All parts of the brain › Functions › Eye reflexes (pupil and blink)

What part of the brain controls the pupil and blink reflexes?

Two short loops in the brainstem: light narrows both pupils through the midbrain, and a touch on the cornea closes both eyelids through the pons. [1][2][3][4]

The 3D brain needs JavaScript. The list of parts still says what each one does for the pupil and blink reflexes.

Not lit: the trigeminal nerve and facial nerve (not a shape in this model). Lit: whole parts; region borders not drawn.

Slice

All 7 parts are lit together. Drag to turn, pinch or scroll to zoom, tap a part on the brain or a name in the list to focus it; .

For the pupil, light on the retina travels along the optic nerve and optic tract to the pretectal area at the top of the midbrain, which signals the Edinger–Westphal nuclei on both sides; their parasympathetic fibres run out in the oculomotor nerve, relay in the ciliary ganglion and tighten the iris sphincter. For the blink (corneal) reflex, the trigeminal nerve senses the touch and the facial nerve closes the eyelids in about a tenth of a second. [1][2][3][4]

Not lit: the trigeminal nerve that feels the cornea, the facial nerve that closes the eyelids, and the ciliary ganglion, the relay behind the eye on the pupil’s path. Each is not a separate shape in this site’s 3D model (built from BodyParts3D 4.0), so no marker is placed at a guessed position; each nerve’s page lights where it leaves the brainstem. [4][1][5] See the trigeminal nerve (V), the facial nerve (VII).

The pretectal area is a region on the midbrain, not a separate shape. The 3D model has no shape for it, so the whole midbrain is lit; the region’s exact border is not drawn.

The Edinger–Westphal nucleus is a region on the midbrain, not a separate shape. The 3D model has no shape for it, so the whole midbrain is lit; the region’s exact border is not drawn.

Eye reflexes (pupil and blink): 7 parts lit

Eyeball, optic nerve, optic chiasm, optic tract, midbrain, oculomotor nerve and pons. Tap one to see where it is and what it does.

The parts and their roles

Both reflexes start and end here: light-sensitive retinal ganglion cells start the pupil reflex, and the iris sphincter that narrows the pupil sits in the front of the eye; a touch on its clear front, the cornea, starts the blink. [1][4] Where is the eyeball?
The incoming (afferent) limb of the pupil reflex: the retinal ganglion cell fibres run in the optic nerve (cranial nerve II) toward the pretectal nucleus. [1] Where is the optic nerve?
Where the fibres from the inner (nasal) half of each retina cross to the other side, so each optic tract carries signals from both eyes on to the pretectal area. [6] Where is the optic chiasm?
Most of its fibres go to the lateral geniculate body for seeing; smaller branches leave for the pretectal area of the midbrain, which controls the pupil’s response to light, and for the superior colliculus. [7][2] Where is the optic tract?
Holds both relays of the pupil reflex: the pretectal area near its junction with the forebrain, just in front of the superior colliculus, and the Edinger–Westphal nucleus beside the cerebral aqueduct, which starts the parasympathetic signal that narrows the pupil and focuses the lens. [2][3] Where is the midbrain?
The outgoing (efferent) limb of the pupil reflex: parasympathetic fibres from the Edinger–Westphal nucleus run along the outside of the nerve to the ciliary ganglion, whose fibres reach the pupil’s sphincter. It also lifts the upper eyelid through the levator palpebrae, the muscle that opens the eye after a blink. This atlas draws only its end branches in the eye socket. [1][8] Where is the oculomotor nerve?
Wikipedia’s Corneal reflex article places the reflex’s centre in the pons: the trigeminal signal from the cornea reaches it and the facial nerve, which leaves the brainstem at the lower edge of the pons, carries the command to close the eyelids. [4][9] Where is the pons?

Named areas on the lit gyri

The pretectal area, on the : A group of seven nuclei where the midbrain meets the forebrain, in front of the superior colliculus and behind the thalamus. Its olivary and posterior pretectal nuclei mediate the pupil’s narrowing to light; they grow more active as light gets brighter and signal the Edinger–Westphal nuclei. Other pretectal nuclei help the eyes follow moving things and keep them in focus. [2]
The Edinger–Westphal nucleus, on the : One of the two nuclei of the oculomotor nerve, at the level of the superior colliculus and beside the cerebral aqueduct; its parasympathetic neurons drive the iris sphincter (the pupil) and the ciliary muscle (focusing). [3]

How they work together

Light in one eye narrows both pupils: the pretectal nucleus sends fibres to the Edinger–Westphal nuclei on both sides, so the lit eye’s pupil narrows (the direct response) and so does the other (the consensual response). The pupil narrows about three times faster than it widens again. [1]
Fibres from the pretectal area to the Edinger–Westphal nucleus of the other side cross in the posterior commissure, just above the cerebral aqueduct. [10]
The blink has more than one trigger: touch on the cornea, eyelashes, eyelid skin or eyebrow; a sudden bright light (the dazzle reflex); or something coming fast at the eye (the menace reflex). Adults blink about 17 times a minute in a laboratory, fewer when reading, and a blink lasts on average 100–150 ms. The orbicularis oculi closes the eye through the facial nerve; the levator palpebrae opens it through the oculomotor nerve. [8]
Touching one cornea normally closes both eyelids (the direct and consensual responses of the corneal reflex), within about a tenth of a second. [4]
Honest limit: the pretectal area and the Edinger–Westphal nucleus are not separate shapes in this atlas (BodyParts3D 4.0 has no part for either), so the whole midbrain is lit for them; the blink centre is lit as the whole pons, and the oculomotor nerve lights only its branches inside the eye socket, not its course from the midbrain. [2][3][4][5]

The pretectal area also helps the eyes follow moving things, and the oculomotor nerve that carries the pupil signal also moves four of the six eye muscles. [2][11] What part of the brain controls eye movements?

Most optic tract fibres go on to the lateral geniculate body and the visual cortex for seeing; the pupil reflex takes only a side branch. [7] What part of the brain controls vision?

Sources

Facts describe anatomy and normal function only. A part lit here takes part in the pupil and blink reflexes; it does not do it alone, and it does other jobs too. The 3D model is the adult male BodyParts3D brain (credits and licence); on it the brainstem includes the midbrain, pons and medulla, so lighting the brainstem lights all three.