It contains 50 million bipolar olfactory
sensory neurons mixed with
It is the place where nervous system is
closest to the external world.
New sensory neurons are generated by
Basal stem cells.
Epithelium is covered by mucus secreted
by Bowman glands and supporting cells .
7PHYSIOLOGY OF OLFACTION
Each sensory neuron terminates in to a
knob which contain CILIA.
Cilia are unmyelinated processes that
protrude in to mucus.
Odorant molecules dissolve in the
mucus and bind to receptors.
Mucus provides appropriatr molecular
and ionic environment for odour
8PHYSIOLOGY OF OLFACTION
The axons pass through cribriform plate
and enter the olfactory bulb.
Mitral cells , tufted cells ,meet the axons
in bulb to form glomeruli.
9PHYSIOLOGY OF OLFACTION
neurons which connect glomeruli .
Granule cells-no axons ,reciprocal
connections with mitral and tufted cells.
Mitral and tufted cells secrete
glutamate and granule cells secrete
Epithelium also contains the
trigeminal pain fibers .
10PHYSIOLOGY OF OLFACTION
The axons of the mitral and tufted cells
pass through lateral olfactory stria to
terminate on the dentrides of the olfactory
Olfactory cortex contains :-
anterior olfactory nucleas ,olfactory
tubercle, piriform cortex , amygdala
11PHYSIOLOGY OF OLFACTION
From olfactory cortex it goes the orbitofrontal
complex which is generally greater on right side thus
the representation of olfaction is asymmetric.
12PHYSIOLOGY OF OLFACTION
REPRODUCTIVE AND INGESTIVE
BEHAVIOUR Ex:-pregnancy block in rat
13PHYSIOLOGY OF OLFACTION
There is evidence for existence of phermones in
humans and there is a close relationship between
smell and sexual function.
Sense of smell is more acute in females more at
the time of ovulation.
14PHYSIOLOGY OF OLFACTION
HOW IT CAN DISCRIMINATE 10000
15PHYSIOLOGY OF OLFACTION
There are approxiamately 500
olfactory genes which constitute 2%of
The amino acid sequences of
receptors is very diverse ,but all are G-
protein coupled receptors.
The GPCR contains three sub units
When a chemical attaches these
dissociate and α activates adenylate
cyclase to catalyze the production of
cAMP . 16PHYSIOLOGY OF OLFACTION
The result is inward directed calcium
current which produces graded receptor
This opens the calcium activated chloride
channels further depolarising the cell due to
high intra cellular chloride levels.
If the stimulus is sufficient for the receptor
potential to exceed its threshold,an action
potential is triggered.
Each neuron projects to one/two glomeruli.
Lateral inhibition – sharpens the olfactory
signals 17PHYSIOLOGY OF OLFACTION
ODOR DETECTION THRESHOLD
ODORANT BINDING PROTEINS
Long term adaptation:cGMP
Short term adaptation:cAMP
18PHYSIOLOGY OF OLFACTION
19PHYSIOLOGY OF OLFACTION