SlideShare une entreprise Scribd logo
1  sur  92
Télécharger pour lire hors ligne
Physiology of Olfaction
Dr. Jinu V Iype
1st year Post Graduate
Department of ENT
Reference from Cummings
Otorhinolaryngeology book
INTRODUCTION
• Senseof smell has been recently heavily
studied because of it’s importance to
human being’s survival.
• It helps to track food , can alert us
todanger like gasleak, fire, rotten
food.
• It is also linked to brain that
process emotion and memory.
Olfaction or Olfactory perception
- the sense of smell mediated by a group
of specialised sensory cells in nasal cavity.
Odour
-the property of a substance which gives it
a particular smell.
Anatomy of Olfactory Stimulation
1.Nasal Passageways
• Olfactory nerve (cranial nerve I) stimulation,
which is necessary for identification of most
odorants, depends on the odorant molecules’
reaching the olfactory mucosa at the top of the
nasal cavity.
• Although molecules can reach the olfactory
cleft by diffusion, essentially olfaction requires
some type of nasal airflow.
• During eating, there is a retro nasal flow of
odorant molecules that stimulate the olfactory
receptors at the top of the nose and contribute
greatly to the flavor of the food.
Swallowing and Deglutition
Retronasal Airflow
Production of flavour from swallowed
food Adds Smell to Taste
• At physiologic
airflow rates,
approximately 50%
of the total airflow
passes through the
middle meatus,
• ~ 35% flowing
through the inferior
meatus
• About 15% flows
through the olfactory
region
• Sniffing is an almost universally performed
maneuver when a person is presented with an
olfactory stimulus.
• It increase the number of olfactory molecules
in the olfactory cleft by means of a transient
change in the airflow pattern of the nose.
• A sniff also may allow the trigeminal nerve to
alert the central olfactory neurons that an
odorant is coming.
Physiology of olfaction
• For molecules to reach the olfactory area, they
must pass through the tall but narrow nasal
passageways.
• The epithelium lining the walls of these
passageways is wet, has variable thickness.
2. Olfactory Mucus
• After the odorant molecules reach the olfactory
region, they must interact with the mucus
overlying the receptor cells.
• The mucus apparently comes from both
Bowman’s glands deep in the lamina propria
(only of serous type in humans) and the
adjacent respiratory mucosa (goblet cells)
• To reach the olfactory
receptors, the odorant
molecules must be
soluble in the mucus.
• Changes in the
thickness or
composition of the
mucus can influence
the diffusion time
required for odorant
molecules to reach the
receptor sites
• Once in the olfactory mucus-epithelial system,
the rate at which the odorant is cleared also is
important.
• Studies shows that 79% of a radioactively
labeled odorant (butanol) remained trapped in
the mucus 30 minutes after inspiratory
exposure, whereas radioactively labeled octane
cleared rapidly.
3. Olfactory Epithelium
• Located 7 cm inside the nasal cavity, the
olfactory sensory neurons are protected in a 1-
mm-wide crevice of the postero superior nose.
• At the epithelial surface, these bipolar neurons
are exposed to
the outside world
through their
dendrites
and cilia.
• A number of research groups have shown that
there is mixing of olfactory and respiratory
epithelial tissues in adult.
• The number of these clumps of respiratory
epithelium, which are found in the olfactory
area, increases with age, suggesting that a loss
of primary olfactory neurons at least partially
explains the decreased olfactory ability
associated with aging.
Low magnification of the surface of the nasal cavity taken from a transition
region.
Patches of respiratory (R) epithelium (dark areas) can be seen within the
olfactory (O) region
Low-power three-dimensional scanning view of the olfactory epithelium and lamina
propria. The olfactory epithelium (E) overlies a thick connective tissue lamina propria
that contains olfactory axon fascicles (A x) and blood vessels (V) (×248).
• The human
olfactory
epithelium covers
an area of roughly
1 cm2 on each
side.
• The epithelium is
pseudostratified
columnar, and it
rests on a
vascular lamina
propria with no
submucosa
Physiology of olfaction
• This portion of mucosa can be readily
identified from the rest of the nasal mucosa by
its unique yellowish color.
Embryologically
• Olfactory receptors derive from neuroblasts.
These neuroblasts differentiates to form
olfactory placodes.
• The central part of each placode invagiantes
giving rise to olfactory sac.
• Olfactory sac opens anteriorly
• Olfactory organ
is the only part of
the body in which
the cell bodies of
neurons lie at the
surface, directly
in contact with
the external
environment.
four main cell types
1. ciliated olfactory receptors
2. microvillar cells
3. supporting (sustentacular) cells
4.basal cells
The olfactory receptor neuron
• Bipolar
• Club-shaped peripheral “knob” that bears the
cilia.
• Extends odourant receptor-containing cilia
into mucus.
• olfactory nerve 15 to 20 foramina in the
cribriform plate to synapse in the bulb
High-power magnification of an olfactory knob with long cilia
gradually tapering as they extend over the epithelial surface. At
the base of individual cilia, a necklace-like structure (arrow) can
be seen on the surface of the olfactory knob
• Allison et al estimate the rabbit to have
approximately 50 million olfactory axons,
whereas Jafek estimates humans to have only
6 million bilaterally.
• The olfactory ensheathing cells are unique in that
they share characteristics that are common with
Schwann cells and central glial cells.
• Because olfactory neurons - ability to regenerate
and make functional synapses with the olfactory
bulb.
• possible therapeutic potential for repair of
peripheral neuronal injury.
• potential agents for reversing spinal cord injuries
and demyelinating diseases.
The microvillar cell
• one tenth as often as the ciliated olfactory
neurons.
• flask-shaped, is located near the epithelial
surface, and has an apical membrane
containing microvilli that project into the
mucus overlying the epithelium
• The deep end of the cell tapers to a thin, axon-
like cytoplasmic projection that proceeds into
the lamina propria.
• Low-power
magnification of
fractured olfactory
epithelium
illustrating the axon-
like processes
(arrows) from
microvillar cells (M),
which extend basally
between supporting
cells
SUPPORTING CELLS/SUSTENTACULAR
CELLS
• Tall cells have an apical
membrane that joins
tightly with the surface
of the receptor cells and
the microvillar cells.
• Do not generate action
potentials, nor are they
electrically coupled to
each other
• Play a role in ion and
water regulation and,
along with
Bowman’s gland
duct cells, contain
xenobiotic enzymes
such as cytochrome
P-450 that likely
contribute to odorant
metabolism.
Cross-sectional view
of the olfactory
epithelium showing
the columnar
supporting cells (S)
that extend the full
length of the
epithelium. An
olfactory neuron (O)
with its dendrite and
basal cell (B) can be
seen among
supporting cells
BASAL CELLS
• Sit along the basal lamina.
• Two groups of replicating cells
Horizontal basal cells Globose basal cells
are just above positioned between
the basal lamina the horizontal basal
cells & immature
neurons.
•The globose basal cells seem to be responsible
for the continuous replacement of olfactory
receptor neurons
• During severe insult
→repopulate the
nonneuronal components
of the epithelium .
• The replication cycle is
between 3 and 7 weeks.
• When the new receptor
cell forms, it also projects
its axon to the olfactory
bulb, where it synapses
with second-order
neurons, thereby ensuring
continual olfactory
function and continual
olfactory neuron
replacement.
Vomeronasal Organ
• Many mammals have an identifiable pit or groove
in the anteroinferior part of the nasal septum that
contains chemosensitive cells.
• In most of these animals,
a nerve can be identified
connecting these cells to
the central nervous system,
to an accessory olfactory
bulb.
• Biopsy studies of the nasal mucosa in the small
pit often seen along the anteroinferior nasal
septum (Jacobson’s organ) show olfactory-like
histology but no central connection.
• Electrical activity
elicited by certain
compounds directly
delivered to the
vomeronasal area has been
shown to cause changes in
blood pressure, heart rate,
and hormonal levels.
• It is believed to detect
external chemical
signals called
pheromones.
• These signals, which are
not detected
consciously as odors by
the olfactory system,
mediate human
autonomic,
psychological, and
endocrineresponses.
Olfactory Bulb
• Located directly over the cribriform plate.
• first relay station in the olfactory pathway
where the primary olfactory neurons synapse
with secondary neurons.
Neural components
are arranged in six concentric layers:
the olfactory nerve
 glomerular
External plexiform
 mitral cell
 internal plexiform
granule cell
The receptor cell axons
of the olfactory nerve
layer →the glomeruli
→ synapse with the
dendrites of the
mitral and tufted
cells within the
spherical glomeruli.
These second order
cells, in turn, send
collaterals that synapse
within the periglomerular
and external plexiform
layers, resulting in
“reverberating” circuits
in which
negative and positive
feedback occur.
mitral cells modulate their
own output by activating
granule cells (which are
inhibitory to them).
• The mitral and
tufted cell axons
project
ipsilaterally to the
primary olfactory
cortex via the
olfactory tract
Olfactory tract enters brain 2 pathways
Lateral
Olfactory stria
Medial
Olfactory stria
Physiology of olfaction
MEDIAL OLFACTORY AREA
• consists of a group of nuclei
• located in the mid basal portions of the brain
immediately
• Contain septal nuclei-
feed into the hypothalamus
and other primitive
portions of the brain’s
limbic system
Composed of
prepyriform
