Chapter 15 - The Chemical Senses Flashcards
Three sensory systems are associated with the nose and mouth. Name them.
- The olfactory system
- The gustatory system
- The trigeminal chemosensory system
The …… system detects airborne molecules called odorants.
Olfactory
The ……… system detects ingested tastants (primarily water- or fat-soluble molecules)
Gustatory
The …… system provides information about irritating or noxious molecules that come into contact with the skin or the mucous membranes of the eye, nose and mouth.
Trigeminal chemosensory
Airborne molecules detected by the olfactory system is called..
Odorants
Where is the olfactory epithelium?
It lines the interior of the nose, at the roof of the nasal cavity.
Receptor cells for odourants have axons that project directly to …
The olfactory bulb.
The olfactory bulb has neurons that are innervated by the receptor cell axons of the olfactory epithelium. The olfactory bulb has axons that project to ..
- The pyriform cortex in the temporal lobe.
2. Other structures in the forebrain.
Which sensory system does not include a thalamic relay?
The olfactory system!
The pyriform cortex has one defining cytoarchitectonic feature. Which?
It has three layers, not six - therefor not defined as neocortex.
The olfactory system is the only sensory system that does not have a thalamic relay. The thalamus is still involved though.. how?
Although the initial pathway to the pyriform cortex bypass the thalamus, the thalamus does play an important role in subsequent stages of olfaction.
“In humans, olfaction is often considered the least acute of the senses”. You’ve heard this many times. Why do we think so?
It mainly relies on the finding that the surface area of our olfactory epithelium is vastly smaller in contrast with other mammals. A rat has a bigger olfactory epithelium than humans do.
One of the most consistent aspects of human olfactory perception is the …
The classification of odors as either pleasant and attractive or unpleasant and repulsive.
Clinicians use uniquely scented “probes” - such as coffee grounds or soap - to test the function of the olfactory nerve (cranial nerve I) as a part of the standard cranial nerve examination. Some individuals consistently fail to identify one or more common odors. Such chemosensory deficits are known as …
anosmias
What is an interesting feature of anosmia?
It is often restricted to a single odourant, suggesting that a specific element in the olfactory system - either an olfactory receptor gene or genes that control expression or function of specific odourant receptor genes - is inactivated.
Olfactory deficits are known to occur during a broad range of disorders. The cause of this is not known. Mention four disorders in which olfactory deficits are common.
- Eating disorders
- Diabetes
- Parkinson’s
- Schizophrenia
What are pheromones?
Specific odorants that play an important role in behaviour. Especially social, reproductive and parenting-behaviours.
In other animals, including many mammal species, pheromones are detected by a part of the olfactory epithelium called …
the vomeronasal organs.
Do humans have vomeronasal organs?
Primates, including humans, do not have vomeronasal organs, distinct vomeronasal receptors, or significant numbers of functional vomeronasal receptor genes.
So primates don’t have vomeronasal organs. Are there pheromones in the human species?
Despite many attempts to identify pheromones that elicit responses from humans, there is little evidence for them.
The neural portion of the olfactory epithelium includes several cell types. Name four types.
- Olfactory receptor neurons (ORNs)
- Bowman’s glands
- Basal cells
- Sustentacular (supporting) cells.
Give a short description of what the olfactory receptor neurons (ORNs) do.
They are the receptor cells that transmits chemical information to central locations. They have olfactory cilia that extend into a thick layer of mucus.
Give a short description of what the Bowman’s glands are.
Bowman’s glands are secretory specialisations that produce the mucus in the olfactory epithelium.
Research on the olfactory epithelium is possibly highly relevant for knowledge about more than just olfaction. Why?
Olfactory receptor neuron regeneration relies on maintaining a population of neural stem cells that give rise to new receptor neurons. This naturally occurring regeneration provides an opportunity to investigate how neural stem cells can successfully produce new neurons and reconstitute synaptic connections and function in the mature central nervous system.