Ionotropic vs Metabotropic Receptors & 2nd Messenger System

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Compare and contrast ionotropic and metabotropic receptors. Describe in detail the second messenger system

What is the general functional organization of a receptor?
For a loose, practical analogy, think of the neuron as a computer with a touch-screen that contains a group of different software program icons. Your finger represents the neurotransmitter and each icon represents a different receptor. Depending upon which icon (receptor) your finger (neurotransmitter) contacts, a specific software program is initiated ( a functional change), which will carry out its own set of instructions and produce a particular result (a biological response). To make the analogy a bit more accurate, different computer touch-screens (neurons) would contain different combinations of software icons (receptors), and (I don't know how you would make this work) each of your fingers, representing different transmitters, would only be able to activate a specific set of icons (receptors).
In essence, membrane receptors represent a transmembrane signalling system of the neuron with an analogous function to that of sensory receptors on our bodies. In both cases, a signal from outside is converted into a different form of information inside. In the case of the body, an external physical stimulus impinging upon a sensory receptor is converted into action potentials within a particular neurosensory pathway. In the neuron, the binding of an exogenous chemical ligand with a membrane receptor activates a particular sequence of neurochemical changes within the neutron.

Here is a more concrete, scientific-sounding definition of a receptor: A receptor is a protein or protein complex, within the membrane, that has a binding site (or sites) that binds a neurotransmitter externally and has some kind of trans-membrane or intra-cellular domain that can signal that the transmitter is bound. The binding activates some kind of primary effector which produces some kind of change in the functional status of the neuron (e.g. opening of an ion channel, etc.) which leads to the biological response of the neuron (e.g. depolarization, hyperpolarization, etc.).

What are the major functional classes of receptors?
There are two major functional classes of receptor: ionotropic and metabotropic.
An ionotropic receptor, when activated, directly ...