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Physiology of smell
- 1. Olfaction Uthiravelu. P Tutor Department of Physiology
- 2. Introduction • Olfaction • Chemoreceptors • Macrosmatics • Microsmatics Site of olfaction • Olfactory epithelium • Vomeronasal organ • Olfactory receptor cell
- 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 cribriform plate of ethmoid bone and enter olfactory bulbs
- 7. Olfactory Pathways 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 Propyl mercaptan 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