What is a functionally specialized region of a cell membrane, typically characterized by the presence of specific proteins, called?

Membrane domain

Explanation:

Membrane domains are regions of the plasma membrane that have a specific functional specialization. They arise from movement restriction of the components of the membrane.  If we examine the detail of the structure of many transmembrane proteins, we see that they often possess three different domains, two hydrophilic and one hydrophobic.

Since these transmembrane domains "anchor" the protein to the lipid bilayer, these proteins do not float freely and cannot be isolated without first dissolving the lipid bilayer with detergents.

option a is correct i.e.

explanation:

in context to the membrane of nerve impulse, the outer membrane of neuron is semi permeable that is only sodium ions can pass through the membrane i.e. smaller ions can pass through the membrane while larger ions cannot pass through it.