Cold sores on the skin of the mouth occur when herpes simplex viruses that are dormant in neural ganglia become active and travel to the skin of the mouth. Which of the following is the mechanism by which these viruses travel from the ganglia (located within the head) to the skin of the mouth?

a. transport along nerve impulses that travel down the axons
b. anterograde axonal transport
c. retrograde axonal transport
d. travel of the viruses along neurofibrils