A light will act as a stimulus. This will trigger the photoreceptors and a signal will be conveyed to the ganglion cells. Their impulse will send through the axons in a similar manner as those carrying information to the optic never head.
However, these information from the ganglion cell passes information to the superior colliculus through the brachium where they synapase on the pretectal olivary nuclei. After the projection to the pretactactal nucleus, these projections will lead to the edinger westphal nucleus by internuncial neurons.
The picture gives an illustration of how the signal is sent.
Efferent limb of the parasympathetic pathway:
After getting the information from the pretactal nucleus, Edinger Westphal nucleus will then send information through fibers to join the oculomotor cranial nerve VIII(8) and follow the course on the dorsomedial surface of the nerve. These fibers will then emerge to enter the orbit with the inferior obliquw branch of cranial nerve III (3) by crossing through the cavernous sinus. The synapses at the ciliary ganglion enter through the short posterior ciliary nerves to distribute fibers to the ciliary body and iris.
The above picture shows the innervation of the cilary muscle from the sideways.
http://www.tedmontgomery.com/the_eye/eyephotos/reflex.html
(Open this link)
As seen in this website, The nerve impulse travels to the pretactal nucleus then to the edinger westphal nucleus.
Efferent sympathetic pathway: It was believe to start in the hypothalamus. It is projected in straight synapses. These neurons project to and synapse upon intermediolateral cell column from the C8-T2 spinal cord. The neurons exit through the superior cervical ganglion. The fibers passes through the internal carotid artery, which enter the cavernous sinus and travel with cranial nerve VI in the cavernous sinus to enter the superior orbital fissure with cranial nerve V.
Next, the fibers will travel with the nasociliary branch of V, and pass through the ciliary ganglion without synapsing. Finally, the fibers pass through the long ciliary nerves to terminate on the dilator muscle.
Source from: http://www.medrounds.org/ocular-pathology-study-guide/2005/11/pupillary-reflex-pathway.html
