Unit 2: Olfactory System Flashcards
The sense of olfaction is also called the ______ sense
osmatic
Components of the Olfactory System:
- olfactory mucosa
- olfactory nerves
- olfactory bulbs
- olfactory tracts
- olfactory cortex
Humans are considered _______ because our sense of smell is less important than sensations of vision or audition.
Microsmatic
Where is olfactory mucosa located?
located in superior aspect of each nasal fossa (sphenoethmoid recess) and extends onto the median nasal septum and lateral wall
What epithelial type is found in the olfactory mucosa?
Pseudostratified columnar epithelium
What kind of glands are found beneath epithelium and secrete fluid onto surface of mucosa to dissolve odorant
chemicals?
olfactory glands = Bowman’s glands
What are olfactory cells?
bipolar neurons that are modified to serve as olfactory receptor cells and conduct impulses
Olfactory cells have a limited functional life. What is this called and how long is it?
Olfactory cell turnover every 3 months or so
Describe the axons of olfactory cells?
axons are unmyelinated and form filaments of CN I
Specialized “dendrites” from olfactory cells on the mucosal surface and includes _______ receptors
odorant
bundles of axons (filaments of CN I) enter the cranial cavity through the ________ of the ethmoid bone
- foramina of the cribriform plate
What are glomeruli?
clusters of synaptic endings where axons (filaments of CN I) entering the olfactory bulb terminate
The end portion of an extension of the brain that is along the ventral
surface of the frontal lobe and associated with the olfactory system.
olfactory bulbs
What helps increase olfactory sensitivity?
Convergence where one mitral cell communicates with several olfactory cells
Dendrites of ________ arborize within the glomeruli with olfactory cell axons
principal neuron = mitral cell
Another type of neuron found within the olfactory bulbs? The axons of these cells travel through the olfactory tracts.
tufted cells
What comprises most of the fibers of the olfactory tract and project centrally in the brain?
mitral cell axons
association neurons of the olfactory bulb include:
periglomerular cells, granule cells and others
association neurons of the olfactory bulb serve to:
modify olfactory information before reaching the cerebral olfactory areas
most fibers of the olfactory tract are from ______, some from ________.
mitral cells, tufted cells
Fibers of the olfactory tract lead to the ________ at base of brain, which splits into a lateral and medial.
- olfactory trigone
- olfactory stria
Which stria of the olfactory tract do most of the fibers traverse?
lateral olfactory stria
Where do the fibers of that traverse the lateral olfactory stria travel to?
lateral olfactory area of the cerebrum
Some fibers of the olfactory tract make up an intermediate olfactory stria and terminate where?
in the anterior perforated substance
although often observed as a ridge of tissue, what does not include olfactory tract fibers to the septal area as originally thought?
the “medial olfactory stria”
What cerebral olfactory area receives input from the olfactory bulbs through fibers of the lateral olfactory stria?
Lateral Olfactory Area
Areas of the Lateral Olfactory Area includes:
(1) uncus (anterior part of the parahippocampal gyrus)
(2) limen insula (cortex of the ventral part of insula)
(3) part of the amygdala
The areas of the lateral olfactory area comprise the ____________, which is largely in the temporal bone.
Primary Olfactory Area
What is the Primary Olfactory Area responsible for?
responsible for subjective appreciation (awareness)
of an olfactory stimulus
Where is the olfactory association area located?
cortical areas adjacent to the primary olfactory cortex:
• lateral portion of the orbital surface of the frontal lobe
Note: permits the identification of the qualities of odors and also
the significance
The hippocampus and amygdala are part of the limbic system. What areas of the olfactory system are also part of it?
Lateral olfactory areas
How do the circuits of the limbic system allow odor to affect us?
odors to influence
memories, emotions, and visceral responses
What receives olfactory input from intermediate olfactory stria?
Anterior Perforated Substance
Where is the Anterior Perforated Substance
postitioned?
between the lateral and ‘medial’ olfactory stria
What area forms the intermediate olfactory area: plays no role in conscious olfaction
Anterior perforated substance
Neurons in the Anterior Perforated Substance play no role in conscious olfaction but instead mostly connect to structures in which system? It therefore appears to be involved in odors influencing what?
- Important structures of the limbic system
- memories, emotions, and visceral function
connections to the septal area and the hypothalamus permit olfactory sensations to influence _________.
autonomic activity (GI motility, salivation, or vomiting)
structures and pathways of the lateral and intermediate olfactory
areas, directly and indirectly, connect to what 3 areas?
- cerebral cortex
- limbic structures
- reticular system.
protocols to test olfactory sensations should consider the following:
a. each nostril should be tested separately
b. the substance should have an odor recognizable to the subject
c. substance should be volatile (aromatic): so that it can reach olfactory mucosa
d. substance must be non-irritative so you are not inadvertently testing nociception
Why do individuals who lose sensibility of smell often complain that food “doesn’t taste right” or “tastes bland”?
it is difficult to distinguish between qualities of smell and of taste
What is anosmia?
loss of smell
What are some destructive lesions that cause interruption of the pathway?
a. fractures of the ethmoid bone: leading to damage of CN I
b. meningioma in the floor of the anterior cranial fossa: which can interrupt an olfactory bulb or tract
What causes olfactory hallucinations?
irritative lesions of the lateral olfactory cortex
What are features of olfactory hallucinations?
a. inappropriate olfactory sensations
b. often unfamiliar to patient
c. usually extremely disagreeable
specific condition that affects the lateral olfactory area where patients experience disagreeable olfactory hallucinations and sometimes display convulsive, involuntary movements of the tongue and lips?
uncinate seizures
uncinate seizures are often associated with problems of what lobe?
Temporal
Following an uncinate seizure, patients experience a period of _______.
Confusion
