Taste - Chemoreception

Gustation

taste

olfaction

smell

5 basic taste qualities

salty, sour, sweet, bitter, and umami (meaty)

tongue structure

papillae

• foliate: senses of bolds on back and sides of tongue

• circumvallate: shaped like fat mounds in a trench located on the back of tongue

• fungiform: shaped like mushroom and found on sides and tip of tongue

  • these contain your taste buds

Salty taste transduction

• Na+ through ion channel, depolarization, opens Ca2+ channels

  • NT: serotonin

sour taste transduction

• Sour: H+ through ion channel, depolarization, opens Ca2+ channels

  • Nt serotonin

Sweet taste transduction

• Sweet: binds to membrane receptors, G proteins activated, close K+ channels

  • NT: ATP

Bitter taste transduction

Bitter: binds to membrane receptors, G proteins activated, Ca2+ entry

• NT: ATP

umami taste transduction

• Umami: meaty, brothy, savory assoc. w/ MSG – same mechanisms as sweet

neural pathways

sugar/salt is eaten, the taste bud goes through the process we just talked abt, the NT is sent through sensory neurons to the sugar/salt interneurons in the CNS

• more sugar/salt, the more APs there are sent to the brain

Gustatory pathway

signals from taste cells trave along a set of pathways

• facial nerve and glossopharyngeal nerve

• medulla oblongata: initiate PNS refflexes to trigger saliva and gastric secretion

  • project this info to thalamus and gustatory cortex

  • fibers also project to hypothalamus and limbic system (enjoyment)

chemosensory coding

coding in the sensory system could theoretically follow

• labeled line coding

• across fiber pattern/ensemble coding

labeled line coding

each receptor responds to limited range of stimuli and sends direct line to brain

• receptors are narrowly tuned: specialist

  • ex: cell phone, you calling someone

• receptor input: sweet to CNS: labled line to Line decoder output “sweet”

  • straight forward straight line

across fiber pattern/ensemble coding

each receptor respons to wider range of stimuli and contributes to perception of each of them

• receptors are less narrowly tuned: generalists

• receptor input: sweet to CNS: pattern code to pattern decoder output: “sweet”

  • not a straight line

• neurons (type A-D) are sensitive to many diff stimulus, but show highest sensitivity to a few stimuli

  • in contrast: labeled line coding