How does the lacrimal reflex cause tears when the eye is irritated?

The lacrimal reflex is an emergency response triggered by irritants to the cornea, conjunctiva, or nasal mucosa, as well as other stimuli like bright light or certain tastes.1

The process functions through a specific neural pathway:

• Afferent (Sensory) Pathway: When the eye is irritated, sensory nerve endings are stimulated. These signals travel to the brain via the trigeminal nerve.1
• Motor (Involuntary) Pathway: The brain responds via the autonomic division of the nervous system. The facial nerve provides the dominant parasympathetic motor influence, signaling the lacrimal gland to produce an abundant secretion of tears to flush away the irritant.1

This reflex is distinct from "psychical weeping" (emotional tears) and can be inhibited by paralyzing the sensory nerve endings with substances like cocaine or by blocking the parasympathetic response with atropine. During such copious secretion, a drainage mechanism known as the lacrimal pump—driven by the contraction of the orbicularis muscle during blinking—helps manage the excess fluid.1