Physiology of smell

Physiology of smell

1. Olfaction
Uthiravelu. P
Tutor
Department of Physiology

2. Introduction
•Olfaction
•Chemoreceptors
•Macrosmatics
•Microsmatics
Site of olfaction
•Olfactory epithelium
•Vomeronasalorgan
•Olfactory receptor cell

3. Olfactory Mucosa

5. Olfactory epithelium
•Each neuron has a
thick dendrite with an
expanded end called
olfactory rod
•From rods, cilia project
to the mucous surface
•Each receptor neuron
has 10-20 cilia
•Axons of olfactory
receptor neurons
pierce cribriformplate
of ethmoidbone and
enter olfactory bulbs

7. OlfactoryPathways
Olfactory nerve
Olfactory bulb
Olfactory Glomeruli
Olfactory tract
Cortical olfactory areas

12. Transduction in olfactory receptor
neurons
•Binding of odourant
molecule to receptor
•Activation of
receptor
•Depolarization of
receptor potential
•Action potential
Processing of
olfactory
sensation in bulb

13. Transmission of information to cortex &
neocortex

14. Olfactory thresholds and discrimination
•Olfactory receptors
respond only to
substances in contact
with olfactory
epithelium and need to
be dissolved in mucus
•Humans can recognize
more than 10,000
different odors
Substance mg/L of Air
Ethyl ether 5.83
Chloroform 3.30
Pyridine 0.03
Oil of peppermint 0.02
Iodoform 0.02
Butyric acid 0.009
Propylmercaptan 0.006
Artificial musk 0.00004
Methyl mercaptan 0.0000004

15. Abnormalities
•Anosmia–absence of sense of smell
•Hyposmia–diminished olfactory
sensitivity
•Dysosmia–distorted sense of smell
•More than 75% of humans over the age
of 80 have an impaired ability to identify
smells