In pharmacology, receptors can be divided into 4 general groups:

1. Ion channels:

2. G protein coupled receptors

3. Receptor tyrosine kinase

4. Intracellular hormone receptors: likeĀ  the glucocorticoid receptor

The video animation below shows the activation of a ionotropic receptor or ligand-gated ion channel (LGIC):

An excerpt on the topic from Katzung’s textbook:

Ligand-Gated Channels

Many of the most useful drugs in clinical medicine act by mimicking or blocking the actions of endogenous ligands that regulate the flow of ions through plasma membrane channels. The natural ligands include acetylcholine, serotonin, GABA, and glutamate. All of these agents are synaptic transmitters.

Each of their receptors transmits its signal across the plasma membrane by increasing transmembrane conductance of the relevant ion and thereby altering the electrical potential across the membrane. For example, acetylcholine causes the opening of the ion channel in the nicotinic acetylcholine receptor (AChR), which allows Na+ to flow down its concentration gradient into cells, producing a localized excitatory postsynaptic potential-a depolarization.