Neuroanatomy of Taste and Olfaction

Question 1

What are the 5 basic tastes?

Answer 1

sweet

salty

sour

bitter

umami - ID of amino acids

Question 2

Where does the olfactory bulb lie?

Answer 2

on the cribiform plate of the ethmoid bone

Question 3

Where are olfactory receptor cells located?

Answer 3

in the roof of nasal cavity and on inferior surface of cribriform plate

along nasal septum and medial wall of superior turbinate

Question 4

What type of protein is an odorant receptor?

Answer 4

GPCR

Question 5

What are odorant-binding proteins important for?

Answer 5

help dissolve hydrophobic odorants so that they can bind ORNs

Question 6

How many odorant receptors do ORNs express?

Answer 6

a given cell only expresses one type of odorant receptor

preferentially distributed w/in olfactory epithelium

Question 7

How is the receptor map for olfaction organized?

Answer 7

organized in olfactory epi –> corresponds to matching zones in olfactory bulb

Question 8

What attaches the olfactory bulb to the rest of the brain?

Answer 8

olfactory tract

Question 9

What are the 5 layers of the olfactory bulb?

Answer 9

from cribriform plate up:

olfactory nerve layer

glomerular layer

external plexiform layer

mitral layer

granule cell layer

Question 10

What do ORNs synapse with?

Answer 10

mitral and tufted cells

in a glomerulus in the glomerular layer

periglomerular cells interact with these cells in the glomerulus

Question 11

What do periglomerular cells do?

Answer 11

branch exctensively in the glomerular layer

inhibitory to mitral and tufted cells

Question 12

What cells are in the external plexiform layer?

Answer 12

tufted cells and dendrites of tufted cells

mitral cells

granule cells

Question 13

How do mitral and tufted cells and granule cells interact?

Answer 13

dendrites of granule cells –> reciprocal synapses to modulate tufted and mitral cells

mitral and tufted cells –> excitatory synapses w/ granule cell dendrites

Question 14

What is in the mitral cell layer?

Answer 14

thin layer containing large mitral cells

axons of other things also traverse this layer

Question 15

What is in the granular cell layer of the olfactory bulb?

Answer 15

cell bodies of granule cells = interneuron

axons of other cells

Question 16

What is special about granular cells in the olfactory bulb?

Answer 16

granule cells lack axons –> output is dendrodendritic GABAergic synapses w/ mitral and tufted cells –> inhibitory

Question 17

Where does the olfactory bulb project?

Answer 17

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

Question 18

What are the areas of the olfactory cortex (6)?

Answer 18

anterior olfactory nucleus

olfactory tubercle

piriform cortex

anterior cortical amygdaloid nucleus

periamygdaloid cortex

lateral entorhinal cortex

Question 19

Where is information relayed after the olfactory cortex?

Answer 19

to insular and orbitofrontal cortices –> experience of flavors

dorsomedial nucleus of the thalamus

Lateral hypothalamus and hippocampus

Question 20

Where does the lateral hypothalamus get olfactory input from?

Answer 20

piriform cortex and anterior olfactory nucleus

important for feeding behavior

Question 21

Where does the hippocampus get olfactory input from and what happens there?

Answer 21

from entorhinal cortex –> links smell to learning and behavior

Question 22

What is anosmia?

Answer 22

loss of smell

Question 23

What is hyposmia or olfactory hypesthesia?

Answer 23

decreased sensitivity to odorants

nasal polyps = benign growths in nasal cavity or within sinuses

Question 24

What N innervates taste on the anterior 2/3 of the tongue?

Answer 24

Facial N:

chorda tympani –> fungiform papillae and anterior foliate papillae

greater superficial petrosal N –> taste buds on soft palate

Question 25

where are the cell bodies of CN VII for taste located?

Answer 25

geniculate ganglion

enter brainstem at pontomedullary jxn via intermediate N –> solitary tract –> target cells of solitary nucleus –> gustatory nucleus

Question 26

What does CN IX innervate in taste?

Answer 26

lingual-tonsillar branch –> taste buds in vallate papillae and posterior foliate papillae (posterior 1/3)

cell bodies in petrosal ganglion

Question 27

What does the vagus N innervate in taste?

Answer 27

superior laryngeal N –> taste buds of epiglottis and esophagus

cell bodies in the nodose ganglion

Question 28

How do the cells innervating taste buds go to the brain?

Answer 28

VII: pontomedullary jxn via intermediate N –> solitary tract –> solitary nucleus –> gustatory nucleus

9 and 10: enter medulla –> solitary tract –> gustatory nucleus

Question 29

How do 2nd and third order neurons of gustation travel?

Answer 29

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)

Question 30

How would a lesion in the root of CN VII affect taste?

Answer 30

(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

Question 31

What would happen in damage to CN 7 distal to geniculate ganglion?

Answer 31

may or may not cause taste loss, depending on origin of chorda tympani branches

ipsi facial paralysis will be seen

Question 32

What is aguesia?

Answer 32

complete loss of taste

Question 33

What is parageusia/dysgeusia?

Answer 33

distortions in the perception of a taste