special senses (taste and olfaction)

Question 1

what is olfaction

Answer 1

• chemoreceptors respond to smell similar to taste

- chemicals dissolve in mucous of nasal passages before binding to chemo. and registered as ‘smell’ by brain

Question 2

how does olfaction differ between humans and domestic animals

Answer 2

• superior olfactory ability

- greater SA of nasal cavity lining and size of olfactory region in brain

Question 3

what is the pathway of the olfactory nerves

Answer 3

1. nasal mucosa - olfactory epithelium
2. through cribriform plate of ethmoid bones
3. synapse at glomeruli from olfactory bulbs to mitral cells
4. olfactory tract to limbic system / primary olfactory cortex

Question 4

describe the anatomy of the nasal cavity

Answer 4

• ciliated pseudo stratified epithelium
• 3cm^2, olfactory cilia located on dendrites of sensory neurons
• nocic and temp receptors (ammonia, chilli)
• 1000 smell genes in nose (super sensitive)
• stronger smell = more odour molecules

Question 5

how are AP generated in the nasal cavity

Answer 5

1. odourant molecules dissolve and cross mucosal layer
2. bind to receptor coupled with G protein
3. activates G protein, cascade of events
4. influx of Ca and Na = depolarisation (decreases potential from -55 to -30)
5. AP

Question 6

describe the anatomy of papillae and tastebuds

Answer 6

• P: rounded protuberance on tongue, contain tastebuds

- TB: most respond to 2-4 taste qualities, bitter = most sensitive (protection), sugar / slat = pleasurable

Question 7

describe the receptors present in the mouth and pathways

Answer 7

• adapt quickly
• localisation = some regions more sensitive to certain tastes than others
  1. selectively bind to chemicals in food
  2. opening / closing of ion channels
  3. changes in electrical potential
  4. increase in Ca = neurotransmitter
  5. afferent nerve stimulated

Question 8

briefly describe the gustatory pathway to the brain

Answer 8

1. release of neurotransmitter AP
2. facial nerve (anterior 2/3 tongue) or glossopharyngeal nerve (posterior 1/3 tongue) or vagus nerve (back of mouth)
3. all travel to solitary nucleus of medulla
4. initiates PsNS reflexes (saliva / gastric secretion)
5. thalamic nucleus to gustatory cortex (parietal lobe) and limbic system