pyriform cortex
cortical portion of amygdaloid nuclei.
signal pathways- almost all portions of
limbic system , especially hippocampus-
important for learning like or dislike for
food stuffs.
An important feature of the lateral olfactory area is
that many signal pathways from this area also feed
directly into an older part of the cerebral cortex
called the paleocortex in the anteromedial
portion of the temporal lobe.
This is the only area of the entire cerebral
cortex where sensory signals pass directly to the
cortex
without passing first through the thalamus.
• The mitral and tufted cell axons project
ipsilaterally to the primary olfactory cortex via
the olfactory tract without an intervening
thalamic synapse
Primary olfactory cortex is comprised of the
Anterior Olfactory Nucleus - Pyriform Cortex-
Olfactory tubercle - Entorhinal area - Amygdaloid
Cortex - Corticomedial nuclear group of amygdala.
Anterior Olfactory Nucleus
Coordination of inputs from
contalateral olfactory cortex
Transfer of Olfactory memories from one
side to other
Pyriform Cortex
Olfactory discrimination
Amygdala
Emotional response to olfactory stimuli
Entorhinal Cortex
Olfactory Memories
Physiology of olfaction
Olfactory pathway
• First order neuron :
olfactory Epithelium to glomerulus
• Second order neuron :It is formed of the cells of
the olfactory bulb (mitral cells & Tufted cell)
Passes centrally as the olfactory tract .
• Third order neuron: Pyriform Cortex(Area 28)
contain primary olfactory cortex, which contain
3rd order neuron
Physiology of olfaction
Very Old Olfactory System
•More primitive responses to olfaction
salivation, primitive emotional drives to
smell
Less Old Olfactory System
• Learned control of food intake
• Aversion to food that have caused nausea &
vomiting
Newer System
• Odour discrimintation & analysis of odour
Olfactory Transduction and Coding
• Once the odorant molecule is dissolved in the
olfactory mucus
• Soluble binding proteins, like odorant-binding
protein -> enhance the access of odorants to the
olfactory receptors.
• Same odorant-binding protein molecules act to
remove odorant molecules from the region of
the receptor cell after transduction.
• The actual transformation of odorant chemical
information into an electrical action potential
occurs as a result of specific interactions
between odorant molecules and receptor
proteins on the surface of olfactory cilia.
• With the binding of the receptor to an odorant,
adenylate cyclase is activated by G protein–
coupled receptors and converts adenosine
triphosphate (ATP) into cyclic adenosine
monophosphate( cAMP).
• The cAMP then binds to a Na, Ca ion channel
to allow influx of these ions.
• As more channels open, the cell depolarizes,
and an action potential is produced
• Once the peripheral olfactory receptor cells are
depolarized, there begins a convergence of
electrical information toward the olfactory
bulb → glomeruli and mitral / tufted cells of
the olfactory bulb → Olfactory cortex
Molecular structure – Moncrieff 1967
Electrochemical Reactions
Stereospatial patterns
Molecular Properties
Olfactory mucus morphology
MOLECULAR STRUCTURE
• By Moncrieff 1967
• Suggested that molecular structure is
important.
• No stereospecific olfactory receptors have
been demonstrated.
Odour mol + Receptor  Photochemical reaction 
SIGNALTRANSDUCTION
Receptors containing carotenoids
By Briggs and Duncan,1962
By Mozell, 1970
Certain receptors could have a
stereospatial, lock and key form,
and receptor cells fire when the
surface membrane is altered.
LOCK KEY
Confirmationalchange
in receptor+mol
complex
SIGNAL
TRANSDUCTION
By Laffort et al,1974
Molecular properties depends on
-molecular volume at boiling point
-proton affinity and donation,
-local polarization within the molecule.
Holley and Doving,1977
Nature of smell - Pattern of stimulus within
mucosal configuration of receptor cells
This theory is based on
specific receptor sites &
on their position within olfactory mucosa
 Vibration Theory
 Olfactory Pigment Theory
 Enzyme Theory
 Penetrating and Puncturing theory
Randerbrock 1968
Olfactory perceptors are peptide chains vibrating
in an alpha helix.
Odourant molecules forms a band with peptide
chain modulating the vibration-transmitted to
nerves.
Pigment Theory
Rosenberg 1968
odourant molecule + olfactory pigment- increased
electrical conductivity
By Davies
Odourant molecules penetrate membrane
of olfactory receptor cell- diffuse-leaving a
hole.
Leakage of Sodium & pottasium occurs-
nerve impulse
OLFACTORY DYSFUNCTION
Anosmia
Hyposmia Hyperosmia
Phantosmia
OlfactoryAgnosia
Cacosmia /Parosmia /Troposmia
Presbyosmia Osmophobia
TYPESOF OLFACTORY DYSFUNCTION
o Anosmia-absenceof smell
o Hyposmiamicrosmia- diminished olfactorysensitivity
o Dysosmia-distorted senseof smell
o Phantosmia- perception of anodorant when noneis
presentl / Olfactory hallucination.
o Agnosia-inability to classify,contrast, or identify odor
sensationsverbally, eventhough the ability to distinguish
between odorants maybenormal
o Hyperosmia-Abnormally acute smell function (Rare
condition )
CLASSIFICATION& ETIOLOGY
• TRANSPORT OLFACTORY LOSS
Olfactory dysfunctions canbe causedby conditions
that interfere with the accessof the odorant to
the olfactory neuro-epithelium due to either
swollen nasalmucous membrane, structural
changesand/or mucussecretion.
Causes-Allergy rhinitis, Bacterial rhinitis and
sinusitis, Congenital abnormality like
encephalocele, Deviated NasalSeptum, Nasal
neoplasms, Nasalpolyps, Nasal surgery,Old age,
Viral infections.
• SENSORY OLFACTORY LOSS
Olfactory dysfunctions can be caused by
conditions that damage to the
neuroepithelium.
Causes-Drugs that affect cell turn over and
inhalations of toxic chemicals, viral
infections, neoplasms, radiation therapy.
• NEURAL OLFACTORY LOSS
• Olfactory dysfunctions canalso be causedby
conditions that damagethe central olfactory
pathways.
• Causes-AIDS,Alzheimer’s disease,Alcoholism,
Chemical Toxins,Cigarette smoke,Diabetes
Mellitus, Depression, Drugs, Huntington’s chorea,
Hypothyroidism, Kallmann syndrome, Korsakoff
psychosis,Malnutrition, Neoplasm, Neurosurgery,
Parkinson disease,Trauma,Vitamin B12def., Zinc
deficiency
APPROACHTO OLFACTORY DYSFUNCTION
A.DETAILEDMEDICALHISTORY
Onset, course, nature of impairment, their previous illness
andthen medications taken.
B. PHYSICALEXAMINATION
Thorough ENT,head and neck examinations including nasal
endoscopy. Aneurological examination emphasizing the
cranial nerves, cerebellar and sensorimotor function is
essential.
Psychological examination like general mood and check
for signsof depression should bedone.
C.LABORATORYFINDINGS
• Biopsy of olfactory neuroepithelium can be done
in rarecases
D.IMAGING
• Coronal CTscanand MRI Brain are useful.
sudden olfactory loss suggests
the possibility of head trauma, infection,
ischemia, or a psychogenic condition.
Gradual loss
the development of degenerative processes,
progressive obstructive lesions or tumors
within the olfactory receptor region or more
central neural structures.
Intermittent loss can be indicative
of an intranasal inflammatory process.
• A family history of smell dysfunction may
suggest
a genetic basis
Kallmann’s syndrome :
Delayed puberty in associationwith anosmia
(with or without midline craniofacial
abnormalities, deafness, and renal anomalies
Quantitative Olfactory Testing
(1)verify the validity of the patient’s complaint,
(2)characterize the exact nature and degree of the
problem,
(3) accurately monitor changes in function over
time
(4) detect malingering,
(5)obtain an objective basis for determining
compensation for disability.
UNIVERSITYOFPENNSYLVANIA
SMELLIDENTIFICATIONTEST
(UPSIT)
• Most commonly used & most superiorand reliable
test.
• Self-administered in 10-15minutes
• Scoredin <1 minute by non-med person
• Available in variouslanguages
• 40 “scratch & sniff “ patches
• Pt. choosesfrom 4 answers& must choose1
• Candetect malingering
• Dysfunction classified asNormosmia, anosmia, mild,
moderate or severe microsmia, or probable malingering
UPSIT
To assess olfaction unilaterally, the naris
contralateral to the tested side should
be occluded without distorting
the nasal valve region. This can be easily
accomplished
by sealing the contralateral naris using a
piece of MicrofoamTM.
The patient is instructed to sniff the
stimulus normally and to exhale through
the mouth.
Such occlusion not only prevents air from
entering the olfactory cleft from the
contralateral naris
Olfactory event-related potentials (OERPs)
• synchronized brain electroencephalographic
(EEG) activity induced by repeated pulsatile
presentations of an odorant is isolated from
overall EEG activity
Used as :-
sensitive and useful in detecting malingering
ELECTRO-OLFACTOGRAM
(EOG)
• Detected via an electrode placed on the surface
of the olfactory neuroepithelium
DIFFERENTIALDIAGNOSIS
• At present, no psychophysical methods to
differentiate sensory from neural hearingloss.
• History of olfactory lossgivesan important clues
tothe cause.
• Leadingcausesof olfactory dysfunctions are
head trauma and viral infections.
• Headtrauma are more common causeof anosmia
in children and young adults whereas viral
infectionsare more common causein older
adults.
• Congenital anosmia occurs in Kallmann syndrome
and also in albinism.
• Meningioma of inferior frontal region is the
most common neoplastic causeof anosmia.
• Dysomiais associatedwith depression.
TREATMENT
• Transport olfactory loss
Thefollowing treatments are effective
in restoring senseof smell:
i. Allergy management
ii. Antibiotic therapy
iii. Topicaland systemic glucocorticoid
therapy
iv. Operations for nasalobstruction.
• Sensorineural Olfactory loss.
No treatment with demonstrated
efficacyfor Sensorineural Olfactory
loss. Fortunately, spontaneous
recovery occurs.
Someclinicians advocate zinc and
vitamin therapy espVitaminA.
Physiology of olfaction

