The<unk>  contains postganglionic<unk>  fibers whose cell bodies are located in the superior cervical ganglion. Their axons ascend with the internal carotid artery as a plexus of nerves, the carotid plexus.<unk>  fibers innervating the eye separate from the carotid plexus within the cavernous sinus.  They run forward through the superior orbital fissure and merge with the long<unk>  nerves (branches of the nasociliary nerve) and the short<unk>  nerves (from the<unk>  ganglion).<unk>  fibers in the short<unk>  nerves pass through the<unk>  ganglion without forming synapses.
Preganglionic<unk>  fibers originate from neurons in the intermediolateral column of the thoracic spinal cord, at the level of T1 and T2.  They form synapses in the superior cervical ganglion. The ratio of incoming to outgoing fibers (the “convergence”) in this ganglion is approximately 100:1.<unk>  motor neurons in the spinal cord are controlled by supranuclear pathways that descend through the brainstem and spinal cord.  Interruption of the<unk>  chain at any level (from the brainstem to the<unk>  ganglion) will produce pupillary constriction (miosis) and eyelid droop (ptosis) – the classic signs of Horner's syndrome.<unk>  fibers from the superior cervical ganglion innervate blood vessels (vasoconstriction), sweat glands, and four eye muscles: the dilator pupillae, the superior tarsal muscle, the inferior tarsal muscle and the orbitalis.
The dilator pupillae dilates the pupil; its action is antagonistic to the sphincter pupillae.  Pupil size is therefore under the dual control of<unk>  and parasympathetic nerves.
The superior tarsal muscle elevated the upper eyelid.  The levator palpebrae superioris, which is innervated by a branch of the oculomotor nerve, also elevates the upper eyelid.  Eyelid elevation is therefore under both voluntary and involuntary  control.  Interruption of either pathway will result in eyelid droop (ptosis).
The other two eye muscles with<unk>  innervation (the inferior tarsal muscle and the orbitalis) are vestigial in humans.  They are variable and often incompletely developed.
Sympathetic root of ciliary ganglion
Trigeminal nerve nuclei
Vestibular nuclei
Cranial nerve nucleus
Dorsal root ganglion
Cochlear nuclei
Vestibulospinal tract
Dorsal nucleus of vagus nerve