Physiology II: Taste and Smell

Taste and smell are chemoreceptors, generate neural signals on binding with … in their environment

particular chemicals

Sensations of taste and smell in association with food intake: influence flow of digestive juices and affect …

appetite

Taste and smell are chemoreceptors, generate neural signals on binding with … in their environment

particular chemicals

Sensations of taste and smell in association with food intake: influence flow of digestive juices and affect …

appetite

Sensations of taste and smell in association with food intake: induce pleasurable or objectional sensations - …

seek or avoid

Sensations of taste and smell in association with food intake: … for substances to be ingested

quality control

…: taste buds on the tongue

taste receptors

…: olfactory epithelium in nasal cavity

olfactory receptors

dissolved molecules bind to sites of the receptor membrane, causing … which lead to action potentials

receptor potentials

taste and olfactory receptors are …

continuously renewed

Taste receptor cells: primarily within tongue as …

taste buds

Taste bud consists of about 50 long, …, packages with supporting cells in an arrangement like slices of an orange

spindle-shaped taste receptor cells

…: coded by patterns of activity in various taste bud receptors

taste discrimination

Primary tastes: … (5)

salty, sour, sweet, bitter, umami

…: small opening in the taste bud, fluids in the mouth enter and come into contact with receptor cells

taste pore

Taste receptor cells are modified …

epithelial cells with microvilli

Plasma membrane of microvilli contains receptors for …

tastants (specific chemical signals)

Binding of tastants to receptor induced … in the receptor cell → neurotransmitter release (possibly ATP, serotonin) → firing in afferent nerve fiber

electrical signals

All tastes are … of five primary tastes

varying combinations

Salty: … (especially NaCl)

chemical salts

Salty transduction: … through specialized channels → depolarization

direct entry of Na+

Sour: acids containing … (citric acid in lemon)

free H+

Sour transduction: … → decrease in passive movement of positively charged K+ ions out of the cell → depolarizing receptor potential

H+ blocks K+ channels

Sweet: configuration of … (also artificial sweeteners)

glucose

Sweet transduction: … → cAMP → blockage of K+ channels → depolarization

G protein-coupled receptor

Bitter: diverse group of tastants → … (such as caffeine, nicotine) as well as toxic and poisonous substances

alkaloids

Bitter transduction: … → depolarization

GPCR gustducin cascade

Umami: savory, meaty taste - … (especially glutamate)

amino acids

Umami transduction: … → depolarization (distinctive taste of additive msg)

GPCR

The gut and airways have cells that have the same GPCRs and gustducin-activated pathways for tasting, they stimulate …, if they sense something toxic they trigger vomiting

motility and aid absorption of nutrients

Airways receptors detect toxic inhalants → … (sneezing and coughing)

protective reflexes

Taste cells synapse with primary sensory axons of cranial nerves …

facial nerve (VII), glossopharyngeal (IX), vagus (X)

…: conveys ordinary sensations in tongue including cold (peppermint) and pain (pepper and chili)

Trigeminal nerve (V)

Taste pathways: … → … → …

gustatory nucleus, thalamus, gustatory cortex

…: brainstem inside nucleus solitarius

gustatory nucleus

Gustatory cortex: … (2)

frontal operculum, insula

…: emotional and behavioral aspects

hypothalamus and amygdala

During quiet breathing odorants typically reach receptors only by … because olfactory mucosa above the normal path of airflow

diffusion

… enhances diffusion of odorants by drawing the air currents upward within the nasal cavity

sniffing

During eating odorants in th air pass from the mouth through …

pharynx

Olfactory mucosa contains: … (3)

olfactory receptors neurons, supporting cells, basal cells

…: primary sensory neurons, have dendrite exposed at surface of mucosa

olfactory receptor neurons

Olfactory dendrite contains … where odorant molecules bind, axons of olfactory receptor cells collectively form olfactory nerve

cilia

…: secrete mucus to help odorant molecules interact with receptor sites

supporting cells

…: precursors of new olfactory receptor cells, as olfactory neurons degenerate, basal cells divide to give rise to new receptor cells

Basal cells

Each receptor responds to only one discrete …

component of an odor

Appropriate scent signal to an olfactory receptor → … → cAMP-gated nonspecific cation channels → net Na+ and Ca2+ entry → depolarizing receptor potential → action potentials in afferent fibers

G protein, cAMP-dependent cascade

Separate components of an odor: sorted into …

different glomeruli

Glomeruli are sort of like …, one component per file

smell files

Odor discrimination is coded by … in the olfactory bulb glomeruli

patterns of activity

Each odorant activates … and … in response to its constituent odor componentents

multiple receptors, glomeruli

Odor discrimination takes place in the …

olfactory cortex

Olfactory projection pathway: one route goes to the … and …

medial temporal lobe, limbic system

Group of structures considered as primary olfactory cortex: … (largest component)

pyriform cortex

The route to the medial temporal lobe and limbic system provides coordination between … and …

smell, behavioral reactions

Limbic system is associated with: … (3)

motivation, emotion, memory

Second route of olfactory projections: … and … → conscious perception and discrimination of smell

thalamus, orbitofrontal cortex

Odorants rapidly cleared: … → very similar chemically to liver detoxification enzymes

odorant-clearing enzymes

…: detects pheromones, nonvolatile chemical signals passed subconsciously between individuals of the same species, reproductive and social behaviors

veronasla organ