Olfactory and Gustatory Pathways

Question 1

5 taste qualities?

Answer 1

salty, sweet, sour, umami, bitter (all other detection is smell)

Question 2

where are tastebuds located?

Answer 2

within crevices of pappillae

Question 3

what are three cell types in the pore of taste cell?

Answer 3

taste receptor cell
basal cell (regenerative cell, will turn over every 7-14 days)
supporting cell

• stereocilia are located at the apical portion of the pore

Question 4

how is taste perceived?

Answer 4

• chemical stimuli will directly enter taste cell via ion channels
• because they are positively charged they can depolarize the taste cell, causing an influx of Ca2+ and release of NT
• more complex molecules will bind apically located receptors which will stimulate a second messenger which will depolarize the cell.
• NT will activate the primary affarent nerve

Question 5

how many taste cells are located in a taste bud? innervation?

Answer 5

• 50-100.
• each taste bud is innervated by CN VII, IX, or X
• taste cells do not have axons and are epithelial in origin. However they do respond to chemical stimuli by depolarizing their membrane.
• Some modalities have labelled line coding, while others have cross fiber coding.

Question 6

Which CNs supply which part of the tongue?

Answer 6

CN VII = ant 2/3 of tongue (foliate and fungiform)

CN IX = post 1/3 of tongue (circumvallate and foliate)

CN X = epiglottis

Question 7

where do primary affarents of taste buds project?

Answer 7

all project ipsilaterally to the rostral portion of the nucleus of the solitary tract
Note: oral trigeminal affarents also project to NST - but they are caudal to taste projection

Question 8

pathway of taste from anterior 2/3 of tongue and soft palate?

Answer 8

primary affarents arise from ipsilateral rostral solitary nucleus. They travel out on CN VII, and cell body is located in geniculate ganglion.

• greater petrosal n. projects to soft palate
• corda tympani n. projects to ant. 1/3 of tongue

Question 9

pathway of taste from posterior 1/3 of tongue.

Answer 9

taste is received and transmitted along CN IX. Cell body located in inferior ganglion of glossopharyngeal (petrosal ganglion). ultimately CN IX travels back to ipsilateral rostral portion of solitary nucleus

Question 10

pathway of taste from epiglottis?

Answer 10

• travels along CN X.
• cell body located in nodose ganglion (of IG of X)
• travels to rostral portion of solitary tract

Question 11

where do 2 order affarents go from the solitary tract?

Answer 11

second order neurons will ascend.

• will project to dorsal montor nucleus of X (stimulates Gag reflex)
• will ascend and synapse onto neurons in the IPSILATERAL ventral posteromedial nucleus of the thalamus (VPM).
• they will then project out ipsilaterally to the primary gustatory cortex (anatomical: insular cortex)

Question 12

insular cortex functional name?

Answer 12

primary gustatory cortex

Question 13

what are two pathways for odorants to enter into the nasal cavity?

Answer 13

1. orthonasally: smoke, food, flowers - this is smelling the environment
2. retronasally: odors released from food while we are eating

Question 14

smells

Answer 14

10,000 different smells can be smelled.
- our olfactory system is not that evolved.
- Many molecules may be required to produce a
sensation that we consider one odor
- Although the perception of some odors involves manymolecules, the olfactory system can discriminate between some VERY closely related molecules

Question 15

olfactory receptor neurons location?

Answer 15

• located in the lateral mucosal wall of the superior portion of the nasal septum.
• cilia projecting out of neuron has olfactory receptors. These are true bipolar neurons.
• cilia project into nasal cavity and bind odorants, causing the axon to depolarize and the neuron to transmit APs

Question 16

how are 10,000 odors detecteed?

Answer 16

• olfactory cells are embedded in an eptihelium in a mucus layer.
• each odor receptor responds to multiple odorants
• Each odorant simulates multiple receptors
• A particular odorant activates a pattern of glomeruli
• Thus the code for odor perception is a combinatorial code

Question 17

projection pathway of olfactory neuron?

Answer 17

• cilia respond to odor, activate olfactory receptor cells, which send an AP.
• the olfactory neurons travel together in “olfactory filia” and join axons that pass through the cribiform plate.
• not the olfactory neuron has direct axis to CNS, possible route for viral invasion of the brain

Question 18

anosmia

Answer 18

without olfaction

• can occur due to mvmt in cranial vault - can cause olfactory neurons to be injured at cribiform plate
• these are some of the only neurons though that can regenerate.

Question 19

what forms olfactory tract?

Answer 19

different olfactory neurons will wire up to the flomeruli in certain patterns and synapse on mitral cells. mitral cell axons will run in the olfactory tract

Question 20

what is the central pathway of olfactory system?

Answer 20

• most is headed to IPSILATERAL cx. for conscious perception of smell *

1. mitral cell axons from the olfactory tract first synapse in anterior olfactory nuclei located within the tract.
2. olfactory tubercle (anterior perforated substance)
3. piriform cortex
4. amygdala (emotional)
   5 periamygdaloid cx.
5. entorhinal cx (memories of smell)
   - does not go to thalamus to get to cerebral cx.

Question 21

what does orbitofrontal cx do?

Answer 21

receives olfactory, taste and somatosensory info and integrates it to make flavors
= “flavor cortex”
- primary olfactory is sent here along with SS and taste.

Question 22

Dysomia

Answer 22

incorrect smell - things smell different than they should

Question 23

anosmia

Answer 23

lack of ability to smell

Question 24

hyposmia

Answer 24

decreased ability to smell

Question 25

phantosmia

Answer 25

“hallucinated smell” -often unpleasant

• seizure activity in olfactory processing areas (parahippocampal gyrus and related structures)
• often precedes an epileptic attack – aura before a seizure
• if focal point of seizure is near uncus – in the aura will come a phantosmia smell described as being unpleasant
• Piriform cortex electrical stimulation causes olfactory sensations. Seizures could be a cause of olfactory hallucinations or dysosmia.

Question 26

hyperosmia

Answer 26

an abnormally acute sense of smell

- i.e. estrogen can cause hyperosmia

Question 27

conductive olfactory defecit

Answer 27

things that prevent odorants from reaching olfactory epithelium
e.g., nasal polyps, septal deviation, inflammation

Question 28

sensorineuroal olfactory deficit

Answer 28

things that damage the olfactory receptor neurons or parts of the olfactory CNS
e.g., head injuries or neurodegenerative conditions such as Parkinson’s disease or Alzheimer’s diseas. Olfactory fila may be torn loose from olfactory bulb by head trauma. Some patients suffer permanent damage to olfactory receptor neurons after a severe upper respiratory infection.