Gustatory And Olfactory Flashcards
How is it activated (what are the gustatory receptors) and how does a taste trigger a nerve impulse?
Gustatory Receptors= Taste buds (microvilli taste hairs extending from gustatory pore)
Base of each taste bud is penetrated by nerve fibers
Tastants interact with receptors via microvilli, depolarization of base, form synaptic contacts with gustatory afferents, action potential propagates.
What are the first order neurons (the cranial nerves) involved in taste?
Facial Nerve (7): anterior 2/3 of the tongue
Glossopharyngeal (9): posterior 1/3 of the tongue
Vagus Nerve (10): epiglottis and palatial taste buds
What is the pathway to the cortex?
Second order neuron: ascend in central tegmental tract to thalamus
Third order neuron: fibers travel in gustatory fibers through internal capsule, primary gustatory cortex (between inculcate and frontal operculum), secondary gustatory cortex (taste discrimination), also to amygdala (behavior to taste)
Which cranial nerves are associated with taste and under what circumstance might you evaluate taste clinically?
7 (9 is posterior tongue)
Tested with facial palsy (sprinkle salt on anterior tongue)
Where are the olfactory receptors?
Located in olfactory mucosa
Extended olfactory cilia
How does an odorant become a nerve impulse?
Odorants dissolve in mucus to stimulate receptors in cilia
Depolarization of primary olfactory neuron by activation of cyclic nucleotide pathway to produce action potential
How do the olfactory “nerves” gain access to the cranial cavity?
Central branches of bipolar olfactory neurons form axons of olfactory nerves (CN1)
Olfactory nerves are unmyelinated, travers the cribiform plate
Olfactory nerves terminate in olfactory bulb in floor of anterior cranial fossa above cribiform plate
What is the remainder of the pathway and where does it project?
Mitral cell axons form olfactory tract
Projection is DIRECTLY to the olfactory cortex (no thalamus)
How is the olfactory system connected with the ANS?
Amygdaloid nucleus sends axons to medial dorsal nucleus of thalamus
Axons then go to orbitofrontal cortex (association area)
Then sent to hypothalamus for mediation of behavioral and autonomic responses
What are some important clinical correlates to olfaction and how would they influence your decision on whether to test olfaction as part of a neurological examination?
Blocked nasal passages, infections, head trauma, frontal lobe tumors, dementia
Foster Kennedy syndrome.
Optic atrophy in one eye from frontal lobe tumor compressing the optic nerve
Papilledema in the other eye from the tumor causing increased intracranial pressure
How does dementia cause anosomia?
Neurodegeneration in olfactory bulbs, tracts and brain regions
Difficulty storing and retrieving memories of smell (entorrhinal cortex, hippocampus)
Cholinergic deficits due to damage
