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1. NOSE
ANATOMY, FUNCTION & DIAGRAMS
Ravish Yadav

2. OLFACTION: SENSE OF SMELL
•Chemical senses
•The sensations arise from
• The interaction of molecules with smell receptors.
•Impulses for smell
• Propagate to the higher cortical areas.
•Certain odors and tastes
• Can evoke strong emotional responses or a flood of memories.

3. ANATOMY OF OLFACTORY RECEPTORS
•The nose contains
• 10–100 million receptors
• For the sense of smell or olfaction,
• Contained within an area called the olfactory epithelium.
•The olfactory epithelium
• Occupies the superior part of the nasal cavity.
•The olfactory epithelium consists of
• Three kinds of cells:
• Olfactory receptors, supporting cells, and basal cells

5. • Olfactory receptors are
• The neurons of the olfactory pathway.
• Each olfactory receptor is
• A bipolar neuron
• Projecting through the cribriform plate and ending in the olfactory bulb.
• The parts of the olfactory receptors
• That respond to inhaled chemicals
• The olfactory hairs, cilia that project from the dendrite.
• Chemicals that have an odor
• Can therefore stimulate the olfactory hairs are called odorants.
• Olfactory receptors respond to
• The chemical stimulation of an odorant molecule
• By producing a generator potential,
• Thus initiating the olfactory response.

7. SUPPORTING CELLS:
• Columnar epithelial cells of the mucous membrane lining the nose.
• Provide physical support, nourishment, and electrical insulation for the olfactory
receptors, and they help detoxify chemicals that come in contact with the olfactory
epithelium.
BASAL CELLS:-
• Are stem cells located between the bases of the supporting cells.
• They continually undergo cell division
• To produce new olfactory receptors,
• Which live for only a month or so before being replaced.

8. OLFACTORY (BOWMAN’S) GLANDS:
• Produce mucus
• That is carried to the surface of the epithelium by ducts.
• The secretion moistens
• The surface of the olfactory epithelium and dissolves odorants so that transduction can occur.
OLFACTORY NERVES:-
• Both supporting cells of the nasal epithelium and olfactory glands
• Innervated by branches of the facial (VII) nerve,
• which can be stimulated by certain chemicals.
• Impulses in these nerves
• Stimulate the lacrimal glands in the eyes and nasal mucous glands.
• The result is tears and a runny nose after inhaling substances such as pepper or the
vapors of household ammonia.

9. PHYSIOLOGY OF OLFACTION
• Olfactory receptors
• React to odorant molecules.
• A generator potential (depolarization) develops
• 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,
• which in turn activates the enzyme adenylate cyclase .
• The result is the following chain of events:
• Production of cyclic adenosine monophosphate (cAMP) : opening of sodium ion (Na)
channels : inflow of Na : depolarizing generator potential : generation of nerve
impulse and propagation along axon of olfactory receptor.

10. Odourant + receptor protein

Activation of G protein

Activation of adenylate
cyclase

ATP  cAMP

Opening of Na+ channels

Na+ influx

depolarization
MECHANISM OF OLFACTORY CELL STIMULATION

13. THE OLFACTORY PATHWAY
• On each side of the nose,
• Bundles of the slender, unmyelinated axons of olfactory receptors
• Extend through about 20 olfactory foramina in the cribriform plate of the ethmoid
bone.
• These bundles of axons
• Collectively form the right and left olfactory (I) nerves.
• The olfactory nerves
• Terminate in the brain in paired masses of gray matter
• Called the olfactory bulbs,
• Which are located below the frontal lobes of the cerebrum.
• Within the olfactory bulbs,
• The axon terminals of olfactory receptors
• Form synapses with the dendrites and cell bodies of olfactory bulb neurons.

15. • Axons of olfactory bulb neurons
• Extend and form the olfactory tract.
• Some of the axons of the olfactory tract
• Project to the primary olfactory area of the cerebral cortex;
• Where conscious awareness of smell begins.
• Other axons of the olfactory tract
• Project to the hypothalamus;
• These connections account for our emotional and memory-evoked responses to
odors.
• From the primary olfactory area,
• Pathways also extend to the frontal lobe.
• An important region for odor identification and discrimination is the orbitofrontal
area.