This video will cover the physiology of the bitter sweet umami gustatory cell.
The reason we can rope all 3 of these tastes together is because they all go through a very similar physiology
the major difference between the 3 is the type of GPCR they activate(so in other words, there is a specific GPCR for each of the 3 different tastes.)
But I'm going to treat this taste cell as if I'm doing physiology for all 3 tastes.

So first things first, you need to eat something to get the tastants in your mouth.
This little greenish yellow sun is representing our bitter sweet or umami tastant.
The tastetant binds to the GPCR and activates it to associate with the subunits inside of the cell
The alpha subunit (which is here in yellow) is the most important because it supplies the main physiological changes that occur in the cell.
So when the alpha subunit is activated, it in turn goes and activates the Enzyme called Phospholipase C.
Phospholipase C is responsible for Cleaving PIP2.
PIP2 is a specialized phospholipid that hides out in the cell membrane.
When phospholipase C comes into contact with PIP2 it cleaves it into a couple of products (which are DAG and most importantly inositol triphosphate or IP3)
We wont give any attention to DAG, but IP3 is responsible for causing a calcium release from the smooth ER.
As you should know by now, When the calcium exits the smooth ER in any cell, it causes a whole host of changes.
Within the bitter sweet and umami pathways, the calcium mainly causes the release of ATP.
ATP then acts as the neurotransmitter needed to activate the Gustatory afferent Neuron which then tells your gustatory cortex of the brain that you are tasting something.