Olfactory System Flashcards
What is olfaction also called?
Osmatic sense
What are the components of the olfactory system?
Olfactory mucosa Olfactory nerve Olfactory bulbs Olfactory tracts Olfactory Cortex
Where is the olfactory mucosa located?
Located in superior aspect of feach nasal fossa (sphenoethmoid recess)
What areas of the nasal cavity are included in the olfactory mucosa?
Median nasal septum and lateral wall
What epithelia type is found in olfactory mucosa?
Pseudostratified Ciliated Columnar
What are olfactory glands also known as?
glands of Bowmen’s
What do Glands of Bowmen’s do?
Secretes mucous secretion that covers the olfactory mucosa
What are olfactory cells?
bipolar neurons that are modified to serve as the olfactory receptor
What is the length of time for olfactory cell turnover?
Active/functional life 2-4 months
What are the morphological features of olfactory cells?
Single dendrite that are arborized (branched) branches include odorant receptors in the plasma membrane
Are olfactory cells myelinated?
No they are unmyelinated and become the olfactory nerve
What forms olfactory nerves?
formed by axons of the olfactory cells
What do the axons have to travel through to enter the anterior cranial fossa?
Bundles of axons enter the cranial cavity through the cribiform foramina of the ethmoid bone
Where do the axons that enter the olfactory bulb terminate?
In clusters of endings called glomeruli
What are olfactory bulbs?
Extension of the brain that is along the ventral surface of the frontal lobe
What is the principal neuron of olfaction?
Mitral cells
What is the morphology of mitral cells?
Dendrites that arborize within the glomeruli and associate with olfactory cell axons
DO mitral cells communicate with more than one olfactory cell?
Yes, one mitral cell communicates with several olfactory cells (convergence helps increase olfactory sensitivity to low odor concentrations)
What cell axons comprise most of the fibers of the olfactory tract and where do they project?
Mitral cells comprise most of the fibers of the olfactory tract and project centrally in the brain to the olfactory cortex
What are tufted cells?
Another neuron in olfactory bulbs
What is the function of tufted cells?
Innervate glomeruli and send some axons through the olfactory tract
What cells make up the olfactory tract?
Most fibers are from mitral cells but some are from tufted cells
Where does the olfactory tract lead to?
Olfactory trigone at the base of the brain
What does the olfactory trigone do?
Appears to split into a lateral olfactory stria and medial olfactory stria
Where do most fibers that traverse the lateral olfactory stria go to?
The lateral olfactory area of the cerebrum
Where do the fibers that make up the intermediate olfactory stria terminate?
Anterior perforated substance
Does the medial olfactory strai include olfactory tract fibers?
No, medial olfactory stria does not include olfactory tract fibers to the septal area as originally thought
What does the lateral olfactory area do?
Receives input from the olfactory bulbs through fibers of the lateral olfactory stria
What does the lateral olfactory area contain?
Uncus
Limen Insula
Part of the amygdala
What is the uncus?
Anterior part of the parahippocompal gyrus
What is the limen insula?
Cortex of the ventral inferior part of the insula
What does the uncus, limen insula and part of the amygdala make?
Primary Olfactory area
Where is the primary olfactory area found?
Largely in the temporal lobe
What is the primary olfactory area responsible for?
Subjective appreciation of an olfactory stimulus (experience of a smell stimulus)
What is the olfactory association area?
Cortical areas adjacent to the primary olfacty cortex
What does the olfactory association area do?
Permits appreciation of significance of and identify different odors
What do the lateral olfactory areas together with hippocampus do?
Serve as important limbic system structures
Therefore this allows odors to influence our emotion, memories and viseral activities
Where is the anterior perforated substance found?
positioned between the lateral and medial olfactory stria
What does the anterior perforated substance form?
Intermediate olfactory area which plays a role in conscious olfaction
What do the anterior perforated substance do?
These neurons mostly connect to important structures and it is involved in emotional and autonomic responses to odor stimuli
How do you test the integrity of the olfactory pathway?
Often difficult to distinguish between qualities of smell and taste therefore those who lose smell can’t complain that food doesn’t taste right
What protocols should be followed to test olfactory sensations?
Each nostril should be tested separately
Substance should have an odor that’s recognizable
Substance should be volatile (aromatic)
Substance must be non-irrative or else pain stimulus occurs
What is anosmia?
Loss of smell
What can interrupt the olfactory pathway?
Nasal congestion
Fractures of the ethmoid bone
meningioma in the floor of the anterior cranial fossa
How do fractures of the ethmoid bone interrupt olfactory pathways?
It disrupts the olfactory nerve
How do meningiomas on the floor of the anterior cranial fossa interrupt olfactory pathways?
They disrupt the olfactory bulb or tract
What are olfactory hallucinations?
Inappropriate sensation of olfaction that are almost always unfamiliar and unpleasant
What irritative lesion of the lateral olfactory cortex can cause olfactory hallucination?
Uncinate seizures
What occurs with uncinate seizures?
Olfactory hallucinations
Convulsive involuntary movements of the lips and tongue
Mental confusion right after
What lobe is the seizure activity occuring for uncinate seizures?
In the temporal lobe (uncus)
