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Taste and Smell
Taste and smell are involved with specific
receptor cells called chemoreceptors
• respond to chemicals in
an aqueous solution
• food dissolved in saliva
• airborne chemicals
dissolved in mucous
membrane
The Tongue
Why are they important?
Salty- metallic ions
Sweet- sugars
Bitter- alkaloids (Bases)
Sour- H+ (acids)
Umami- savory
Facial nerve
(afferent) 2/3 anterior
portion of tongue
Glossopharyngeal
posterior 1/3 of tongue
Vagus nerve- few
taste buds on epiglottis
an pharynx
These afferent fibers
synapse in
medullathalamus
gustatory cortex in
parietal lobes and
fibers to hypothalamus
in limbic system
Taste triggers reflex involved in digestion;
causes an increase of saliva in mouth
(amylase) and gastric juice in stomach
acids cause strong salivary reflex
bad tasting food causes gagging or
reflexive vomiting
taste can change over time
taste is 80% smell
Mouth also contains:
Thermoreceptors
Mechanoreceptors
Nociceptors- sensitive nerve fibers that are aware of painful
stimuli
• Specific chemicals cause specific
patterns of neurons to fire
• Smell not as good as animals
• Humans can distinguish 10,000 or so
chemicals
• Olfactory fatigue or adaptation
• Old people lose sense of smell
• What we really smell is pain: ex. chili,
ammonia, menthol (cold)
Olfactory
epithelium
Olfactory tract
Olfactory bulb
Nasal
conchae
Route of
inhaled air
Olfactory
tract
Mitral cell (output cell)
Glomeruli
Olfactory bulb
Cribriform plate of ethmoid bone
Filaments of olfactory nerve
Olfactory
gland
Lamina propria connective tissue
Axon
Basal cell
Olfactory receptor cell
Olfactory
epithelium
Supporting cell
Mucus
Dendrite
Olfactory cilia
Route of inhaled air
containing odor molecules
Olfactory neurons are the only neurons
that replace themselves
loss of sense of smell
• Lose sense of smell  lose taste
• Cranial nerve trauma
• May be genetic or a cold (mucus), allergy,
zinc deficiency
• Phantosmia: olfactory hallucinations;
may be psychological ex. rotting meat
smell
• Olfactory auras- prior to epileptic attack