<P> In vertebrates, smells are sensed by olfactory sensory neurons in the olfactory epithelium . The olfactory epithelium is made up of at least six morphologically and biochemically different cell types . The proportion of olfactory epithelium compared to respiratory epithelium (not innervated, or supplied with nerves) gives an indication of the animal's olfactory sensitivity . Humans have about 10 cm (1.6 sq in) of olfactory epithelium, whereas some dogs have 170 cm (26 sq in). A dog's olfactory epithelium is also considerably more densely innervated, with a hundred times more receptors per square centimeter . </P> <P> Molecules of odorants passing through the superior nasal concha of the nasal passages dissolve in the mucus that lines the superior portion of the cavity and are detected by olfactory receptors on the dendrites of the olfactory sensory neurons . This may occur by diffusion or by the binding of the odorant to odorant - binding proteins . The mucus overlying the epithelium contains mucopolysaccharides, salts, enzymes, and antibodies (these are highly important, as the olfactory neurons provide a direct passage for infection to pass to the brain). This mucus acts as a solvent for odor molecules, flows constantly, and is replaced approximately every ten minutes . </P> <P> Taste is the sensation produced when a substance in the mouth reacts chemically with taste receptor cells located on taste buds in the oral cavity, mostly on the tongue . 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 gustatory cortex is responsible for the perception of taste . </P> <P> 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 . </P>

Where are the receptors for special senses located