Contenu connexe

Tendances

Anatomy of inner ear by Dr. Aditya Tiwari
Anatomy of inner ear by Dr. Aditya TiwariAnatomy of inner ear by Dr. Aditya Tiwari
Anatomy of inner ear by Dr. Aditya TiwariAditya Tiwari
 
Physiology and theories of olfaction
Physiology and theories of olfactionPhysiology and theories of olfaction
Physiology and theories of olfactionLakhan M S
 
Olfactory system
Olfactory system Olfactory system
Olfactory system Usra Hasan
 
Physiology of deglutition by Dr.Ashwin Menon
Physiology of deglutition by Dr.Ashwin MenonPhysiology of deglutition by Dr.Ashwin Menon
Physiology of deglutition by Dr.Ashwin MenonDr.Ashwin Menon
 
Pterygopalatine fossa and approaches by Dr.Ashwin Menon
Pterygopalatine fossa and approaches by Dr.Ashwin MenonPterygopalatine fossa and approaches by Dr.Ashwin Menon
Pterygopalatine fossa and approaches by Dr.Ashwin MenonDr.Ashwin Menon
 
Special Senses - Organ of Corti
Special Senses - Organ of CortiSpecial Senses - Organ of Corti
Special Senses - Organ of CortiDr. Suhail Ahmad
 
Physiology of taste
Physiology of tastePhysiology of taste
Physiology of tasteNarmathaN2
 

Tendances (20)

Taste
Taste Taste
Taste
 
Anatomy of olfactory system
Anatomy of olfactory systemAnatomy of olfactory system
Anatomy of olfactory system
 
Taste pathway
Taste pathwayTaste pathway
Taste pathway
 
Anatomy of inner ear by Dr. Aditya Tiwari
Anatomy of inner ear by Dr. Aditya TiwariAnatomy of inner ear by Dr. Aditya Tiwari
Anatomy of inner ear by Dr. Aditya Tiwari
 
Physiology and theories of olfaction
Physiology and theories of olfactionPhysiology and theories of olfaction
Physiology and theories of olfaction
 
SENSE OF SMELL
SENSE OF SMELLSENSE OF SMELL
SENSE OF SMELL
 
Olfactory system
Olfactory system Olfactory system
Olfactory system
 
Olfactory system and functioning in human
Olfactory system and functioning in humanOlfactory system and functioning in human
Olfactory system and functioning in human
 
Olfaction
OlfactionOlfaction
Olfaction
 
Olfaction ppt
Olfaction pptOlfaction ppt
Olfaction ppt
 
physiology of smell
physiology of smell physiology of smell
physiology of smell
 
Physiology of deglutition by Dr.Ashwin Menon
Physiology of deglutition by Dr.Ashwin MenonPhysiology of deglutition by Dr.Ashwin Menon
Physiology of deglutition by Dr.Ashwin Menon
 
