What nerve controls the direct pupillary light reflex?
The optic nerve
The optic nerve, or more precisely, the photosensitive ganglion cells through the retinohypothalamic tract, is responsible for the afferent limb of the pupillary reflex; it senses the incoming light.
What happens during direct light reflex?
The reflex is consensual: Normally light that is directed in one eye produces pupil constriction in both eyes. The direct response is the change in pupil size in the eye to which the light is directed (e.g., if the light is shone in the right eye, the right pupil constricts).
What is the pathway for light reflex?
Pathway: Afferent pupillary fibers start at the retinal ganglion cell layer and then travel through the optic nerve, optic chiasm, and optic tract, join the brachium of the superior colliculus, and travel to the pretectal area of the midbrain, which sends fibers bilaterally to the efferent Edinger-Westphal nuclei of …
What nerve controls the pupil dilation?
Oculomotor nerve (III) is responsible for the control of the pupil (constriction) via parasympathetic fibres (this is opposed by dilator tone controlled by sympathetic pathways).
What causes afferent pupillary defect?
Retinal Causes of a Relative Afferent Pupillary Defect Ischemic retinal disease: Causes include ischemic central retinal vein occlusion, central retinal artery occlusion, severe ischemic branch retinal or arterial occlusions, severe ischemic diabetic or sickle-cell retinopathy.
What is afferent pupillary defect?
Background. Relative Afferent Pupillary Defect (RAPD) is a condition in which pupils respond differently to light stimuli shone in one eye at a time due to unilateral or asymmetrical disease of the retina or optic nerve (only optic nerve disease occurs in front of the lateral geniculate body).
Which nerves are mostly involved in pupil dilation?
The iris dilator muscle is controlled by the sympathetic nervous system, the part of the autonomic nervous system that is involved in arousal, wakefulness, and the fight-or-flight response; the link between pupil dilation and the sympathetic nervous system explains why pupils are relatively large when someone is …
What nerves are involved in pupil dilation?
What is the Abducens nerve responsible for?
extraocular motor functions
Cranial nerve six (CN VI), also known as the abducens nerve, is one of the nerves responsible for the extraocular motor functions of the eye, along with the oculomotor nerve (CN III) and the trochlear nerve (CN IV).
What sympathetic nerve dilates the pupil?
The pathway of pupillary constriction begins at the Edinger-Westphal nucleus near the occulomotor nerve nucleus. The fibers enter the orbit with CNIII nerve fibers and ultimately synapse at the cilliary ganglion. Sympathetic innervation leads to pupillary dilation.
Do the parasympathetic or sympathetic nerves trigger pupil constriction?
Stimulation of the autonomic nervous system’s sympathetic branch, known for triggering “fight or flight” responses when the body is under stress, induces pupil dilation. Whereas stimulation of the parasympathetic system, known for “rest and digest” functions, causes constriction.
Which cranial nerves were involved in the afferent and efferent limb of this reflex?
The afferent limb of the reflex is supplied by the glossopharyngeal nerve (cranial nerve IX), which inputs to the nucleus solitarius and the spinal trigeminal nucleus. The efferent limb is supplied by the vagus nerve (cranial nerve X) from the nucleus ambiguus. All of these are located in the medulla.
Is abducens nerve sensory or motor?
motor nerves
The trochlear, abducens, accessory, and hypoglossal nerves are only motor nerves; the trigeminal nerve is both sensory and motor; the oculomotor nerve is both motor and parasympathetic; the facial glossopharyngeal, and vagus nerves have sensory, motor, and parasympathetic components (Standring, 2008).
Which neural segments are involved in the left direct light reflex?
Left direct light reflex involves neural segments 1, 5, and 7. Segment 1 is the afferent limb, which includes the retina and optic nerve. Segments 5 and 7 form the efferent limb. Left consensual light reflex involves neural segments 2, 4, and 7.
What is the afferent limb of the pupillary light reflex neural pathway?
The pupillary light reflex neural pathway on each side has an afferent limb and two efferent limbs. The afferent limb has nerve fibers running within the optic nerve ( CN II ). Each efferent limb has nerve fibers running along the oculomotor nerve ( CN III ).
What is the difference between direct and consensual light reflexes?
Direct light reflex of right pupil involves the right optic nerve and right oculomotor nerve, which are both intact. The left consensual reflex is intact. Consensual light reflex of left pupil involves the right optic nerve and left oculomotor nerve, which are both undamaged. The left direct reflex is lost.
What nerve controls the pupillary light reflex?
Pupillary light reflexes require both optic and oculomotor nerve (cranial nerve III) to constrict pupils upon light exposure. The optic nerve mediates the afferent limb of the pupillary reflex, whereas the oculomotor nerve involves the efferent limb of the reflex.