What are the two mechanisms regarding epoxide ring opening?

Epoxide ring opening mechanisms occur under two conditions, and this pertains to the reagents involved in the reaction. This can either occur under basic or acidic conditions. At which point I would then show the reagents for each, and the steps to how each of the mechanisms follow...(Protonation as the first step of the acid condition mechanism... etc.)

How can I effectively learn a subject with dense and complicated material, such as Organic Chemistry?

A key component to studying dense subjects like Organic Chemistry is to construct condensed study sheets. Instead of having numerous mechanisms, principles, and reactions on many sheets of paper, organize and categorize them together, and write them neatly and condensed on maybe one or two sheets of plain printer paper. Also, use various colored pens in order to create distinctions between reagents, what is being removed, side-chains that are being added on, etc.

What are the various plexus divisions amongst the body's spinal nerves?

The body is divided into four plexus regions. The cervical plexus, brachial plexus, lumbar plexus, and sacral plexus.