Auditory physiology of Inner Ear
Auditory physiology of Inner EarAuditory physiology of Inner Ear
Auditory physiology of Inner Ear
 
Olfactory pathway
Olfactory pathwayOlfactory pathway
Olfactory pathway
 
Pterygopalatine fossa and approaches by Dr.Ashwin Menon
Pterygopalatine fossa and approaches by Dr.Ashwin MenonPterygopalatine fossa and approaches by Dr.Ashwin Menon
Pterygopalatine fossa and approaches by Dr.Ashwin Menon
 
Special Senses - Organ of Corti
Special Senses - Organ of CortiSpecial Senses - Organ of Corti
Special Senses - Organ of Corti
 
Physiology of deglutition
Physiology of deglutitionPhysiology of deglutition
Physiology of deglutition
 
Pterygopalatine fossa
Pterygopalatine  fossaPterygopalatine  fossa
Pterygopalatine fossa
 
Taste physiology beba
Taste physiology bebaTaste physiology beba
Taste physiology beba
 
Physiology of taste
Physiology of tastePhysiology of taste
Physiology of taste
 

Similaire à Physiology of olfaction

physiology of smell and applied aspects of smell
physiology of smell and applied aspects of smellphysiology of smell and applied aspects of smell
physiology of smell and applied aspects of smellshama praveen
 
Physiology of olfaction
Physiology of olfactionPhysiology of olfaction
Physiology of olfactionKarthik Raja
 
Nose anatomy & physiology sensory system
Nose anatomy & physiology sensory systemNose anatomy & physiology sensory system
Nose anatomy & physiology sensory systemPooja Rani
 
Smell & Taste theory updated on 2021 BY PANDIAN M.
Smell & Taste theory updated on 2021 BY PANDIAN M. Smell & Taste theory updated on 2021 BY PANDIAN M.
Smell & Taste theory updated on 2021 BY PANDIAN M. Pandian M
 
Smell and taste by Pandian M. Dept of Physiology, DYPMCKOP,MH
Smell and  taste by Pandian M. Dept of Physiology, DYPMCKOP,MHSmell and  taste by Pandian M. Dept of Physiology, DYPMCKOP,MH
Smell and taste by Pandian M. Dept of Physiology, DYPMCKOP,MHPandian M
 
Lect 14 nose &amp; tongue (smell and taste sensation)
Lect 14 nose &amp; tongue (smell and taste sensation)Lect 14 nose &amp; tongue (smell and taste sensation)
Lect 14 nose &amp; tongue (smell and taste sensation)Ayub Abdi
 
Chemical senses- Sameena Latheef
Chemical  senses- Sameena LatheefChemical  senses- Sameena Latheef
Chemical senses- Sameena LatheefSameena Latheef
 
Peripheral Nervous System
Peripheral Nervous SystemPeripheral Nervous System
Peripheral Nervous SystemFulchand Kajale
 
Balance for artifact
Balance for artifactBalance for artifact
Balance for artifactzs4033bn
 
Cranial nerves Not directly associated with the eye
Cranial nerves Not directly associated with the eyeCranial nerves Not directly associated with the eye
Cranial nerves Not directly associated with the eyeOthman Al-Abbadi
 

Similaire à Physiology of olfaction (20)

olfaction.pptx
olfaction.pptxolfaction.pptx
olfaction.pptx
 
physiology of smell and applied aspects of smell
physiology of smell and applied aspects of smellphysiology of smell and applied aspects of smell
physiology of smell and applied aspects of smell
 
Physiology of olfaction
Physiology of olfactionPhysiology of olfaction
Physiology of olfaction
 
Nose
NoseNose
Nose
 
Olfaction.pptx
Olfaction.pptxOlfaction.pptx
Olfaction.pptx
 
Nose anatomy & physiology sensory system
Nose anatomy & physiology sensory systemNose anatomy & physiology sensory system
Nose anatomy & physiology sensory system
 
12
1212
12
 
Physiology of smell
Physiology of smellPhysiology of smell
Physiology of smell
 
Olfaction mbbs
Olfaction mbbsOlfaction mbbs
Olfaction mbbs
 
Smell & Taste theory updated on 2021 BY PANDIAN M.
Smell & Taste theory updated on 2021 BY PANDIAN M. Smell & Taste theory updated on 2021 BY PANDIAN M.
Smell & Taste theory updated on 2021 BY PANDIAN M.
 
11 respiratory system
11  respiratory system11  respiratory system
11 respiratory system
 
olfactory nerve
olfactory nerveolfactory nerve
olfactory nerve
 
Smell and taste by Pandian M. Dept of Physiology, DYPMCKOP,MH
Smell and  taste by Pandian M. Dept of Physiology, DYPMCKOP,MHSmell and  taste by Pandian M. Dept of Physiology, DYPMCKOP,MH
Smell and taste by Pandian M. Dept of Physiology, DYPMCKOP,MH
 
Lect 14 nose &amp; tongue (smell and taste sensation)
Lect 14 nose &amp; tongue (smell and taste sensation)Lect 14 nose &amp; tongue (smell and taste sensation)
Lect 14 nose &amp; tongue (smell and taste sensation)
 
Chemical senses- Sameena Latheef
Chemical  senses- Sameena LatheefChemical  senses- Sameena Latheef
Chemical senses- Sameena Latheef
 
Peripheral Nervous System
Peripheral Nervous SystemPeripheral Nervous System
Peripheral Nervous System
 
Balance for artifact
Balance for artifactBalance for artifact
Balance for artifact
 
Cranial nerves Not directly associated with the eye
Cranial nerves Not directly associated with the eyeCranial nerves Not directly associated with the eye
Cranial nerves Not directly associated with the eye
 
Special senses
Special sensesSpecial senses
Special senses
 
I.t. elective presentation
I.t. elective presentationI.t. elective presentation
I.t. elective presentation
 

Plus de Jinu Iype

Autoimmune inner ear disease(AIED)
Autoimmune inner ear disease(AIED)Autoimmune inner ear disease(AIED)
Autoimmune inner ear disease(AIED)Jinu Iype
 
Cerebrospinal fluid rhinorrhea (CSF)
Cerebrospinal fluid rhinorrhea (CSF)Cerebrospinal fluid rhinorrhea (CSF)
Cerebrospinal fluid rhinorrhea (CSF)Jinu Iype
 
Robotic surgery in ENT
Robotic surgery in ENTRobotic surgery in ENT
Robotic surgery in ENTJinu Iype
 
Anatomy of Skullbase
Anatomy of SkullbaseAnatomy of Skullbase
Anatomy of SkullbaseJinu Iype
 
Anatomy & physiology of thyroid gland
Anatomy & physiology of thyroid glandAnatomy & physiology of thyroid gland
Anatomy & physiology of thyroid glandJinu Iype
 
Narrow band imaging
Narrow  band imagingNarrow  band imaging
Narrow band imagingJinu Iype
 
Trauma to the face
Trauma to the faceTrauma to the face
Trauma to the faceJinu Iype
 
Anatomy of larynx
Anatomy of larynxAnatomy of larynx
Anatomy of larynxJinu Iype
 
Anatomy of Lateral wall of nose
Anatomy of Lateral wall of noseAnatomy of Lateral wall of nose
Anatomy of Lateral wall of noseJinu Iype
 

Plus de Jinu Iype (9)

