The nose is the sense organ specialized in olfaction. It has specialized receptors responsible in generating impulses which are transmitted to the brain for interpretation. The presentation summarizes the anatomy and physiology of sense organ of smell.

1. THE SENSES
OF
SMELL
BY
J. MWELWA

2. GENERAL OBJECTIVES
At the end of the lecture, students should be able to
acquire knowledge and have the understanding on the
anatomy and physiology of the sense of olfactory.

3. SPECIFIC OBJECTIVES
At the end of the lesson the students should be able to:-
•Describe the anatomy of the nose.
-Blood supply.
-Nerve supply.
•State the functions of the nose.
•Explain the physiology of smell.

5. ANATOMY OF THE NOSE
• The nose consists of the external nose and the nasal
cavity,
• Both are divided by a septum into right and left
halves.

6. EXTERNAL NOSE
• The external part of the nose has a triangular or pyramidal shape,
with the highest point of it referred to as the apex or the tip of the
nose.
• The thin superior part that blends with the forehead is called the
root of the nose, while the region between the apex and the root
is called the dorsum.
• The small curve just beneath the root is known as the nose bridge.

8. EXTERNAL NOSE CONT’
• The external nose has also two elliptical orifices called
the naris (nostrils), which are separated from each
other by the nasal septum.
•The lateral margin, the ala nasi, is rounded and
mobile.

11. STRUCTURE CONT’
• The framework of the external nose above is made of
by the nasal bones, the frontal processes of the
maxillae, and the nasal part of the frontal bone.
• Below, the framework is formed of plates of hyaline
cartilage

13. Blood Supply of the External Nose
• The skin of the external nose is supplied by branches
of the ophthalmic and the maxillary arteries.
• The skin of the ala and the lower part of the septum
are supplied by branches from the facial artery.

14. Nerve Supply of the External Nose
• The infratrochlear and external nasal branches of the
ophthalmic nerve (CN V) and the infraorbital branch of
the maxillary nerve (CN V).

15. NASAL CAVITY
• The nasal cavity has
– a floor,
– a roof,
– a lateral wall,
– a medial or septal wall.

17. STRUCTURES CONT’
THE FLOOR OF NASAL CAVITY
• Palatine process maxilla
• Horizontal plate palatine bone

18. STRUCTURES CONT’
THE ROOF
• It is narrow.
• It is formed:
– anteriorly by the nasal and frontal bones,
– in the middle by the cribriform plate of the
ethmoid,
– posteriorly by the downward sloping body of the
sphenoid.

19. STRUCTURES CONT’
THE MEDIAL WALL OF NASAL CAVITY (The Nasal
Septum)
• Divides the nasal cavity into right and left halves
• It has osseous and cartilaginous parts

21. STRUCTURES CONT’
THE LATERAL WALLS OF NASAL CAVITY
• Marked by 3 projections:
– Superior concha
– Middle concha
– Inferior concha
• The space below each concha is called a meatus.
These are superior meatus, middle meatus and inferior
meatus.

24. BLOOD SUPPLY TO THE NASAL CAVITY
• From branches of the maxillary artery, one of the
terminal branches of the external carotid artery.
• The most important branch is the sphenopalatine
artery which branches of the facial artery in the region
of the vestibule.

25. NERVE SUPPLY OF THE NASAL CAVITY
• The olfactory nerves from the olfactory mucous
membrane ascend through the cribriform plate of the
ethmoid bone to the olfactory bulbs.

27. OLFACTORY NERVES (FIRST CRANIAL NERVES)
• These are the sensory nerves of smell. They originate
as specialized olfactory nerve endings
(chemoreceptors) in the mucous membrane of the
roof of the nasal cavity above the superior nasal
conchae.

28. OLFACTORY NERVE CONT’
• On each side of the nasal septum nerve fibres pass
through the cribriform plate of the ethmoid bone to
the olfactory bulb where interconnections and
synapses occur.

29. OLFACTORY NERVE CONT’
• 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.

30. FUNCTIONS OF THE NOSE
• Breathing
• Air conditioning of inspired air
• Protection of lower airway
• Ventilation and drainage of P.N.S.
• Olfaction
• Vocal resonance

31. PHYSIOLOGY OF SMELL
• 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.

32. PHYSIOLOGY CONT’
• The air entering the nose is warmed and convection
currents carry eddies of inspired air to the roof of the
nasal cavity. 'Sniffing' concentrates volatile molecules
in the roof of the nose.

33. PHYSIOLOGY CONT’
• This increases the number of olfactory receptors
stimulated and thus the perception of the smell. The
sense of smell may affect the appetite. If the odours
are pleasant the appetite may improve and vice versa.

34. PHYSIOLOGY CONT’
• When accompanied by the sight of food, an appetizing
smell increases salivation and stimulates the digestive
system.
• The sense of smell may create long-lasting memories,
especially to distinctive odours, e.g. hospital smells,
favorite or least-liked foods.

35. PHYSIOLOGY CONT’
• 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.

37. PHYSIOLOGY CONT’
• Adaptation. When an individual is continuously exposed to an
odour, perception of the odour decreases and ceases within a
few minutes. 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.

39. REFERENCES
• David S, Jackie B and Ricki L. (2003), Hole’s Essentials of Human
Anatomy and Physiology, International edition, McGraw-Hill Higher
Education, New York, USA.
• Roger Watson (2005), Anatomy and Physiology for Nurses, 20th
edition, Elsevier, Oxford, UK.
• Waugh A & Grant A (2001), ROSS AND WILSON Anatomy and
physiology in health and illness, 9th Ed, Church-Hill Livingstone,
Toronto.

40. THANK YOU