Chemical Senses-(E2)

Chemoreceptors

sensory receptor selective for chemicals

What are the 5 flavors?

Umami

Bitterness

Sourness

Saltiness

Sweetness

Umami

signals amino acids/protein

Bitterness

signals potentially toxic/poisonous substances

Sourness

signals acids

Saltiness

signals ions-sodium

Sweetness

signals sugar/carbs

Why have so many subtypes of bitter receptors?

Many T2R bitter receptor subtypes allow us to detect a wide variety of potentially toxic compounds. 

Olfactory epithelium

contains receptor neurons

Olfactory bulb

first processing station; contains glomeruli

Olfactory tract

carries signals from bulb

Primary olfactory cortex

processes/interprets odors

adaptation

If you are exposed to a smell long enough, you stop smelling it!

Labeled-line hypothesis

One specific neuron/pathway represents one stimulus

Population coding

Central olfactory pathways decode the information from the whole neuronal population. Activity distributed over a large number of neurons.

Pharynx

connects the mouth with the nasal passages, allowing exchange of chemicals from food

taste buds

Foliate papillae

Fungiform papillae

Circumvallate papillae

NaCl

salty

Quinine

bitter

HCl (hydrochloric acid)

Sour

Sucrose

sweet

Transduction

process of environmental stimuli causing an electrical response

in a sensory receptor

Threshold concentration

The lowest concentration of a chemical (tastant) that can reliably evoke a taste response

Near threshold

Taste receptor cells and fibers may show relatively selective responses to particular tastes

Above the threshold

Increasing the concentration recruits more taste receptor cells.

and fibers, producing broader and more overlapping responses

Taste stimuli that directly pass through ion channels

SALT AND SOUR

Where are taste buds located

posterior wall of the pharynx and epiglottis

Thalamocortical Pathway

conscious perception

Hypothalamic Pathway

autonomic responses

Limbic/Amygdala Pathway

emotional associations with food

Olfactory epithelium

small, thin sheet of cells lining part of the nasal passages that contains olfactory receptor neurons

OLFACTORY RECEPTOR

sight of transduction

Supporting cells

helps produce mucus

Basal Cells

source of new receptor cell growth

Every 4 to 8 weeks

Glomeruli

cluster of neurons in the olfactory bulb that receive input from olfactory receptor neurons