Description

Figure 1 illustrates the subdivision of the nervous system with particular reference to the parasympathetic nervous system and the structures related to the eye which are innervated by it.

A diagram of the parasympathetic nervous system is shown in Figure 2. Its outflow stems from both cranial and sacral regions. As far as the eye is concerned the parasympathetic nerve supply to the iris sphincter muscle and ciliary muscle originates in the third nerve nucleus (Edinger Westphal) in the central nervous system. It leaves the central nervous system via the third cranial nerve (oculomotor). This long preganglionic nerve synapses with the ciliary ganglion. Short postganglionic nerves leave the ganglion to innervate the sphincter pupillae muscle of the iris and the ciliary muscle. The lacrimal glands also receive parasympathetic nerves which flow from the seventh nerve nucleus and pass to the glands via the sphenopalatine ganglion.