Ciliary ganglion and sphincter pupillae
Cortex & pupil · Tonic pupil
Preganglionic fibres leave the inferior division of CN III in the orbit (with the branch to inferior oblique) and synapse in the ciliary ganglion, which lies lateral to the optic nerve. Postganglionic fibres reach the sphincter pupillae and ciliary muscle in the short ciliary nerves, forming the efferent limb of both the light and near reflexes.
Traced from the start
Detail
- Ganglion roots
- Parasympathetic from CN III (synapses); sympathetic from the internal carotid plexus and sensory from the nasociliary nerve (both pass through)
- Effectors
- Sphincter pupillae (miosis) and ciliary muscle (accommodation) via muscarinic M3 receptors
- Antagonist
- Dilator pupillae via the sympathetic chain: hypothalamus to T1, superior cervical ganglion, carotid plexus
- Pharmacology
- Pilocarpine constricts; atropine and tropicamide dilate by muscarinic blockade
When it goes wrong
Postganglionic denervation of the ciliary ganglion (Holmes-Adie tonic pupil), typically a young woman
Unilateral dilated pupil that constricts sluggishly to light but better to near, with supersensitive constriction to 0.125% pilocarpine; ankle reflexes may be absent
Muscarinic blockade of the sphincter (atropine drops, anticholinergic plant exposure)
Fixed dilated pupil that fails to constrict even to 1% pilocarpine, which separates it from a third-nerve palsy
Interruption of the sympathetic supply to dilator pupillae (Horner syndrome)
Small pupil with partial ptosis and anhidrosis, the anisocoria greater in the dark, the reverse of a parasympathetic lesion
Practise this structure
1 question in the bank tagged Autonomic.