Smell

1. Mucociliary Blanket of Nose and Paranasal Sinuses
Physiology of Smell
Capt; Pyae Htay Oo
PG-1
ORL-HNS
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2. Functions of noseTION OF NOSE
1. Respiration
2. Air-conditioning of inspired air
3. Protecting of lower airway ( mucociliary mechanism )
4. Vocal resonance
5. Nasal reflex function
6. Olfaction
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3. Lining Membranes of internal Nose
1. Vestibule – It is lined by skin and contains hairs,hair follicles and
many sebaceous glands.
2. Olfactory region- upper one third of lateral wall ( up to superior
concha ),corresponding part of nasal septum and roof of nasal cavity
form olfactory region.Here, mucous membrane is olfactory neuro-
epithelium and pale in color.
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4. 3.Respiratory region-Lower two third of nasal cavity form the
respiratory region.
-Here, mucous membrane shows variable thickness being thickest over
the nasal conchae, especially at their end, and
-Quite thick over the nasal septum but very thin in the meatuses and
floor of the nose.
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5. -It is highly vascular and also contains erectile tissues.It’s surface is
lined by pseudostratified ciliated columner epithelium which contains
plenty of goblet cells.
-In the submucous layer of mucous membrane are situated serous,
mucous,both serous and mucous secreting glands, the ducts of which
open on the surface of mucosa.
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8. Respiratory and Olfactory Membranes
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9. Protection of lower Airway
(1)Mucociliary mechanism
Nasal mucosa is rich in goblet cells, secreting glands both mucous
and serous.
Their secretion forms a continuous sheet called mucous blanket
spread over the normal mucosa.
Mucous blanket consists of superficial mucous layer and a deep
serous layer.
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11.  Mucociliary flow is the main mechanical defence of the nasal mucosa
because it physically cleans inspired air.
 Mucus flows from the front of nose to posterior.
 Mucus from the sinus joins the stream on lateral wall.
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12.  This stream flows through the middle meatus and then around the E
tube orifice before being swallowed.
 The mucociliary transport system is made up of cilia of the respiratory
epithelium as well as a mucous blanket.
 Floating on the top of cilia are constantly beating to carry it like a
‘conveyer belt’ toward the nasopharynx.
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13. Figure . “Conveyor belt” mechanism of mucus blanket to entrap and carry organisms and
dust particles.
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14.  Mucous blanket moves at a speed of 5–10 mm/min and the complete
sheet of mucus is cleared into the pharynx every 10–20 min.
 Presence of turbinates is almost double the surface area to perform this
function and about 600–700 mL of nasal secretions are produced in 24
hr.
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15.  Viscoelastic properties enable it to trap larger particles.
 This mechanical defence is predominant and expels filtered particles
and debris into the nasopharynx and oropharynx as well as elimination
through sneezing and coughing.
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16. Ciliary action
 Beat frequency of cilia in body temp – 7-16 Hz
 It remains constant between 32 – 40℃
 In mammals, cilia beat 10-20 times per second at room temperature.
 They have a rapid propulsive/effective stroke and a slow recovery
stroke.
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17.  During propulsive phase, cilia are straight & tip engaged the viscous
layer of mucus blanket.
 During recovery phase,cilia are bent over & lie in aqueous layer.
 The mucous blanket is propelled backward by metachronous
movement of cilia.
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18.  In immotile cilia syndrome, cilia are defective and cannot beat
effectively, leading to stagnation of mucous in the nose and paranasal
sinuses and bronchi causing chronic rhinosinusitis and bronchiectasis.
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19. Factors affecting ciliary action
 Drying, Excessive heat or cold
- stop the ciliary action.
- below 10℃ & >45 ℃, ciliary movements stop.
 Isotonic saline
- preserved ciliary action but
solution >5% & <2% paralysis of ciliary movement.
 Infections, allergy
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20.  pH
- cilia beat above pH 6.4
- cilia beat function slightly in alkaline pH 8.5
 Drugs
-neurotransmitter – acetylcholine -↑ the rate
- adrenaline - ↓ the rate
 Smoking, Noxious fumes like sulfur dioxide and carbon dioxide
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21. Cilia
• The ultrastructure of all cilia remains the same , but nasal cilia are
short.
• The surface membrane of a cilium encloses an organized
ultrastructure.
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22. • The nine outer-paired microtubules enclose a single inner pair of
microtubules.
• The outer pairs of microtubules are linked to one another by nexins
and to the inner pair of microtubules by central spokes.
