Chemoreception – Olfaction and
Gustation
Olfactory organs
Olfaction
• Contain olfactory epithelium with olfactory
receptors, supporting cells, basal cells
– Olfactory receptors are modified neurons
• Surfaces are coated with secretions from
olfactory glands
• Olfactory reception involved detecting dissolved
chemicals as they interact with odorant binding
proteins
The Olfactory Organs
Olfaction
• Specialized neurons present in the
olfactory epithelium in the nose.
• They project cilia into a mucus
layer. The cilia are able to bind to
odorant molecules  the binding
triggers an AP which is
transmitted to the olfactory area
of the olfactory bulb  olfactory
cortex (lower frontal area and
limbic system of the brain
• Each olfactory receptor is
specialized for 1 odorant molecule
Olfaction
• Olfactory pathways
– No synapse in the thalamus for arriving information
• Olfactory discrimination
– Can distinguish thousands of chemical stimuli
• CNS interprets smells by pattern of receptor activity
– Olfactory receptor population shows considerable
turnover
– Number of receptors declines with age
Gustation
Taste receptors
• Clustered in taste buds
• Associated with lingual papillae
Taste buds
• Contain basal cells which appear to be stem cells
• Gustatory cells extend taste hairs through a
narrow taste pore
Gustatory Reception
Gustatory pathways
• Taste buds are monitored by cranial nerves
– Synapse within the solitary nucleus of the medulla
oblongata
– Then on to the thalamus and the primary sensory cortex
Gustatory discrimination
• Primary taste sensations
– Sweet, sour, salty, bitter
– Receptors also exist for umami and water
• Taste sensitivity shows significant individual
differences, some of which are inherited
• The number of taste buds declines with age
Taste
• Receptors for taste are
modified epithelial cell
present in taste buds
located on the tongue,
roof of the mouth and
pharynx
Taste receptors
Neural pathway
• Taste impulses travel through nerves VII, IX
and X to a gustatory nucleus in the medulla
oblongata (cross over)  thalamus 
gustatory cortex located in the parietal lobe in
the mouth area.
• What is the flavor of food?