OLFACTION: SENSE OF SMELL – Human Anatomy and Physiology B. Pharma 1st Semester



At the end of this lecture, student will be able to

• Describe the anatomy of olfactory receptor

• Explain the physiology of olfaction and olfactory


• Anatomy of olfactory receptor

• Physiology of olfaction and olfactory receptor


• 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


• 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

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