L12 & L13 - Nose 2/3

Question 1

Olfactory epithelium

Answer 1

Covers an area of 2.5cm2
* Location?
* Pseudostratified columnar
epithelium
* 3 cell types
– Olfactory cells
– Sustentacular cells (glial cells)
– Basal cells (stem cells)
* Bowmans glands – secrete a
mucous fluid
– Lubricates olfactory epithelium
– Dissolve oderant-containing gases
– Aid binding of oderant to receptors

Question 2

Olfactory nerve

Answer 2

Olfactory cells are bipolar neurons
axon
Dendrite expanded to form olfactory vesicle. Possesses long cilia
which contain receptors. Extends to epithelial surface.
Axons packaged into approximately 20 bundles on each side of nose -
the olfactory nerve, which passes through cribriform plate of ethmoid

Question 3

Smell detection

Answer 3

Odorants enter nasal cavity as a gas or
aerosol
1. Dissolve in the mucous and bind
to glycoproteins.
2. Presented to receptor proteins on
cilia – approx 3000 different
receptor proteins.
3. Stimulates depolarisation of
olfactory neurone
4. Olfactory neurone terminates in
the olfactory bulb
5. Spatial mapping of olfactory bulb -
specific sites of termination for
neurones that possess particular
chemical receptors

Adaptation - continuous stimuli becomes unnoticed

Question 4

Olfactory cell replacements

Answer 4

Olfactory cells are destroyed by wear and tear and lost by
desquamation. They are replaced approximately every 3 months

Question 5

Olfactory bulb

Answer 5

Located on the orbital surface of the frontal lobe
Site of convergence of olfactory nerves with 2nd order
neurones (tufted and mitral cells)

1. Nerve fibre layer: contains axons of
   primary olfactory neurones
2. Glomerular layer: contains approx 8000
   glomeruli where olfactory axons terminate
   on the dendrites of tufted and mitral cells
3. External plexiform layer: contains
   nerve cell bodies of tufted cells
4. Mitral cell layer: contains nerve
   cell bodies of mitral cells
5. Granule layer: axons of tufted and mitral
   cells and inhibitory interneurons

Question 6

Olfactory tract

Answer 6

The tract runs posteriorly to the
trigone where it divides into the
medial and lateral olfactory stria

Contains the axons of the mitral
and tufted cells and fibres from the
contralateral olfactory bulb

The anterior
olfactory nucleus
is located along
its length

Question 7

Anterior olfactory nucleus

Answer 7

Three small groups of nuclei
located along the olfactory tract
* Receive collateral branches of
tufted and mitral cells
* 3
rd order neurones arising here
pass through anterior
commissure to contralateral
olfactory bulb
* May be involved in setting
sensitivity to different odours

Question 8

Medial olfactory stria

Answer 8

Fibres in medial stria enter
anterior commissure
* Project to contralateral
olfactory bulb
* May have an inhibitory
action on the contralateral
olfactory bulb
* Enhances the more active
bulb thereby providing
directional cues to the
source of the olfactory
stimulus

Question 9

Lateral olfactory stria

Answer 9

Most of the axons of
tufted and mitral cells
pass in the lateral
olfactory stria to the
primary olfactory
areas

Question 10

Primary olfactory area

Answer 10

Pyriform area

Responsible for conscious awareness of olfactory stimuli
uncus
Projections sent to the olfactory association area
Includes those areas that receive afferent fibres from the olfactory
bulb; uncus , entorhinal area, limen insula* and amygdyloid body

Question 11

Olfactory association cortex

Answer 11

Monitors and interprets information from the primary olfactory cortex
may also include the lateral part of
the orbital surface of the frontal
lobe
Located in the entorhinal area

Question 12

Other olfactory cortical projections

Answer 12

Autonomic nervous system
via hypothalamus
Superior and inferior salivatory nuclei →
saliva production
Dorsal vagal nucleus → increased
peristalsis
hypothalamus
Brain stem
nuclei

Limbic system
Involved in retention and recall of
olfactory stimul

Question 13

Nose 3 - case study

Answer 13

if you can be bothered to do so