Ion channels are specialized proteins in the plasma membrane that provide a passageway through which charged ions can cross the plasma membrane down their electrochemical gradient.
Explanation:
Ion channels are molecular machines that serve as principal integrating and regulatory devices for controlling cellular excitability. Different types of ion channels have been described: channels that respond to mechanical, electrical (voltage-dependent ion channels), or chemical stimuli (ligand-gated ion channels); ion channels that are controlled by phosphorylation/dephosphorylation mechanisms; and ion channels that are dependent on G proteins. Most ion channels are of the voltage-dependent type and consist mainly of sodium (Na+), potassium (K+), and calcium (Ca2+) channels. Drugs can affect ion channel function directly by binding to the channel protein and altering its function or indirectly through G proteins and other intermediates. Lidocaine is a good example of a drug that directly affects voltage-gated Na+ channels by blocking the channel and thus Na+ entry into the cell.
both c and d are pretty accurate, but i dont have very much knowledge on warblers specifically. but those 2 answers would be the most common for such a case
