The lacrimation reflex is stimulated by irritation of the eye's conjunctiva and cornea, which increases tear volume. Afferent nerves in the ophthalmic and infraorbital nerves carry impulses to the brainstem and spinal cord. Efferent parasympathetic nerves from the pterygopalatine ganglion and sympathetic nerves from the upper thoracic spinal cord then activate the lacrimal and accessory glands to secrete the aqueous layer of tears, while tarsal and goblet cells produce the lipid and mucus layers.

9. The lacrimation reflex
• stimulated by irritation of the conjunctiva and
cornea, which elicits a large increase in tear
volume.
• afferent limb involves branches of the
ophthalmic nerve, with an additional
contribution from the infraorbital nerve if the
conjunctiva of the lower eyelid is involved

10. • Impulses enter the brain and spread by
interneurones to activate parasympathetic
neurones in the superior salivatory nucleus
(associated with the facial nerve) and
sympathetic neurones in the upper thoracic
spinal cord.

11. The efferent pathway
• the greater petrosal nerve[preganglionic
parasympathetic secretomotor fibres]
• the deep petrosal nerve[postganglionic
sympathetic fibres]
• the parasympathetic fibres relay in the
pterygopalatine ganglion
• sympathetic fibres pass through the ganglion
without synapsing.

12. Lacrimation reflex

13. The aqueous component (consisting primarily of proteins, ions and water) is
produced by the main and accessory lacrimal glands. Tarsal glands in the
eyelids produce the lipid layer of the tear film and the mucous component is
derived from conjunctival goblet cells.