olfactory

1. Olfactory NerveOlfactory Nerve
Dr Arun OommenDr Arun Oommen

2. • Anatomy and physiology

3. The olfactory nerve is a sensory nerve
with only one function- smell
First order neurons of olfactory
system are bipolar sensory cells
The olfactory receptors are located in
the superior posterior nasal septum and
lateral wall of the nasal cavity

4. Olfactory receptors have the unique
property to regenerate
Specific odorants stimulate specific
receptor cells and specific cells respond
to particular odorants
Around 20 central processes are given
off from these ciliated cells (filaments
of the 1st
nerve)

6. These filaments (olfactory nerve)
penetrate the cribriform plate of
ethmoid to enter the olfactory bulb.
They acquire a sheath of myelin
.
 In the bulb the olfactory afferent
fiber synapse with the dendrites of the
2nd
order neurons called the mitral and
tufted cells
At the point of synapse conglomerate of
fibres called the olfactory glomeruli are
formed

8. • The axons of the mitral and tufted cells
leave the bulb and course posteriorly as
the olfactory tract in the olfactory
sulcus on the orbital surface of the
frontal lobe
• The olfactory tract divide into medial
and lateral olfactory stria on either side
of the anterior perforating substance

10.  Some of these fibres decussate in the anterior
commissure and join fibres from the opposite olfactory
pathway. Some go to the olfactory trigone and
tuberculum olfactorium (In the APS)

11. Some of the medial olfactory stria
terminate in paraolfactory area, inf part
of cingulate gyrus, subcallosal gyrus

12. Other fibres esp the lateral stria
supply the ipsilateral piriform lobe of
the temporal cortex (primary
olfactory cortex) and terminate in the
• uncus,
• anterior hippocampal gyrus,
• pyriform cortex,
• entorhinal cortex,
• amygdaloid nucleus,

18. • The parahippocampal gyrus sent impulse
to the hippocampus
• The amygdaloid and hippocampal nuclei
(connected on each side thru the ant
commissure) sent projecting fibres to
the ant hypothalamic nuclei, mamillary
body ,tuber cinerum and habenular
nucleus

19. • This in turn project to the thalamus,
cingulate gyrus,striatum and
mesencephalic reticular formation]
• Olfaction is the only sensation not
directly processed in the thalamus
• Connection with the superior and
inferior salivatory nucleus is important
in reflex salivation

23. Clinical examination

24. 2 types of deficits
 Conductive deficits
 Sensorineural/Neurogenic

25. • Proper history
Past head injury
Smoking
Recent UTI
• Systemic illness
• Toxins medications and illicit drugs

26. Pre requisites
 Ensure nasal cavity is open
 Avoid irritating substances
 Test 1 nostril at a time

27. Substances used
 Cloves, Coffee ,Cinnamon
 Commercially available
substance like UPSIT (University of
Pennsylvania smell identification test)

28.  Unilateral loss of smell is more
significant than bilateral
 Perception of odor is more
important than accurate
identification
 Perceiving the presence of an odor
indicate continuity of the olfactory
pathway
Key points

29. 
 Identification of odor indicate intact
cortical function
 Since there is bilateral innervations,
lesion central to decussation does not
cause loss of smell and lesion in olfactory
cortex does not produce anosmia
 The appreciation of presence of smell
even without recognition excludes anosmia

30. Dissorders of olfactory function andDissorders of olfactory function and
localisationlocalisation

31. Terminologies
• Anosmia -Decreased sense of smell
• Hyperosmia -Increased sense of smell
• Dysosmia -Defective sense of smell
• Parosmia -Pervertion of smell
• Phantosmia -Perception of smell that
is no real
• Presbyosmia -Decresed smell due to
aging
• Cacosmia -Inappropriately
disagreeable odor
• Coprosmia -Faecal scent
• Olfactory agnosia - Inability to identify
detected odors

32.  Conditions causing disturbed olfactionConditions causing disturbed olfaction

33.  Congenital-Cleft palate, Downs syn, Turners, Kallmans , Familial
dysautonomia
 Endocrine/metabolic -adrenal insufficiency ,Diabetes, Hypothyroidism
 Iatrogenic-Ethmoidectomy, Hypertelorism, orbitofrontal lobectomy,
Radiotherapy, Rhinoplasty, temporal lobectomy, Repair of ACA anuerysm
 Infections-HIV, Herpes simplex, UTI
 Liver diseases -Cirrhosis, hepatitis
 Local processes -Hansens disease ,Polyps, Rhinitis, Adenoids, tumors
 Neurogenic-Alzheimers disease, Head trauma, Huntingtons disease
Migraines, meningiomas,(Foster kennedy syndrome) ,parkinsonism,
temporal lobe disease
 Psychiatric-Schizophrenia, Hypochondriasis
 Uremia
 Miscellaneous-Cystic fibrosis ,sarcoidosis ,Occupational exposure
,Refsums disease

34. Most common causes of anosmia
• Upper resp tract infection
• Head injury (15-30%)
1. Local injury to olfactory nerves at
cribriform plate due to coup or contrecoup
forces
2.Temporal/orbito frontal injury
• Nasal and sinus disease
• Idiopathic

35. • Lesions involving the orbital surface of
brain may cause unilateral anosmia
• In meningiomas of olfactory groove or
cribriform plate areas unilateral anosmias
occur followed by bilateral anosmias
• Parosmias and cacosmias are often due
to Psychiatric diseases or may follow head
injuries

36. • Olfactory hallucinations are often due to
Psychosis but can result from neoplastic
or vascular lesions of the central olfactory
system or following seizures
• In seizure focus involving medial temporal
lobe structures (uncinate or complex
partial seizures) often preceded by
disagreeable olfactory aura

37. • Following temporal lobectomy olfactory
discrimination is confined to ipsilateral
nostrils.
• Following right fronto orbital lobectomy
impairment seen in both nostrils
• In olfactory epileptic auras tumors are the
most common cause of seizures and the
amygdyla is the most likely symptomatic
zone

38. Foster kennedy
syndrome
 Seen in olfactory groove or
sphenoidal ridge meningiomas
or frontal lobe ICSOL
 3 signs-Ipsilateral anosmia
-Ipsilateral optic atrophy
-Contralateral papilledema

39. Pseudo Foster Kennedy
syndrome
 Seen when increased IC pressure of
any cause occur in patients who
have previous unilateral optic
atrophy
 Most commonly seen due to
sequential anterior ischaemic optic
neuropathy or optic neuritis (optic
disc oedema on one side associated
with optic disc atrophy on other
side)

40. Kallmann’s syndrome
 X linked dissorder
 Familial syndrome of permanent
anosmia with hypogonadotropic
hypogonadism.
 Hypoplasia or aplasia of olfactory
bulbs and tract
 Can be associated with cerebellar
ataxia and mirror movements of hands