Anatomy study note · Head and neck

Iris

A thin, pigmented contractile diaphragm with a central aperture, the pupil, lying in the aqueous humour between the cornea and lens and dividing the anterior from the posterior chamber.

Key points

• Sphincter pupillae = parasympathetic (III) → constricts.
• Dilator pupillae = sympathetic → dilates.
• Light reflex via pretectal nuclei (direct + consensual).
• Sphincter + dilator pupillae: ectoderm (optic cup).
• Coloboma: choroidal fissure fails to close.
• Dilator: sympathetic. Sphincter: parasympathetic (III).

The full note in the atlas also covers

Features · Action · Nerve supply · Histology · Development · Clinical notes

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Written from

• Snell’s Clinical Anatomy by Regions, 10th ed., ch. 12, PDF pp. 1597–1598, 1602–1603
• Inderbir Singh’s Human Embryology, ch. 7, PDF p. 110; ch. 19, PDF pp. 356–360
• BRS Cell Biology & Histology, 7th ed., ch. 21, PDF p. 382

More from the head and neck

• Lacrimal apparatus
• Laryngeal membranes and ligaments
• Larynx
• Lateral cricoarytenoid
• Lateral pterygoid
• Lateral rectus
• Lens
• Levator palpebrae superioris
• Levator veli palatini
• Lips and oral cavity
• Longus colli and longus capitis
• Mandible

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