nose. A
nerve fibre extends from the other end of each cell. This joins other fibres to
form the olfactory nerves, which carry signals to the brain.
CILIA OF SMELL RECEPTOR CELL
The cilia can detect tiny amounts of substances in the air, though
molecules of those substances must first be absorbed by the mucus layer. There
they interact with the cilia to trigger nerve impulses.