Autoimmune inner ear disease(AIED)
Autoimmune inner ear disease(AIED)Autoimmune inner ear disease(AIED)
Autoimmune inner ear disease(AIED)
 
Cerebrospinal fluid rhinorrhea (CSF)
Cerebrospinal fluid rhinorrhea (CSF)Cerebrospinal fluid rhinorrhea (CSF)
Cerebrospinal fluid rhinorrhea (CSF)
 
Robotic surgery in ENT
Robotic surgery in ENTRobotic surgery in ENT
Robotic surgery in ENT
 
Anatomy of Skullbase
Anatomy of SkullbaseAnatomy of Skullbase
Anatomy of Skullbase
 
Anatomy & physiology of thyroid gland
Anatomy & physiology of thyroid glandAnatomy & physiology of thyroid gland
Anatomy & physiology of thyroid gland
 
Narrow band imaging
Narrow  band imagingNarrow  band imaging
Narrow band imaging
 
Trauma to the face
Trauma to the faceTrauma to the face
Trauma to the face
 
Anatomy of larynx
Anatomy of larynxAnatomy of larynx
Anatomy of larynx
 
Anatomy of Lateral wall of nose
Anatomy of Lateral wall of noseAnatomy of Lateral wall of nose
Anatomy of Lateral wall of nose
 

Dernier

Neurological history taking (2024) .
Neurological  history  taking  (2024)  .Neurological  history  taking  (2024)  .
Neurological history taking (2024) .Mohamed Rizk Khodair
 
FDMA FLAP - The first dorsal metacarpal artery (FDMA) flap is used mainly for...
FDMA FLAP - The first dorsal metacarpal artery (FDMA) flap is used mainly for...FDMA FLAP - The first dorsal metacarpal artery (FDMA) flap is used mainly for...
FDMA FLAP - The first dorsal metacarpal artery (FDMA) flap is used mainly for...Shubhanshu Gaurav
 
Physiology of Smooth Muscles -Mechanics of contraction and relaxation
Physiology of Smooth Muscles -Mechanics of contraction and relaxationPhysiology of Smooth Muscles -Mechanics of contraction and relaxation
Physiology of Smooth Muscles -Mechanics of contraction and relaxationMedicoseAcademics
 
ANATOMICAL FAETURES OF BONES FOR NURSING STUDENTS .pptx
ANATOMICAL FAETURES OF BONES  FOR NURSING STUDENTS .pptxANATOMICAL FAETURES OF BONES  FOR NURSING STUDENTS .pptx
ANATOMICAL FAETURES OF BONES FOR NURSING STUDENTS .pptxWINCY THIRUMURUGAN
 
ayurvedic formulations herbal drug technologyppt
ayurvedic formulations herbal drug technologypptayurvedic formulations herbal drug technologyppt
ayurvedic formulations herbal drug technologypptPradnya Wadekar
 
Generative AI in Health Care a scoping review and a persoanl experience.
Generative AI in Health Care a scoping review and a persoanl experience.Generative AI in Health Care a scoping review and a persoanl experience.
Generative AI in Health Care a scoping review and a persoanl experience.Vaikunthan Rajaratnam
 
Unit I herbs as raw materials, biodynamic agriculture.ppt
Unit I herbs as raw materials, biodynamic agriculture.pptUnit I herbs as raw materials, biodynamic agriculture.ppt
Unit I herbs as raw materials, biodynamic agriculture.pptPradnya Wadekar
 
Different drug regularity bodies in different countries.
Different drug regularity bodies in different countries.Different drug regularity bodies in different countries.
Different drug regularity bodies in different countries.kishan singh tomar
 
Breast cancer -ONCO IN MEDICAL AND SURGICAL NURSING.pptx
Breast cancer -ONCO IN MEDICAL AND SURGICAL NURSING.pptxBreast cancer -ONCO IN MEDICAL AND SURGICAL NURSING.pptx
Breast cancer -ONCO IN MEDICAL AND SURGICAL NURSING.pptxNaveenkumar267201
 
Male Infertility, Antioxidants and Beyond
Male Infertility, Antioxidants and BeyondMale Infertility, Antioxidants and Beyond
Male Infertility, Antioxidants and BeyondSujoy Dasgupta
 
Female Reproductive Physiology Before Pregnancy
Female Reproductive Physiology Before PregnancyFemale Reproductive Physiology Before Pregnancy
Female Reproductive Physiology Before PregnancyMedicoseAcademics
 
"Radical excision of DIE in subferile women with deep infiltrating endometrio...
"Radical excision of DIE in subferile women with deep infiltrating endometrio..."Radical excision of DIE in subferile women with deep infiltrating endometrio...
"Radical excision of DIE in subferile women with deep infiltrating endometrio...Sujoy Dasgupta
 
Role of Soap based and synthetic or syndets bar
Role of  Soap based and synthetic or syndets barRole of  Soap based and synthetic or syndets bar
Role of Soap based and synthetic or syndets barmohitRahangdale
 
SGK RỐI LOẠN KALI MÁU CỰC KỲ QUAN TRỌNG.pdf
SGK RỐI LOẠN KALI MÁU CỰC KỲ QUAN TRỌNG.pdfSGK RỐI LOẠN KALI MÁU CỰC KỲ QUAN TRỌNG.pdf
SGK RỐI LOẠN KALI MÁU CỰC KỲ QUAN TRỌNG.pdfHongBiThi1
 
BENIGN BREAST DISEASE
BENIGN BREAST DISEASE BENIGN BREAST DISEASE
BENIGN BREAST DISEASE Mamatha Lakka
 
Clinical Research Informatics Year-in-Review 2024
Clinical Research Informatics Year-in-Review 2024Clinical Research Informatics Year-in-Review 2024
Clinical Research Informatics Year-in-Review 2024Peter Embi
 
Adenomyosis or Fibroid- making right diagnosis
Adenomyosis or Fibroid- making right diagnosisAdenomyosis or Fibroid- making right diagnosis
Adenomyosis or Fibroid- making right diagnosisSujoy Dasgupta
 

Dernier (20)

Neurological history taking (2024) .
Neurological  history  taking  (2024)  .Neurological  history  taking  (2024)  .
Neurological history taking (2024) .
 
FDMA FLAP - The first dorsal metacarpal artery (FDMA) flap is used mainly for...
FDMA FLAP - The first dorsal metacarpal artery (FDMA) flap is used mainly for...FDMA FLAP - The first dorsal metacarpal artery (FDMA) flap is used mainly for...
FDMA FLAP - The first dorsal metacarpal artery (FDMA) flap is used mainly for...
 
GOUT UPDATE AHMED YEHIA 2024, case based approach with application of the lat...
GOUT UPDATE AHMED YEHIA 2024, case based approach with application of the lat...GOUT UPDATE AHMED YEHIA 2024, case based approach with application of the lat...
GOUT UPDATE AHMED YEHIA 2024, case based approach with application of the lat...
 
Physiology of Smooth Muscles -Mechanics of contraction and relaxation
Physiology of Smooth Muscles -Mechanics of contraction and relaxationPhysiology of Smooth Muscles -Mechanics of contraction and relaxation
Physiology of Smooth Muscles -Mechanics of contraction and relaxation
 
American College of physicians ACP high value care recommendations in rheumat...
American College of physicians ACP high value care recommendations in rheumat...American College of physicians ACP high value care recommendations in rheumat...
American College of physicians ACP high value care recommendations in rheumat...
 
