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Neurosciences 2.14 -- Gustatory and Olfactory Systems

Terms

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where are taste buds found?
most are found in papillae on the tongue

some are also found on the soft palate, epiglottis, and lower oral pharynx
what are the three cell types within the taste buds?
(1) basal cells

(2) supporting cells

(3) sensory cells
taste: basal cells
undifferentiated stem cells located near the base of the taste bud; undergo a process of continuous regeneration --> replace sensory or supporting cells
do supporting cells respond to taste stimuli?
no
taste receptor cells
- aka
- general definition
aka sensory cells

covered with microvilli, provide ideal sites for the transduction of chemical stimuli into electrical currents
what are the four types of papillae?
(1) filiform

(2) fungiform

(3) foliate

(4) circumvallate
fungiform papillae
scattered across dorsal surface of tongue, most numerous near the anterior tip; contain 3-5 taste buds which are located on the dorsal surface
foliate papillae
located on the lateral border of the tongue; taste buds are in folds on the sides of the papillae
circumvallate papillae
largest of all papillae, located in rows near base of tongue; surrounded by a trench containing _numerous_ taste buds
filiform papillae
most abundant type of papillae found on tongue; but do NOT contain taste buds
which three CNs are involved in the taste pathway?
(1) facial

(2) glossopharyngeal

(3) vagus
CN VII
- innervates?
- cell bodies where?
subserves taste over the anterior 2/3 of the tongue

cell bodies in the geniculate ganglion
CN IX
- innervates?
- cell bodies where?
innervates the posterior 1/3 of the tongue

cell bodies originating in the petrosal ganglion
CN X
- innervates?
- cell bodies wher?
innervates epiglottis and lower pharynx

cell bodies originating in the nodose ganglion
CN V
- involved in taste?
- innervates?
- cell bodies where?
not involved in taste

innervates anterior 2/3 tongue: touch, temp, pain

gasserian ganglion
cortical taste area
region of the neocortex including the lateral portion of the postcentral gyrus and the opercular insular cortex
what are the four basic taste sensations?
salty, sweet, sour, and bitter
salty sensations mediated by?
direct interaction with ion channel
sour sensations mediated by?
direct action -- closure of K+ channels
bitter sensations mediated by?
IP3 / Ca2+ 2nd messengers
sweet sensations mediated by?
cAMP 2nd messenger
sensitivity distribution
bitter is best in posterior, sour is good along sides of tongue (both IX)

salty and sweet are good on ant 2/3 (VII)
hypogeusia
dec in taste sensitivity
ageusia
absence of the sense of taste
hypergeusia
an inc in taste sensitivity
dysgeusia
impairment or distortion of taste
cacogeusia
a bad or foul sense of taste
parageusia
a taste sensation in the absence of the appropriate stimuli
what three basic cell types make up the olfactory epithelium?
(1) Basal Cells

(2) Supporting Cells

(3) Olfactory Receptor Cells
what are the two differences between neurogenesis of olfactory receptor cells and development of gustatory epithelium?
olfactory takes longer (25-30 vs. 10 days)

olfactory receptor cells are true nerve cells
olfactory: basal cells
undifferentiated stem cells which give rise to olfactory receptor cells (every 25-30 days)
olfactory: supporting cells
columnar epithelial cells; contain numerous microvilli which extend into the olfactory mucosa and contain secretory granules
olfactory: receptor cells
large cell body, rod, olfactory knob

olfactory vesicle (knob) contains cilia which extend out, may be the site for transduction of odor molecules
olfactory nerve fibers are unique for which two reasons?
(1) very small fibers -- very slow

(2) within a single Schwann cell invagination, these unmyelinated fibers run together in bundles and apparently are not insulated from one another
besides the olfactory nerve, what other nerve innervates the epithelium? explain what it does?
trigeminal nerve detects noxious and caustic chemicals such as ammonia, formaldehyde, and other stinging and sometimes painful odors

this is NOT olfaction!
what are the layers of the olfactory bulb?
the glomerular layer, the outer plexiform layer, the mitral cell body layer, the inner plexiform layer, and the granule cell layer
what is the most important cell type in the olfactory bulb?
mitral cell
what do the mitral cells do?
they have dendrites which receive direct synaptic input from the olfactory nerve fibers; axons join together to form the olfactory tract
glomeruli
clusters of synaptic connections (first order olfactory nerve fibers & dendrites of 2nd order mitral cells)
periglomerular (PG) cells
inhibitory interneurons, provide for lateral inhibition of neighboring glomeruli
two fxns of dendrodendritic connxns in the olfactory bulb?
self-inhibition and lateral inhibition
hyposmia
a dec in smell sensitivity
anosmia
absence of sense of smell
hyperosmia
inc in smell sensitivity
dysosmia
impairment or distortion of the sense of smell
cacosmia
a bad or foul sense of smell
parosmia
a smell sensation in the absence of the appropriate odor stimulus

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