Tutorial 3
Sympathetic Nerves
Sympathetic nerves control the iris dilator muscle, causing the pupil to dilate, and the blood vessels.
Pre-ganglionic nerves arise in the upper thoracic spinal cord and travel upwards in the sympathetic chain synapsing in the middle and superior cervical ganglia. Postganglionic nerves form a plexus on the internal carotid arteries (carotid plexus) and from there supply the radial muscle of the pupil. Acetylcholine is the pre-ganglionic neurotransmitter and noradrenaline the postganglionic transmitter acting at alpha-adrenoceptors causing radial muscle cells to contract and the pupil to dilate.
