OLFACTION: SENSE OF SMELL
Objectives
At the end of this lecture, student will be able to
• Describe the anatomy of olfactory receptor
• Explain the physiology of olfaction and olfactory
transduction
Content
• Anatomy of olfactory receptor
• Physiology of olfaction and olfactory receptor
OLFACTION: SENSE OF SMELL
• Originates in the nasal cavity, which also acts as a passage for respiration
Anatomy of Olfactory Receptors
• Nose contains 10–100 million receptors for the sense of smell
• Contained within an area called the olfactory epithelium
Olfactory epithelium consists of three kinds of cells:
a) Olfactory receptors
b) Supporting cells
c) Basal cells
Olfactory receptors
• First-order neurons of the olfactory pathway
• Bipolar neuron with an exposed knob-shaped dendrite
• An axon projecting through the cribriform plate
• Ending in the olfactory bulb
• Olfactory hairs, cilia project from the dendrite
• Cilia responds to inhaled chemicals
• Produces a generator potential
• Initiates the olfactory response
Supporting cells
• Columnar epithelial cells of the mucous membrane lining the nose
• Provide physical support, nourishment, and electrical insulation for the olfactory receptors
• Detoxify chemicals that come in contact with the olfactory epithelium
Basal cells
• Stem cells located between the bases of the supporting cells
• Continually undergo cell division to produce new olfactory receptors
Olfactory (Bowman’s glands)
• Within the connective tissue; supports the olfactory epithelium
• Produce mucus
• Moistens the surface of the olfactory epithelium
• Dissolves odorants so that transduction can occur
Olfactory epithelium and olfactory receptors
Physiology of Olfaction – Olfactory pathway
• Olfactory receptors react to odorant molecules
• A generator potential (depolarization) develops and triggers one or more nerve impulses
• In some cases, an odorant binds to an olfactory receptor protein in the plasma membrane of an olfactory hair
• The olfactory receptor protein is coupled to a membrane protein called a G protein
• In turn activates the enzyme adenylate cyclase
Olfactory transduction
Summary
• Olfactory receptors are responsible for the sense of smell
• Cilia responds to inhaled chemicals; generates potential;
initiates the olfactory response; activates the enzyme adenylate cyclase