Neuroanatomy of Gustation and Olfaction

Question 1

What is the role of olfactory receptor neurons?

Answer 1

Allows you to recognize thousands of air-borne odors even at extremely low concentrations

Question 2

What is the significance of thin nasal bones?

Answer 2

Thin bones allows the olfactory receptor neurons to be sensitive to facial trauma

Question 3

Describe the taste capabilities of the gustatory system

Answer 3

Very limited range

Sweet, salty, sour, bitter and umami (important for identifying amino acids)

Question 4

What allows you to accept/reject foods and taste things other than the four basic tastes

Answer 4

Different combination of taste receptors

Question 5

What is the significance of the olfactory bulb and tract?

Answer 5

Olfactory receptors synapse at the bulb in the cribiform plate and processes odors.
Tract transmits sensory info to the brain

Question 6

*Anatomy of the cribriform plate

Answer 6

The bulb sits here. Located at rostral end of the olfactory sulcus and anterior cranial fossa

Question 7

*Anatomy of olfactory receptor neurons

Answer 7

Located on the roof of nasal cavity/inferior surface of cribriform plate, along nasal septum and medial wall of superior nasal conchae

Question 8

What is CN I?

Answer 8

Olfactory receptor Neuron. Has a single dendritic process that receives info from envt. Receptors are in the olfactory mucosa of the superior nasal cavity

Question 9

What is the importance of ducts and glands?

Answer 9

Keep the olfactory epithelium moist

Question 10

*What is the role of the supporting cells?

Answer 10

Surround the olfactory nerve bodies. Have receptors extending to the olfactory epithelium to catch smell molecules

Question 11

Cilia on ORNs

Answer 11

Nonmotile and contain GPCR (ligand gated) receptors. Ligand binding = signal sent to olfactory bulb

Question 12

What is the significance of the lamina propria?

How about Basal cells?

Answer 12

• Holds immune cells (important since the mucosa is exposed to external envt)
• act as stem cells for ORNs and supporting cells

Question 13

What is the significance of Brush cells?

How about Mucus

Answer 13

• ciliated columnar epithelial cells

- made and secreted by glands and ducts in the Olfactory epithelium

Question 14

Describe how the smell molecules reach the olfactory bulb

Answer 14

Smell molecule ligand binds to GPCR on ORN > contact mucus layer on olfactory epithelium and interacts with odorant binding proteins in the mucus > adenyl cyclase activation = increase cAMP > ion channels open and increase in Ca and Na influx > action potential to the olfactory bulb

Question 15

*Describe the organization of the olfactory bulb

Answer 15

An ORN GPCR accepts a particular smell ligand. In the bulb the ORNs are grouped according to the ligand they respond to. Different ORN combination results in smelling different things

Question 16

What is the significance of granule cell layer?

Answer 16

Deepest of the olfactory bulb. Has granule cells which are the interneurons of the olfactory bulb that help regulate other cells

Question 17

*What is the significance of the mitral cell layer?

Answer 17

Has mitral cell bodes and axons of the tufted cells that carry sensory info received from the ORNs and transmit it to the brain

Question 18

What is the importance of the External plexiform layer?

Answer 18

Has dendrites of the tufted, mitral and granule cells. Cross talk between these cells happen in this layer.

Question 19

What molecule do granule cells use to modulate tufted and mitral cell output?

Answer 19

GABA (lowers mitral/tufted cell activity)

Question 20

*What is the importance of the glomerular cell layer?

Answer 20

ORNs synapse to the olfactory bulb in this layer

Question 21

*What is the importance of the olfactory nerve layer?

Answer 21

Has the ORN axons that penetrate the cribriform plate

Question 22

**What is the role of centrifugal fibers?

Answer 22

Carry info from brain to bulb via the anterior commissure. Regulates feedback loops

Question 23

What is the olfactory glomeruli? Describe the nature of the ORNs synapsing on the glomerulus

Answer 23

ORNs will synapse on tufted and mitral cells in the glomerulus.
One glomerulus has lots of ORNs sensitive to the same odor molecule synapsing but ORN only synapses on 1 glomerulus.

Question 24

How do you adapt to smell?

Answer 24

Negative feedback of granular cells inhibit the propagation of info by mitral and tufted cells when you smell something for long enough

Question 25

How is info about olfaction transmitted to the brain?

Answer 25

Via mitral/tufted cells to the lateral olfactory tract

Question 26

Importance of olfactory projections to the hippocampus, amygdala and dorsomedial thalamic nucleus

Answer 26

Hippocampus - memory
Amygdala - recognize danger and fear
Dorsomedial nucleus - secondary projection from the olfactory cortex for further info processing

Question 27

Draw the different projections of olfactory info from the lateral olfactory tract

Answer 27

Ok

Question 28

What is the paleocortex and neocortex and what are their significance?

Answer 28

Paleocortex (primitive cortex) where the olfactory cortex is. Sends projections to other areas (neocortex areas)
Neocortex helps discriminate odors

Question 29

Significance of the orbitofrontal cortex?

Answer 29

Where integration of smell and taste occur

Question 30

Where are taste buds found?

Answer 30

All over the oropharyngeal cavity, not just the tongue

Question 31

Describe the pathway of taste perception

Answer 31

Taste molecules diffuse through taste pore and bind to receptors on apical microvilli > cell depolarize or hyperpolarize > action potential relayed to afferents > fibers from the facial nerve (chorda tympani) synapse to the solitary tract > solitary nucleus > gustatory nucleus (rostral portion of the solitary nucleus)

Question 32

Importance of the chorda tympani and soft palate

Answer 32

• Innervates the fungiform papillae and anterior foliate papillae (anterior 2/3)
• taste buds here are innervated by the greater superficial petrosal nerve (also from CN VII)

Question 33

Importance of the pontomedullary junction and geniculate ganglia

Answer 33

Afferents from facial nerve carry info and enter the brainstem here
Where sensory cell bodies of CN VII are. Carry taste to the rostral solitary nucleus (gustatory nucleus)

Question 34

Tongue innervation

Answer 34

Anterior 2/3 = lingual n. (from CN V) for sensation and chorda tympani for taste
Posterior 1/3 = CN IX

Question 35

Which papillae does VII innervate?
Which papillae does IX innervate?
Which does X innervate?

Answer 35

Filiform, fungiform and anterior foliate
Posterior foliate, vallate
Median glosso-epiglottic fold

Question 36

*Describe the gustation pathway

Answer 36

Taste molecule binds receptors on papillae > depolarize the taste bud receptors > AP > travels to solitary tract > solitary nucleus > ipsilateral central tegmental tract > parvicellular ventral posteromedial nucleus > ipsilateral posterior limb of internal capsule > frontal operculum and anterior insular cortex > Brodmann area 3b > Lateral posterior orbitofrontal cortex with all other action potentials

Question 37

What is anosmia?

Hyposomia?

Answer 37

• loss of smell

- decreased sensitivity to odorants

Question 38

What is ageusia?
Hypoguesia?
Parageusia/dysgeusia

Answer 38

Complete loss of taste. Rare since many CNs ( VII , IX and X) carry taste info
Decreased taste sensitivity
Altered taste perception (due to drug use)

Question 39

Lesions of CN VII

Answer 39

Can be caused by vestibular schwannoma in the Internal Auditory meatus by compressing the chorda tympani. Results in loss of taste in anterior 2/3 of tongue on ipsilateral side, ipsilateral facial paralysis, hearing loss (due to stapedius), impaired gland secretion

Question 40

Lesion of distal geniculate ganglion?

Answer 40

Facial nerve fibers synapse here first. Facial paralysis possibly with or without taste loss