![]() Evidence suggests these pupillomotor ganglion cells are melanopsin-containing, and have some intrinsic ability to respond to light on their own, in addition to input from the photoreceptors. There is a specialized subset of retinal ganglion cells that send their output directly to the pupillary centers in the midbrain. The response of the photoreceptors to a light stimulus is processed in the retina and conveyed to the brain by the retinal ganglion cell axons. Many more postganglionic axons innervate the ciliary muscle than the pupillary sphincter (ratio of 30:1) this fact is important in the discussion of Adie tonic pupil later in this chapter. ![]() The ciliary ganglion is the origin of axons that enter the posterior aspect of the globe as the short posterior ciliary nerves, traveling in the suprachoroidal space to innervate both the pupillary sphincter (for pupillary constriction) and the ciliary muscle within the ciliary body (for accommodation). The motor root is short because the ciliary ganglion lies close to the inferior division of CN III and adjacent to the inferior rectus muscle. As the inferior division courses along the lateral border of the inferior rectus, the parasympathetic fibers exit midway as the motor root of the ciliary ganglion, to synapse in the ciliary ganglion ( Figure 11–3). The parasympathetic pupillary axons travel in the inferior division of the oculomotor nerve, along with fibers innervating the inferior oblique muscle. CN III traverses the cavernous sinus, entering the orbit through the superior orbital fissure where the nerve bifurcates. The pupillary fibers occupy a superficial position in the nerve and are more vulnerable to external compression of CN III (eg, aneurysm or uncal herniation). As described in Chapter 9, this nerve has a short but eventful course in the subarachnoid space, passing between the superior cerebellar and posterior cerebral arteries to travel both adjacent and parallel to the posterior communicating artery (see Figure 9–11B). Fascicles from this parasympathetic motor nucleus join other fascicles from the CN III nuclear complex and traverse the midbrain tegmentum, exiting the brainstem at the interpeduncular cistern to form CN III. Parasympathetic pupillomotor fibers originate from the midline but paired Edinger-Westphal nuclei, which occupy the most dorsal position in the CN III nuclear complex. The pupillary constrictor muscle is innervated by the parasympathetic component of CN III. Therefore, asymmetric facial flushing and sweating are important accompanying clinical signs with localizing value. ![]() From the superior cervical ganglion, most third-order (post-ganglionic) axons travel with the internal carotid artery through the cavernous sinus and eventually to the eye, with the remainder following the external carotid to supply vasomotor and sudomotor (sweat gland) innervation to the face. These second-order axons pass through the stellate ganglion and ascend to synapse in the superior cervical ganglion located at the carotid bifurcation, at the level of C3/C4 and the angle of the jaw. Axons from these second-order (preganglionic) neurons then exit the spinal column primarily at the Tl level in the chest cavity, arch over the apex of the lung, and travel under the subclavian artery (ansa subclavia) to ascend with the cervical sympathetic plexus associated with the carotid arteries. These axons synapse at the ciliospinal center (of Budge) located at the C8 to T2 level in the spinal cord ( Figure 11–2). The oculosympathetic chain begins with first-order neurons located in the posterolateral hypothalamus, with axons that descend through the brainstem and into the intermediolateral cell column of the spinal cord.
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