1. An action potential moves down the axon and arrive at a varicosity

2. Depolarisation at the varicosity activating voltage gated Ca2+ channels

3. Ingress of calcium causes release of neurotransmitters - mainly noradrenaline

4. NA diffuses to the vascular smooth muscle cells where it binds mainly α1 – contraction; some α2 – contraction and β2 – relaxation. Modulation of responses in both constriction and dilatation

5. The noradrenaline is then taken up again and recycled or broken down

6. Adrenaline from the adrenals and released into the circulation can also act at α1 or β2 receptors

Review: Nervous & hormonal control of vascular tone (Physiology)