Human Anatomy

Discuss the roles of sodium, calcium and potassium ions in an generation of an action potential.
An action potential need to be generated prior to the synaptic communication between neuron cells. How will you explain what an action potential is to a 6 year child.
Physically, marathon runners and body-builders look distinctively different. Discuss in detail how the training regiments of the afore-mentioned athletes affects the difference in the types of muscles fibers they have.