Epinephrine pen usage. 3d animation showing the auto-injector administration of adrenaline intramuscularly into the anterolateral aspect of the thigh. The adrenaline travels to the heart and lungs where beta receptors are stimulated, causing the circular muscles (brown) of the bronchus to relax. This allows the bronchial tubes to expand and the airways to widen. Epinephrine pens are used for self-administration as an immediate, emergency treatment for anaphylaxis (severe, life threatening allergic reactions).