Neuroanatomy of Taste and Olfaction Flashcards
What are the 5 basic tastes?
sweet
salty
sour
bitter
umami - ID of amino acids
Where does the olfactory bulb lie?
on the cribiform plate of the ethmoid bone
Where are olfactory receptor cells located?
in the roof of nasal cavity and on inferior surface of cribriform plate
along nasal septum and medial wall of superior turbinate
What type of protein is an odorant receptor?
GPCR
What are odorant-binding proteins important for?
help dissolve hydrophobic odorants so that they can bind ORNs
How many odorant receptors do ORNs express?
a given cell only expresses one type of odorant receptor
preferentially distributed w/in olfactory epithelium
How is the receptor map for olfaction organized?
organized in olfactory epi –> corresponds to matching zones in olfactory bulb
What attaches the olfactory bulb to the rest of the brain?
olfactory tract
What are the 5 layers of the olfactory bulb?
from cribriform plate up:
olfactory nerve layer
glomerular layer
external plexiform layer
mitral layer
granule cell layer
What do ORNs synapse with?
mitral and tufted cells
in a glomerulus in the glomerular layer
periglomerular cells interact with these cells in the glomerulus
What do periglomerular cells do?
branch exctensively in the glomerular layer
inhibitory to mitral and tufted cells
What cells are in the external plexiform layer?
tufted cells and dendrites of tufted cells
mitral cells
granule cells
How do mitral and tufted cells and granule cells interact?
dendrites of granule cells –> reciprocal synapses to modulate tufted and mitral cells
mitral and tufted cells –> excitatory synapses w/ granule cell dendrites
What is in the mitral cell layer?
thin layer containing large mitral cells
axons of other things also traverse this layer
What is in the granular cell layer of the olfactory bulb?
cell bodies of granule cells = interneuron
axons of other cells
What is special about granular cells in the olfactory bulb?
granule cells lack axons –> output is dendrodendritic GABAergic synapses w/ mitral and tufted cells –> inhibitory
Where does the olfactory bulb project?
axons of mitral and tufted cells –> lateral olfactory tract –> lateral olfactory stria –> cortex
some go to the anterior olfactory nucleus –> ducuss to other bulb = cross talk
*doesn’t go to thalamus for relay
What are the areas of the olfactory cortex (6)?
anterior olfactory nucleus
olfactory tubercle
piriform cortex
anterior cortical amygdaloid nucleus
periamygdaloid cortex
lateral entorhinal cortex
Where is information relayed after the olfactory cortex?
to insular and orbitofrontal cortices –> experience of flavors
dorsomedial nucleus of the thalamus
Lateral hypothalamus and hippocampus
Where does the lateral hypothalamus get olfactory input from?
piriform cortex and anterior olfactory nucleus
important for feeding behavior
Where does the hippocampus get olfactory input from and what happens there?
from entorhinal cortex –> links smell to learning and behavior
What is anosmia?
loss of smell
What is hyposmia or olfactory hypesthesia?
decreased sensitivity to odorants
nasal polyps = benign growths in nasal cavity or within sinuses
What N innervates taste on the anterior 2/3 of the tongue?
Facial N:
chorda tympani –> fungiform papillae and anterior foliate papillae
greater superficial petrosal N –> taste buds on soft palate
where are the cell bodies of CN VII for taste located?
geniculate ganglion
enter brainstem at pontomedullary jxn via intermediate N –> solitary tract –> target cells of solitary nucleus –> gustatory nucleus
What does CN IX innervate in taste?
lingual-tonsillar branch –> taste buds in vallate papillae and posterior foliate papillae (posterior 1/3)
cell bodies in petrosal ganglion
What does the vagus N innervate in taste?
superior laryngeal N –> taste buds of epiglottis and esophagus
cell bodies in the nodose ganglion
How do the cells innervating taste buds go to the brain?
VII: pontomedullary jxn via intermediate N –> solitary tract –> solitary nucleus –> gustatory nucleus
9 and 10: enter medulla –> solitary tract –> gustatory nucleus
How do 2nd and third order neurons of gustation travel?
1st orders synapse at gustatory nucleus of solitary nucleus
2nd: travel ipsi via central tegmental tract –> parvicellular ventral posteromedial nucleus (VPMpc) of thalamus
3rd: ipsi posterior limb of int capsule –> frontal operculum and anterior insula (area 3b = postcentral gyrus)
How would a lesion in the root of CN VII affect taste?
(or tumor in internal auditory meatus)
loss of taste perception from ant 2/3 of tongue on ipsi side
due to chorda tympani branch leaving CN VII distal to geniculate ganglion
ipsi facial paralysis
hyperacusis = paralysis of stapedius m
What would happen in damage to CN 7 distal to geniculate ganglion?
may or may not cause taste loss, depending on origin of chorda tympani branches
ipsi facial paralysis will be seen
What is aguesia?
complete loss of taste
What is parageusia/dysgeusia?
distortions in the perception of a taste
