Gustatory Pathways

Question 1

What are the 5 different tastes and what do they tell us?

Answer 1

Sweet - nutrition
Sour - H+ electrolyte balance
Salty - Na+ 
Bitter - helps us detect things that are toxic, good protective reflex
Unami (savory) - nutrition

Question 2

How can bitter influence a patient’s eating?

Answer 2

Response to bitter can be a conditioned taste aversion.

• Learning to pair food with malaise
• Can be problematic for patients undergoing cancer drug therapy
• Patients learn to avoid food that tastes bad bc of drugs

Question 3

How is a taste bud organized?

Answer 3

It is a traditional special sense cell - receptor is not on the primary afferent.

• You have 50-150 taste receptor cells per taste bud
• Each receptor only detects 1/5 tastiest
• Taste bud receptor cells turn over every 10 days

Question 4

How are Bitter, Sweet and Unami transduced?

Answer 4

1. Receptor protein activated
2. G protein - Gustducin activated
3. 2nd messenger system
4. Opens channel & causes depolarization
5. Opens VG Ca2+ channels or release of Ca2+ from intracellular stores
6. Releases ATP (NT)

Question 5

How are sour and salty transduced?

Answer 5

1. Receptor protein activated.
2. Sour - H+ ions flow in and close a K+ channel
   Salty - Na+ goes directly in through an Na+ channel
3. Depolarization of the cell occurs.
4. Opens VG Ca2+ channels or release of Ca2+ from intracellular stores
5. Releases 5HT - Serotonin (NT)

Question 6

What is the name of the inability to identify taste and smell?

Answer 6

Agnosia

Question 7

What is an -osmia disorder?

Answer 7

Olfactory disorder

Question 8

What is an -gusia disorder?

Answer 8

Gustatory disorder

Question 9

What is anosmia or agusia?

Answer 9

Complete absence of smell or taste.

Question 10

What is hyposmia or hypogusia?

Answer 10

Reduced perception of smell or taste.

Question 11

What is hyperosmia?

Answer 11

Increased perception of smell (olfactory)

Question 12

What is dysosmia or dysgusia?

Answer 12

Distortion or perversion to smell or taste.

Question 13

What is Cacosmia or Cacogusia?

Answer 13

It is extremely unpleasant perception (revolting) of smell or taste.

Question 14

What do people with anosmia usually complain about?

Answer 14

Agusia as well.

Question 15

What is a peripheral cause of smell or taste problems?

Answer 15

Chemicals don’t reach the receptors or are altered on the way to the receptor.

• Olfaction: too much mucous, inflammation, foreign body
• Gustation: not enough saliva/dry mouth (can’t dissolve chemical so it can’t reach taste bud), too thick of secretions (cystic fibrosis), thrush

Question 16

What is a neuroepithelial cause of smell or taste problems?

Answer 16

Damage or absence of receptor cells, or damage to their processes or any aspect of the transduction mechanism.

• Olfaction: head trauma, toxins/cocaine/drugs
• Gustation: burning tongue, toxins/drugs

Question 17

What is a central cause of smell or taste problems?

Answer 17

Damage or malfunction in any of the central pathways.

• Hallucinations and loss of discrimination are usually of central origin
• Parkinsons, Epilepsy, Alzheimer’s disease, tumors
• Bact. meningitis in Pons can cause this too

Question 18

What innervates taste buds on the larynx and epiglottis?

Answer 18

Vagus nerve - these buds are involved more in chemical detectants - irritants control their response - CN X

Question 19

What innervates the back 1/3 of the tongue?

Answer 19

Glossopharyngeal - CN IX (primary afferent)

Question 20

What innervates taste perception for the front 2/3 of the tongue?

Answer 20

Facial nerve - Chorda tympani (primary afferents of taste)

Question 21

What innervates the touch/temp. perception in the front 2/3 of the tongue?

Answer 21

Trigeminal - V3 - Lingual Branch

Question 22

When the primary afferents of taste sensation reach the CNS, what do they travel through?

Answer 22

Solitary tract and end in the nucleus of the solitary tract (mostly rostral end)

Question 23

What is the pathway from taste buds to gustatory cortex?

Answer 23

1. Taste buds
2. CN VII, IX & X
3. Solitary Tract
4. Solitary Nucleus
5. Thalamus (VPM ventral posteromedial nucleus)
6. Internal Capsule
7. Gustatory cortex (insula)

Question 24

What is the pathway fro CN IX and X in the visceral portion of the gustatory pathway?

Answer 24

1. Visceral afferents
2. CN IX & X
3. Solitary tract
4. Solitary nucleus
5. Hypothalamus or Preganglionic Autonomics

Question 25

What does the vagus nerve do in terms of chemical monitoring?

Answer 25

It sends info from the GI tract and circulatory system chem. monitoring systems via the vagus nerve to the brainstem from within the body.

Question 26

How do afferent fibers from thoracic and abdominal viscera reach the brainstem?

Answer 26

Through the vagus (and bit of glossopharyngeal) nerves.

Question 27

Where does the vagus nerve send visceral information?

Answer 27

It terminates in the nucleus of the solitary tract.

Question 28

What happens to the visceral information that the vagus sends to the NST?

Answer 28

The NST participates in visceral reflexes (heart rate, digestions - via the dorsal motor nucleus of X)

Question 29

What is the role of the dorsal motor nucleus of X in parasympathetic innervation of thoracic and abdominal viscera?

Answer 29

It can change heart rate (dec. usually in para) and digestion (inc. usually in para).

Question 30

How does the gag reflex work?

Answer 30

1. Wall of one side of pharynx is touched (UNILATERAL)
2. CN IX (glossopharyngeal) sends sensory afferent fibers to nucleus ambiguous
3. Efferent motor output to pharyngeal and laryngeal muscles is via CN X (Vagus) and is BILATERAL

Question 31

What does the nucleus ambiguous contain?

Answer 31

Motor output to the pharynx and larynx - activated when you gag or cough