The olfactory epithelium contains 10-20 million olfactory receptor neurons that detect odors. The dendrites of these bipolar neurons form olfactory rods containing cilia that project into the nasal mucus. The vomeronasal organ detects pheromones and sends signals to the amygdala and hypothalamus. While once thought vestigial in humans, it is now known to detect human pheromones at low concentrations. Different odors are detected at very low concentrations, with some detectable at only a few parts per million or less. Olfactory receptors can rapidly adapt to odors within a minute.

2.  SITUATED IN OLFACTORY MUCUS MEMBRANE
 CONSISTS 10 TO 20 MILLIONS OF OLFACTORY
RECEPTORS SUPPORTED BY SUSTENTACULAR
CELLS.
 MUCOSAALSO CONTAINS MUCUS – SECRETING
BOWMAN GLANDS
 OLFACTORY RECEPTOR CELL
BIPOLAR NEURON
DENTRITIE OF THE NEURON ARE SHORT
THE EXPANDED END CALLED OLFACTORY ROD.

3.  OLFACTORY ROD ABOUT 10-12 CILLIA
 THE CILLIA ARE NON MYELINATED,
 THE LENGTH OF 2MU
 DIAMETER -0.1MU
VOMERONASAL ORGAN
 Accessory olfactory organ
 Discovered in 1813 by danish physician ludwig jacobson
 it is aslo called jacobson organ
 The organ enclosed in a cartilagious capsule
 And opens into a base of nasal cavity
 vmno helps the animals to detect and trace quantities of
chemicals
 Which send the impulses from this organ to amyglada and
hypothalamus via accessory olfactory bulb.

4.  Vestigial or non functional
 Recently found in the anterior part of nasal
septum
 Receptors of vomeronasal pit detect odorless
human pheromones or vomeropherins at very
low concentration.
 The subconscious detection of odourless
chemical messengers in air considered as a
sixth sense in human being.

10. Aromatic or resinous camphor – lavender –clove- bitter
almonds
Ambrosial –Musk
Burning odor-tobacco –roasted coffee-meat
ethereal = fruits-ether-beeswax
Fragrant or balsamic = flower and perfumes
Garlic odor – caporic acid and sweet cheese
Nauseating odor – decayed vegtables and feces
Repulsive odor – bed bug

11. Ethyl ether
5.8mg/l
Chloroform
3.3mg/l
Pepermint oil
0.02 mg/l
Butyric acid
0.009mg/l
Artificial musk
0.00004mg/l
Methyl
mercaptan
0.0000004 mg/l
Air

12.  Its are phasic receptors
 Adapt very rapidly < 1 min
 Adaptation occurs up to 50%

13.  Anosmia- complete loss of sensation of smell
 Hyperanosmia-incresed or exaggerated
olfactory sensation
 Also called olfactory hyperperesthesia
 Occurs in brain damage, epilepsy and
neurotic condition
 Hypoanosmia-Reduced ability to recognise &
detect the smell
 Permanent & temporary