Light reflex is carried through: March 2005

Ans. D: Cranial nerve II The optic nerve is responsible for the afferent limb of the light reflex - it senses the incoming light. The oculomotor nerve is responsible for the efferent limb of the light reflex - it drives the muscles that constrict the pupil. Neuron 1: The light reflex pathway begins with retinal ganglion cells, which convey information from photoreceptors to the optic nerve ( the optic disc). The optic nerve connects to the pretectal nucleus of the upper midbrain, bypassing the lateral geniculate nucleus and the primary visual coex. Neuron 2: From the pretectal nucleus, axons connect to neurons in the Edinger-Westphal nucleus, whose axons run along both the left and right oculomotor nerves. Neuron 3: Oculomotor nerve axons synapse on ciliary ganglion neurons. Neuron 4: Neuron 4 innervates the constrictor muscle of the iris