ANATOMICAL FAETURES OF BONES FOR NURSING STUDENTS .pptx
ANATOMICAL FAETURES OF BONES  FOR NURSING STUDENTS .pptxANATOMICAL FAETURES OF BONES  FOR NURSING STUDENTS .pptx
ANATOMICAL FAETURES OF BONES FOR NURSING STUDENTS .pptx
 
ayurvedic formulations herbal drug technologyppt
ayurvedic formulations herbal drug technologypptayurvedic formulations herbal drug technologyppt
ayurvedic formulations herbal drug technologyppt
 
Generative AI in Health Care a scoping review and a persoanl experience.
Generative AI in Health Care a scoping review and a persoanl experience.Generative AI in Health Care a scoping review and a persoanl experience.
Generative AI in Health Care a scoping review and a persoanl experience.
 
Unit I herbs as raw materials, biodynamic agriculture.ppt
Unit I herbs as raw materials, biodynamic agriculture.pptUnit I herbs as raw materials, biodynamic agriculture.ppt
Unit I herbs as raw materials, biodynamic agriculture.ppt
 
Different drug regularity bodies in different countries.
Different drug regularity bodies in different countries.Different drug regularity bodies in different countries.
Different drug regularity bodies in different countries.
 
Breast cancer -ONCO IN MEDICAL AND SURGICAL NURSING.pptx
Breast cancer -ONCO IN MEDICAL AND SURGICAL NURSING.pptxBreast cancer -ONCO IN MEDICAL AND SURGICAL NURSING.pptx
Breast cancer -ONCO IN MEDICAL AND SURGICAL NURSING.pptx
 
Male Infertility, Antioxidants and Beyond
Male Infertility, Antioxidants and BeyondMale Infertility, Antioxidants and Beyond
Male Infertility, Antioxidants and Beyond
 
Female Reproductive Physiology Before Pregnancy
Female Reproductive Physiology Before PregnancyFemale Reproductive Physiology Before Pregnancy
Female Reproductive Physiology Before Pregnancy
 
"Radical excision of DIE in subferile women with deep infiltrating endometrio...
"Radical excision of DIE in subferile women with deep infiltrating endometrio..."Radical excision of DIE in subferile women with deep infiltrating endometrio...
"Radical excision of DIE in subferile women with deep infiltrating endometrio...
 
Role of Soap based and synthetic or syndets bar
Role of  Soap based and synthetic or syndets barRole of  Soap based and synthetic or syndets bar
Role of Soap based and synthetic or syndets bar
 
SGK RỐI LOẠN KALI MÁU CỰC KỲ QUAN TRỌNG.pdf
SGK RỐI LOẠN KALI MÁU CỰC KỲ QUAN TRỌNG.pdfSGK RỐI LOẠN KALI MÁU CỰC KỲ QUAN TRỌNG.pdf
SGK RỐI LOẠN KALI MÁU CỰC KỲ QUAN TRỌNG.pdf
 
How to master Steroid (glucocorticoids) prescription, different scenarios, ca...
How to master Steroid (glucocorticoids) prescription, different scenarios, ca...How to master Steroid (glucocorticoids) prescription, different scenarios, ca...
How to master Steroid (glucocorticoids) prescription, different scenarios, ca...
 
BENIGN BREAST DISEASE
BENIGN BREAST DISEASE BENIGN BREAST DISEASE
BENIGN BREAST DISEASE
 
Clinical Research Informatics Year-in-Review 2024
Clinical Research Informatics Year-in-Review 2024Clinical Research Informatics Year-in-Review 2024
Clinical Research Informatics Year-in-Review 2024
 
Adenomyosis or Fibroid- making right diagnosis
Adenomyosis or Fibroid- making right diagnosisAdenomyosis or Fibroid- making right diagnosis
Adenomyosis or Fibroid- making right diagnosis
 

