Chemical senses

Smell and taste

Olfactory epithelium

Organ of smell

Smell genes

Encode for a specific receptor protein

Allows us to differentiate odors

Olfactory nerve

Made up of axons from olfactory sensory neurons

Olfactory signal transduction

1. Odorant binds GPCR on olfactory sensory neuron

2. Activates G protein

3. Activates adenylyl cyclase

4. Increases cAMP

5. Na⁺/Ca²⁺ channels open

6. Depolarization

7. Action potential

8. CN I

9. Olfactory bulb

Olfactory receptor type

Metabotropic, specifically GPCR

Taste buds

Found in most papillae

Gustatory epithelial cells

Receptor cells for taste

Basal cells

The stem cells for taste that replace gustatory epithelial cells

5 Basic tastes

1. Sweet

2. Umami

3. Bitter

4. Sour

5. Salty

Mechanisms for salty

NA influx channels

Directly depolarizes gustatory epithelial cells

Mechanisms for sour

Mediated by H+, which blocks K+ leak channels

Causes depolarization

Mechanisms for bitter, sweet, and umami

G protein coupled receptors

Gustducin

A common G protein that taste receptors are coupled to

1. Activation causes the release of Ca

2. Cation channels in the plasma membrane open

3. Cell depolarizes

4. Release neurotransmitter ATP