Also attached to the follicle is a tiny bundle of muscle fiber, called the "arrector pili", which is responsible for causing the follicle lissis to become more upright the surface of the skin. The muscle area can also cause the follicle to stick up slightly above the nearby skin (piloerection) with a pore incased with skin oil. This process results in goose bumps (or goose flesh). Stem cells are at the junction of the arrector and the follicle, and are principally responsible for the ongoing hair production during a process known as the Anagen stage.