This document discusses the anatomy and physiology of the sense of smell. It describes how olfactory nerves originate in the nasal cavity and transmit signals to the olfactory bulb and olfactory cortex. It explains that smell detection works as volatile molecules stimulate olfactory receptors in the nose. Factors like sniffing, inflammation, and adaptation can impact one's sense of smell.

1. ANATOMY AND PHYSIOLOGY
OF SENSE OF SMELL
PREPARED BY:
USHA RANI KANDULA,
ASSISTANT PROFESSOR,
DEPARTMENT OF ADULT HEALTH NURSING,
ARSI UNIVERSITY,ASELLA,ETHIOPIA,
SOUTH EAST AFRICA.

2. •The nasal cavity has a dual function: a
passageway for respiration and sense of smell.

4. OLFACTORY NERVES
•OLFACTORY NERVES (FIRST CRANIAL NERVES)
•These are the sensory nerves of smell.

5. •They originate as specialised olfactory nerve
endings (chemoreceptors) in the mucous
membrane of the roof of the nasal cavity above
the superior nasal conchae.

6. •On each side of theThe olfactory structures an
enlarged section of the olfactory apparatus in
the nose and on the inferior surface of the
cerebrum.

7. •Nasal septum nerve fibres pass through the
cribriform plate of the ethmoid bone to the
olfactory bulb where interconnections and
synapses occur.

8. •From the bulb, bundles of nerve fibres form
the olfactory tract which passes backwards
to the olfactory area in the temporal lobe of
the cerebral cortex in each hemisphere
where the impulses are interpreted and
odour perceived.

9. PHYSIOLOGY OF SMELL

10. PHYSIOLOGY OF SMELL
•The sense of smell in human beings is generally
less acute than in other animals.

11. •Many animals are known to secrete odorous
chemicals called pheromones that play an
important part in chemical communication
in, for example, territorial behaviour, mating
and the bonding of mothers and their
newborn offspring.

12. •The role of pheromones in human
communication is unknown.

13. • All odorous materials give off volatile molecules,
which are carried into the nose with the inhaled air
and stimulate the olfactory chemoreceptors when
dissolved in mucus.

14. •The air entering the nose is warmed and
convection currents carry eddies of inspired air
to the roof of the nasal cavity.

15. •'Sniffing' concentrates volatile molecules in the
roof of the nose. This increases the number of
olfactory receptors stimulated and thus the
perception of the smell.

16. •The sense of smell may affect the appetite.
• If the odours are pleasant the appetite may
improve and vice versa.

17. •When accompanied by the sight of food, an
appetising smell increases salivation and
stimulates the digestive system.

18. •The sense of smell may create long-lasting
memories, especially to distinctive odours, e.g.
hospital smells, favourite or least-liked foods.

19. •Inflammation of the nasal mucosa prevents
odorous substances from reaching the olfactory
area of the nose, causing loss of the sense of
smell (anosmia).
•The usual cause is the common cold.

20. ADAPTATION.
•When an individual is continuously exposed to
an odour, perception of the odour decreases
and ceases within a few minutes.

21. •This loss of perception only affects that specific
odour and adaptation probably occurs both in
the cerebrum and in the sensory receptors in
the nasal cavity.

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