Physiology of olfaction

  • 1. Physiology of Olfaction Dr. Jinu V Iype 1st year Post Graduate Department of ENT
  • 3. INTRODUCTION • Senseof smell has been recently heavily studied because of it’s importance to human being’s survival. • It helps to track food , can alert us todanger like gasleak, fire, rotten food. • It is also linked to brain that process emotion and memory.
  • 4. Olfaction or Olfactory perception - the sense of smell mediated by a group of specialised sensory cells in nasal cavity. Odour -the property of a substance which gives it a particular smell.
  • 5. Anatomy of Olfactory Stimulation 1.Nasal Passageways
  • 6. • Olfactory nerve (cranial nerve I) stimulation, which is necessary for identification of most odorants, depends on the odorant molecules’ reaching the olfactory mucosa at the top of the nasal cavity.
  • 7. • Although molecules can reach the olfactory cleft by diffusion, essentially olfaction requires some type of nasal airflow. • During eating, there is a retro nasal flow of odorant molecules that stimulate the olfactory receptors at the top of the nose and contribute greatly to the flavor of the food.
  • 8. Swallowing and Deglutition Retronasal Airflow Production of flavour from swallowed food Adds Smell to Taste
  • 9. • At physiologic airflow rates, approximately 50% of the total airflow passes through the middle meatus, • ~ 35% flowing through the inferior meatus • About 15% flows through the olfactory region
  • 10. • Sniffing is an almost universally performed maneuver when a person is presented with an olfactory stimulus. • It increase the number of olfactory molecules in the olfactory cleft by means of a transient change in the airflow pattern of the nose. • A sniff also may allow the trigeminal nerve to alert the central olfactory neurons that an odorant is coming.
  • 12. • For molecules to reach the olfactory area, they must pass through the tall but narrow nasal passageways. • The epithelium lining the walls of these passageways is wet, has variable thickness.
  • 13. 2. Olfactory Mucus • After the odorant molecules reach the olfactory region, they must interact with the mucus overlying the receptor cells. • The mucus apparently comes from both Bowman’s glands deep in the lamina propria (only of serous type in humans) and the adjacent respiratory mucosa (goblet cells)
  • 14. • To reach the olfactory receptors, the odorant molecules must be soluble in the mucus. • Changes in the thickness or composition of the mucus can influence the diffusion time required for odorant molecules to reach the receptor sites
  • 15. • Once in the olfactory mucus-epithelial system, the rate at which the odorant is cleared also is important. • Studies shows that 79% of a radioactively labeled odorant (butanol) remained trapped in the mucus 30 minutes after inspiratory exposure, whereas radioactively labeled octane cleared rapidly.
  • 16. 3. Olfactory Epithelium • Located 7 cm inside the nasal cavity, the olfactory sensory neurons are protected in a 1- mm-wide crevice of the postero superior nose. • At the epithelial surface, these bipolar neurons are exposed to the outside world through their dendrites and cilia.
  • 17. • A number of research groups have shown that there is mixing of olfactory and respiratory epithelial tissues in adult. • The number of these clumps of respiratory epithelium, which are found in the olfactory area, increases with age, suggesting that a loss of primary olfactory neurons at least partially explains the decreased olfactory ability associated with aging.
  • 18. Low magnification of the surface of the nasal cavity taken from a transition region. Patches of respiratory (R) epithelium (dark areas) can be seen within the olfactory (O) region
  • 19. Low-power three-dimensional scanning view of the olfactory epithelium and lamina propria. The olfactory epithelium (E) overlies a thick connective tissue lamina propria that contains olfactory axon fascicles (A x) and blood vessels (V) (×248). • The human olfactory epithelium covers an area of roughly 1 cm2 on each side. • The epithelium is pseudostratified columnar, and it rests on a vascular lamina propria with no submucosa
  • 21. • This portion of mucosa can be readily identified from the rest of the nasal mucosa by its unique yellowish color.
  • 22. Embryologically • Olfactory receptors derive from neuroblasts. These neuroblasts differentiates to form olfactory placodes. • The central part of each placode invagiantes giving rise to olfactory sac. • Olfactory sac opens anteriorly
  • 23. • Olfactory organ is the only part of the body in which the cell bodies of neurons lie at the surface, directly in contact with the external environment.
  • 24. four main cell types 1. ciliated olfactory receptors 2. microvillar cells 3. supporting (sustentacular) cells 4.basal cells
  • 25. The olfactory receptor neuron • Bipolar • Club-shaped peripheral “knob” that bears the cilia. • Extends odourant receptor-containing cilia into mucus. • olfactory nerve 15 to 20 foramina in the cribriform plate to synapse in the bulb
  • 26. High-power magnification of an olfactory knob with long cilia gradually tapering as they extend over the epithelial surface. At the base of individual cilia, a necklace-like structure (arrow) can be seen on the surface of the olfactory knob
  • 27. • Allison et al estimate the rabbit to have approximately 50 million olfactory axons, whereas Jafek estimates humans to have only 6 million bilaterally.
  • 28. • The olfactory ensheathing cells are unique in that they share characteristics that are common with Schwann cells and central glial cells. • Because olfactory neurons - ability to regenerate and make functional synapses with the olfactory bulb. • possible therapeutic potential for repair of peripheral neuronal injury. • potential agents for reversing spinal cord injuries and demyelinating diseases.
  • 29. The microvillar cell • one tenth as often as the ciliated olfactory neurons. • flask-shaped, is located near the epithelial surface, and has an apical membrane containing microvilli that project into the mucus overlying the epithelium • The deep end of the cell tapers to a thin, axon- like cytoplasmic projection that proceeds into the lamina propria.
  • 30. • Low-power magnification of fractured olfactory epithelium illustrating the axon- like processes (arrows) from microvillar cells (M), which extend basally between supporting cells
  • 31. SUPPORTING CELLS/SUSTENTACULAR CELLS • Tall cells have an apical membrane that joins tightly with the surface of the receptor cells and the microvillar cells. • Do not generate action potentials, nor are they electrically coupled to each other
  • 32. • Play a role in ion and water regulation and, along with Bowman’s gland duct cells, contain xenobiotic enzymes such as cytochrome P-450 that likely contribute to odorant metabolism.
  • 33. Cross-sectional view of the olfactory epithelium showing the columnar supporting cells (S) that extend the full length of the epithelium. An olfactory neuron (O) with its dendrite and basal cell (B) can be seen among supporting cells
  • 34. BASAL CELLS • Sit along the basal lamina. • Two groups of replicating cells Horizontal basal cells Globose basal cells are just above positioned between the basal lamina the horizontal basal cells & immature neurons.
  • 35. •The globose basal cells seem to be responsible for the continuous replacement of olfactory receptor neurons
  • 36. • During severe insult →repopulate the nonneuronal components of the epithelium . • The replication cycle is between 3 and 7 weeks. • When the new receptor cell forms, it also projects its axon to the olfactory bulb, where it synapses with second-order neurons, thereby ensuring continual olfactory function and continual olfactory neuron replacement.
  • 37. Vomeronasal Organ • Many mammals have an identifiable pit or groove in the anteroinferior part of the nasal septum that contains chemosensitive cells. • In most of these animals, a nerve can be identified connecting these cells to the central nervous system, to an accessory olfactory bulb.
  • 38. • Biopsy studies of the nasal mucosa in the small pit often seen along the anteroinferior nasal septum (Jacobson’s organ) show olfactory-like histology but no central connection. • Electrical activity elicited by certain compounds directly delivered to the vomeronasal area has been shown to cause changes in blood pressure, heart rate, and hormonal levels.
  • 39. • It is believed to detect external chemical signals called pheromones. • These signals, which are not detected consciously as odors by the olfactory system, mediate human autonomic, psychological, and endocrineresponses.
  • 40. Olfactory Bulb • Located directly over the cribriform plate. • first relay station in the olfactory pathway where the primary olfactory neurons synapse with secondary neurons.
  • 41. Neural components are arranged in six concentric layers: the olfactory nerve  glomerular External plexiform  mitral cell  internal plexiform granule cell
  • 42. The receptor cell axons of the olfactory nerve layer →the glomeruli → synapse with the dendrites of the mitral and tufted cells within the spherical glomeruli.
  • 43. These second order cells, in turn, send collaterals that synapse within the periglomerular and external plexiform layers, resulting in “reverberating” circuits in which negative and positive feedback occur. mitral cells modulate their own output by activating granule cells (which are inhibitory to them).
  • 44. • The mitral and tufted cell axons project ipsilaterally to the primary olfactory cortex via the olfactory tract
  • 45. Olfactory tract enters brain 2 pathways Lateral Olfactory stria Medial Olfactory stria
  • 47. MEDIAL OLFACTORY AREA • consists of a group of nuclei • located in the mid basal portions of the brain immediately • Contain septal nuclei- feed into the hypothalamus and other primitive portions of the brain’s limbic system
