Where do parasympathetic fibers become classified as post-ganglionic?

The classification of parasympathetic fibers as post-ganglionic occurs at the ciliary ganglion. In the autonomic nervous system, fibers are considered pre-ganglionic before they synapse with a second neuron, which typically takes place in a ganglion. The ciliary ganglion is a specific structure located in the orbit where pre-ganglionic parasympathetic fibers from the Edinger-Westphal (EW) nucleus synapse with post-ganglionic neurons.

Once the synapse occurs, the fibers that emerge from the ciliary ganglion are classified as post-ganglionic because they have completed the synaptic transmission process. These post-ganglionic fibers then innervate the structures involved in the eye, such as the iris sphincter muscle and the ciliary muscle, thus playing a critical role in controlling pupil constriction and accommodation.

Understanding the location of the ciliary ganglion and its function in the parasympathetic pathway is essential in ocular physiology, particularly in the context of how the eye responds to various stimuli and conditions.