Site of preganglionic nerve cells that elicit dilation of pupil?

• A. Lateral horn, T1 and T2
• B. Edinger Westphal nucleus
• C. Superior cervical ganglion
• D. Ciliary ganglion

Answer: (A)

Pupillary dilation is driven by the sympathetic nervous system. The preganglionic cell bodies are located in the intermediolateral cell column (lateral horn) of the spinal cord at the upper thoracic levels, typically T1–T2. These fibers exit the spinal cord, join the sympathetic chain, and ascend to the superior cervical ganglion where they synapse. The postganglionic fibers then travel with the internal carotid plexus to reach the dilator pupillae muscle, causing the pupil to dilate. The Edinger–Westphal nucleus is the parasympathetic origin for pupil constriction, the ciliary ganglion is a parasympathetic relay for constriction, and the superior cervical ganglion is postganglionic, not the site of preganglionic neurons.