  • 48. Composed of prepyriform pyriform cortex cortical portion of amygdaloid nuclei. signal pathways- almost all portions of limbic system , especially hippocampus- important for learning like or dislike for food stuffs.
  • 49. An important feature of the lateral olfactory area is that many signal pathways from this area also feed directly into an older part of the cerebral cortex called the paleocortex in the anteromedial portion of the temporal lobe. This is the only area of the entire cerebral cortex where sensory signals pass directly to the cortex without passing first through the thalamus.
  • 50. • The mitral and tufted cell axons project ipsilaterally to the primary olfactory cortex via the olfactory tract without an intervening thalamic synapse
  • 51. Primary olfactory cortex is comprised of the Anterior Olfactory Nucleus - Pyriform Cortex- Olfactory tubercle - Entorhinal area - Amygdaloid Cortex - Corticomedial nuclear group of amygdala.
  • 52. Anterior Olfactory Nucleus Coordination of inputs from contalateral olfactory cortex Transfer of Olfactory memories from one side to other Pyriform Cortex Olfactory discrimination Amygdala Emotional response to olfactory stimuli Entorhinal Cortex Olfactory Memories
  • 54. Olfactory pathway • First order neuron : olfactory Epithelium to glomerulus • Second order neuron :It is formed of the cells of the olfactory bulb (mitral cells & Tufted cell) Passes centrally as the olfactory tract . • Third order neuron: Pyriform Cortex(Area 28) contain primary olfactory cortex, which contain 3rd order neuron
  • 56. Very Old Olfactory System •More primitive responses to olfaction salivation, primitive emotional drives to smell Less Old Olfactory System • Learned control of food intake • Aversion to food that have caused nausea & vomiting Newer System • Odour discrimintation & analysis of odour
  • 57. Olfactory Transduction and Coding • Once the odorant molecule is dissolved in the olfactory mucus
  • 58. • Soluble binding proteins, like odorant-binding protein -> enhance the access of odorants to the olfactory receptors. • Same odorant-binding protein molecules act to remove odorant molecules from the region of the receptor cell after transduction.
  • 59. • The actual transformation of odorant chemical information into an electrical action potential occurs as a result of specific interactions between odorant molecules and receptor proteins on the surface of olfactory cilia. • With the binding of the receptor to an odorant, adenylate cyclase is activated by G protein– coupled receptors and converts adenosine triphosphate (ATP) into cyclic adenosine monophosphate( cAMP).
  • 60. • The cAMP then binds to a Na, Ca ion channel to allow influx of these ions. • As more channels open, the cell depolarizes, and an action potential is produced
  • 61. • Once the peripheral olfactory receptor cells are depolarized, there begins a convergence of electrical information toward the olfactory bulb → glomeruli and mitral / tufted cells of the olfactory bulb → Olfactory cortex
  • 62. Molecular structure – Moncrieff 1967 Electrochemical Reactions Stereospatial patterns Molecular Properties Olfactory mucus morphology
  • 63. MOLECULAR STRUCTURE • By Moncrieff 1967 • Suggested that molecular structure is important. • No stereospecific olfactory receptors have been demonstrated.
  • 64. Odour mol + Receptor  Photochemical reaction  SIGNALTRANSDUCTION Receptors containing carotenoids By Briggs and Duncan,1962
  • 65. By Mozell, 1970 Certain receptors could have a stereospatial, lock and key form, and receptor cells fire when the surface membrane is altered.
  • 67. By Laffort et al,1974 Molecular properties depends on -molecular volume at boiling point -proton affinity and donation, -local polarization within the molecule.
  • 68. Holley and Doving,1977 Nature of smell - Pattern of stimulus within mucosal configuration of receptor cells This theory is based on specific receptor sites & on their position within olfactory mucosa
  • 69.  Vibration Theory  Olfactory Pigment Theory  Enzyme Theory  Penetrating and Puncturing theory
  • 70. Randerbrock 1968 Olfactory perceptors are peptide chains vibrating in an alpha helix. Odourant molecules forms a band with peptide chain modulating the vibration-transmitted to nerves. Pigment Theory Rosenberg 1968 odourant molecule + olfactory pigment- increased electrical conductivity
  • 71. By Davies Odourant molecules penetrate membrane of olfactory receptor cell- diffuse-leaving a hole. Leakage of Sodium & pottasium occurs- nerve impulse
  • 74. TYPESOF OLFACTORY DYSFUNCTION o Anosmia-absenceof smell o Hyposmiamicrosmia- diminished olfactorysensitivity o Dysosmia-distorted senseof smell o Phantosmia- perception of anodorant when noneis presentl / Olfactory hallucination. o Agnosia-inability to classify,contrast, or identify odor sensationsverbally, eventhough the ability to distinguish between odorants maybenormal o Hyperosmia-Abnormally acute smell function (Rare condition )
  • 75. CLASSIFICATION& ETIOLOGY • TRANSPORT OLFACTORY LOSS Olfactory dysfunctions canbe causedby conditions that interfere with the accessof the odorant to the olfactory neuro-epithelium due to either swollen nasalmucous membrane, structural changesand/or mucussecretion. Causes-Allergy rhinitis, Bacterial rhinitis and sinusitis, Congenital abnormality like encephalocele, Deviated NasalSeptum, Nasal neoplasms, Nasalpolyps, Nasal surgery,Old age, Viral infections.
  • 76. • SENSORY OLFACTORY LOSS Olfactory dysfunctions can be caused by conditions that damage to the neuroepithelium. Causes-Drugs that affect cell turn over and inhalations of toxic chemicals, viral infections, neoplasms, radiation therapy.
  • 77. • NEURAL OLFACTORY LOSS • Olfactory dysfunctions canalso be causedby conditions that damagethe central olfactory pathways. • Causes-AIDS,Alzheimer’s disease,Alcoholism, Chemical Toxins,Cigarette smoke,Diabetes Mellitus, Depression, Drugs, Huntington’s chorea, Hypothyroidism, Kallmann syndrome, Korsakoff psychosis,Malnutrition, Neoplasm, Neurosurgery, Parkinson disease,Trauma,Vitamin B12def., Zinc deficiency
  • 78. APPROACHTO OLFACTORY DYSFUNCTION A.DETAILEDMEDICALHISTORY Onset, course, nature of impairment, their previous illness andthen medications taken. B. PHYSICALEXAMINATION Thorough ENT,head and neck examinations including nasal endoscopy. Aneurological examination emphasizing the cranial nerves, cerebellar and sensorimotor function is essential. Psychological examination like general mood and check for signsof depression should bedone.
  • 79. C.LABORATORYFINDINGS • Biopsy of olfactory neuroepithelium can be done in rarecases D.IMAGING • Coronal CTscanand MRI Brain are useful.
  • 80. sudden olfactory loss suggests the possibility of head trauma, infection, ischemia, or a psychogenic condition. Gradual loss the development of degenerative processes, progressive obstructive lesions or tumors within the olfactory receptor region or more central neural structures. Intermittent loss can be indicative of an intranasal inflammatory process.
  • 81. • A family history of smell dysfunction may suggest a genetic basis Kallmann’s syndrome : Delayed puberty in associationwith anosmia (with or without midline craniofacial abnormalities, deafness, and renal anomalies
  • 82. Quantitative Olfactory Testing (1)verify the validity of the patient’s complaint, (2)characterize the exact nature and degree of the problem, (3) accurately monitor changes in function over time (4) detect malingering, (5)obtain an objective basis for determining compensation for disability.
  • 83. UNIVERSITYOFPENNSYLVANIA SMELLIDENTIFICATIONTEST (UPSIT) • Most commonly used & most superiorand reliable test. • Self-administered in 10-15minutes • Scoredin <1 minute by non-med person • Available in variouslanguages • 40 “scratch & sniff “ patches • Pt. choosesfrom 4 answers& must choose1 • Candetect malingering • Dysfunction classified asNormosmia, anosmia, mild, moderate or severe microsmia, or probable malingering
  • 84. UPSIT
  • 85. To assess olfaction unilaterally, the naris contralateral to the tested side should be occluded without distorting the nasal valve region. This can be easily accomplished by sealing the contralateral naris using a piece of MicrofoamTM. The patient is instructed to sniff the stimulus normally and to exhale through the mouth. Such occlusion not only prevents air from entering the olfactory cleft from the contralateral naris
  • 86. Olfactory event-related potentials (OERPs) • synchronized brain electroencephalographic (EEG) activity induced by repeated pulsatile presentations of an odorant is isolated from overall EEG activity Used as :- sensitive and useful in detecting malingering
  • 87. ELECTRO-OLFACTOGRAM (EOG) • Detected via an electrode placed on the surface of the olfactory neuroepithelium
  • 88. DIFFERENTIALDIAGNOSIS • At present, no psychophysical methods to differentiate sensory from neural hearingloss. • History of olfactory lossgivesan important clues tothe cause. • Leadingcausesof olfactory dysfunctions are head trauma and viral infections. • Headtrauma are more common causeof anosmia in children and young adults whereas viral infectionsare more common causein older adults.
  • 89. • Congenital anosmia occurs in Kallmann syndrome and also in albinism. • Meningioma of inferior frontal region is the most common neoplastic causeof anosmia. • Dysomiais associatedwith depression.
  • 90. TREATMENT • Transport olfactory loss Thefollowing treatments are effective in restoring senseof smell: i. Allergy management ii. Antibiotic therapy iii. Topicaland systemic glucocorticoid therapy iv. Operations for nasalobstruction.
  • 91. • Sensorineural Olfactory loss. No treatment with demonstrated efficacyfor Sensorineural Olfactory loss. Fortunately, spontaneous recovery occurs. Someclinicians advocate zinc and vitamin therapy espVitaminA.