• In addition, outer pairs of microtubules have both outer and inner
dynein arms that are made up of an ATPase.
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23. Fig. Ultrastructure of cilia
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24. (2)Enzymes and immunoglobulins
 Nasal secretions also contain an enzyme called muramidase (lysozyme)
which kills bacteria and viruses.
 Mucus consists of compounds that are able to neutralize antigens through
innate mechanisms, learned, and adaptive immunological responses.
 Immunoglobulin A (IgA) and immunoglobulin E (IgE) are found on the
surface, and they act whenever the mucosa is breached.
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25.  In most cases, bacterial allergens are destroyed, but there are other viruses
and bacteria that require the activation of the cell-mediated immune
responses.
 IgA is the main immunoglobulin in secretions and has distinctive
characteristics.
 IgA has two subgroups, namely IgA1 and IgA2. IgA1 with a monomeric
structure, is frequent in serum while IgA2 with a dimer structure, is
common in nasal secretions.
 Immunoglobulin A constitutes 70% of the total proteins in nasal secretions.
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26. (3) Sneezing
 It is a protective reflex.
 Foreign particles which irritate nasal mucosa are expelled by sneezing.
 Copious flow of nasal secretions that follows irritation by noxious
substances helps to wash them out.
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27.  The pH of nasal secretion is nearly constant at 7.
 The cilia and the lysozyme act best at this pH.
 Alteration in nasal pH, due to infections or nasal drops, seriously
impairs the functions of cilia and lysozyme.
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28. Olfaction(Physiology of Smell)
 Smell is important for pleasure and for enjoying the taste of food.
 When nose is blocked, food tastes bland and unpalatable.
 Vapours of ammonia are never used to test the sense of smell as they
stimulate fibres of the trigeminal nerve and cause irritation in the nose
rather than stimulate the olfactory receptors.
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29. Olfactory Region
• Olfactory region – Upper one-third of lateral wall of nasal cavity (upto
superior turbinate), corresponding part of nasal septum, and roof of
nasal cavity
Aera:200-400mm² with a density of approximately 5×10 receptor
cells/mm²
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31. Olfactory Epithelium
• Lies in the superior part of each nasal cavity.
• Within this epithelium, contains 10-1000 million olfactory receptors.
• The olfactory epithelium consists of three kinds of cells:
1.olfactory receptors cells
2.supporting cells or sustentacular cells
3.basal cells
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32. (1) Olfactory receptors
• They are actually bipolar nerve cells derived from the CNS.
• There are about 100 million of these cells in the olfactory epithelium.
• The mucosal end of the olfactory cell forms a knob.
• From knob,4-25 olfactory cilia project into the mucus that coats the
inner surface of nasal cavity.
• These projecting cilia form a dense mat in the mucus.
• These cilia react to odours in the air and stimulate the olfactory cells.
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33. (2) Supporting cells
• The receptors cells in the olfactory epithelium are interspersed among
supporting cells or sustentacular cells.
• Supporting cells are columnar epithelial cells.
• They provide physical support, nourishment and electrical insulation
for olfactory receptors.
• They help detoxify chemicals that come in contact with the olfactory
epithelium.
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34. (3)Basal cells
• Basal cells are stem cells located between the bases of the supporting
cells.
• They continually undergo cells division to produce new olfactory
receptors, which live for only a month or so before being replaced.
• This process is remarkable – olfactory receptors are neurons, and
mature neurons are generally not replaced.
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35. Bowman’s glands and Olfactory mucus
• The space among the olfactory cells in the olfactory membrane are
many small Bowman’s glands that secrete mucous onto the surface of
the olfactory membrane— mucus is carried out 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.
• When odorants molecules reach olfactory region, must interact with
mucus overlying the receptor cells, produced by Bowman’s glands and
adjacent respiratory mucosa (goblet cells).
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36. • Adrenergic, cholinergic, and peptidergic agents change the properties
of mucus overlying the olfactory receptors.
• In the olfactory mucus-epithelial system, clearing odorants is equall as
important as absorption.
• Olfactory mucus may exert a differential role in deactivating,
removing, or desorbing odorants from the olfactory area.
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39. Excitation of olfactory cells
• The portion of each olfactory cell that respond to the olfactory
chemical stimuli is the olfactory cilia.
• The odorant substance on coming in content with the olfactory
membrane surface, first diffuses into the mucous that covers the cilia.
