The nose has many specialized smell-detecting cells with nerves taking information to the brain. Each cell has up to 25 tiny micro-hairs that respond to minute odour particles.
The tongue is not the only place where taste buds are to be found. They are also on the gums, inner lips, cheek linings and other parts of the mouth.
The average 25-year-old has up to 10,000 taste buds. After the age of 50, however, taste buds gradually die, and a 70-year-old may have only 5,000 taste buds left. This explains why foods lose their taste as you get older.
Smell or olfactory sense has peripheral receptor located in the nasal mucosa. The olfactory mucosa has high sensitivity to concentration of chemicals. The smell sensation in human is strong due to well develop of the olfactory apparatus and it varies with individuals. There are two types of cells in olfactory mucosa, namely, sustentacular cells and receptor cells (Fig 45a). The receptor cells are actually bipolar nerve cells and they are dispersed among the sustentacular cells. The central process of the receptor cell, called axon, travels deep into the olfactory mucosa and then combines with other axons to form olfactory nerve. The olfactory cells form knob like structures called olfactory vessels from which large number of hair like structures that project into the mucous coat on the inner surface of the nostril. Besides the olfactory cells there are Bowman’s glands that are responsible for the secretion of mucous.
The substances that are volatile in nature, partially soluble in water and soluble in lipid media are capable to stimulate olfactory receptor cells. The olfactory cells react to the olfactory stimuli to generate receptor potential (impulse) in the olfactory nerve.