Correction: Salty taste is in fact in Type I cells which don't have a synapse!The diagram depicts the signal transduction pathway of the sour taste. Object A is a taste bud, object B is a taste receptor cell within object A, and object C is the neuron attached to object B. 
I. Part I is the reception of hydrogen ions or sodium ions. 
1. If the taste is sour, H+ ions, from an acidic substances, pass through their specific ion channel. Some can go through the Na+ channels. If the taste is salty Na+, sodium, molecules pass through the Na+ channels. Depolarization takes place 
II. Part II is the transduction pathway of the relay molecules.
2. Cation, such as K+, channels are opened. 
III. Part III is the response of the cell. 
3. An influx of Ca+ ions is activated.
4. The Ca+ activates neurotransmitters. 

5. A signal is sent to the neuron attached to the taste bud.
Own work &amp; Purves, Dale. Taste Receptors and the Transduction of Taste Signals. U.S. National Library of Medicine, n.d. Web. May-June 2015.
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