• Then, it binds with receptor proteins in the membrane of each cilium
and couples to G-protein.
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40. • Olfaction is mediated by G-protein coupled receptors in the cells which
interact with a specific adenyl cyclase within neuroepithelium.
• Stimulus (odours)>> Receptors(G-protein coupled receptor cell
protein)>> cAMP pathway>> opening Na ion channels>> action
potential>> excitation the olfactory neuron>> Olfactory nerve>> CNS
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41. Olfactory Pathway
• Olfactory nerves -They carry sense of smell and supply olfactory
region of nose. They are the central filaments of the olfactory cells and
are arranged into 12–20 nerves which pass through the cribriform
plate and end in the olfactory bulb.
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42. • Cribriform plate has multiple small perforation through which an equal
number of small nerves pass upward from the olfactory membrane in the
nasal cavity to enter the olfactory bulb in the cranial cavity.
• Olfactory bulb lies over the cribriform plate, separating the cranial cavity
from the upper nasal cavity.
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43. • Both olfactory bulb and tract are anterior outgrowth of brain tissue
from the base of the brain.
• Short axons from the olfactory cells terminate in multiple globular
structures within the olfactory bulb called glomeruli.
• Each glomerulus is the terminus for dendrites from about 25 large
mitral cells and about 60 smaller tufted cells, the cell bodies of which
lie superior to the glomeruli in the olfactory bulb.
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44. • Mitral and tufted cells send axons through the olfactory tract to
transmit olfactory signals to higher levels in the CNS.
• Mucus-cilia >>> Olfactory receptor cells >>> Axons of these cells>>>
Glomeruli in olfactory bulb>>> Dendrites of mitral & tufted cells in
bulb>>> Axons of mitral and tufted cells in tract>>> CNS.
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46. CNS Smell Pathway
• Olfactory tract enters the brain at the anterior junction between the
mesencephalon and cerebrum.
• There, olfactory tract divides into two pathways;
• Medially –the medial olfactory area(stria)of the brain stem-(very old
olfactory system)
• Laterally- the lateral olfactory area(stria)- newer and less old system
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47. • Very old olfactory system ,
-medial olfactory stria >>Septal nuclei >>Hypothalamus (limbic
system)
-more primitive responses to olfaction ,salivation ,liking lips and
primitive emotional drives to smell.
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48. • Lateral olfactory area-anteromedial portion of the temporal lobe (cerebral
cortex)
• Less Old Olfactory System,
-This is the only area of the entire cerebral cortex where sensory signals pass
directly to the cortex without passing first through the thalamus.
- Prepyriform and pyriform cortex plus portion of amygdaloid
nuclei>>limbic system (hippocampus)
- Learn control of food intake and aversion to food that have caused
nausea and vomiting
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49. • The newer pathway,
- passes through the thalamus passing to the dorsomedial thalamic
nucleus >>orbitofrontal cortex.
- Conscious perception and analysis of odour (odour discrimination)
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50. Olfactory Pathway
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54. Disorders of Smell
 It is essential for the perception of smell that the odorous substance be
volatile and that it should reach the olfactory area unimpeded.
 The healthy state of olfactory mucosa and the integrity of neural pathways,
i.e. olfactory nerves, olfactory bulb and tract and the cortical center of
olfaction are necessary.
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55. Anosmia is total loss of sense of smell while hyposmia is partial loss.
 They can result from nasal obstruction due to nasal polypi, enlarged
turbinates or oedema of mucous membrane as in common cold,
allergic or vasomotor rhinitis.
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56. Parosmia is perversion of smell; the person interprets the odours
incorrectly.
Often these persons complain of disgusting odours.
It is seen in the recovery phase of postinfluenzal anosmia.
Intracranial tumour should be excluded in all cases of parosmia.
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57. Olfactometry(Odour Measurement)
• Qualitative olfactometry ,
-Olfactory sense is assessed by taking a solution.
-Following primary odours are usually tested :
1.Etherial –ether 2.Camphoraceous –camphor
3.Flora 1-salicyldehyde 4.Musky-phenyl acetic acid
5.Minty –mint 6.Pungent –formalin
7.Putrid-thiophenol
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58. Quantitative Olfactometry
-Measurement of olfactory sense is done with an olfactometer.
-Olfactometry gives information about the following:
1.The extent of the field of smell
2.Gives an idea about patient’s acuity of smell
3.Possible parosmia(perverted smell)
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59. THANKS FOR YOUR ATTENTION
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