Dorsal root ganglion neurons differentiate from neural crest progenitors. The preganglionic parasympathetic axons of this nerve synapse in the pterygopalatine ganglion. The axons of dorsal root ganglion neurons are known as afferents. Lumbar splanchnic nerves provide sympathetic innervation via the inferior mesenteric ganglion. This communicating branch carries postganglionic parasympathetic axons from the pterygopalatine ganglion. The axons of ganglion cells form the two optic nerves. Specifically, BDNF promotes survival of dorsal root ganglion neurons. Postsynaptic fibers from the ciliary ganglion form the short ciliary nerves. The pineal gland receives a sympathetic innervation from the superior cervical ganglion. There is a brain, a subesophageal ganglion, three thoracic ganglia, and six abdominal ganglia. VZV then remains latent in the dorsal ganglion cells of the sensory nerves. It receives sympathetic innervation from the celiac ganglion. Diseases of the ciliary ganglion produce a tonic pupil. The low frequency drop-off is due to lateral inhibition within the retinal ganglion cells. These colours roughly correspond to the sensitivities of the retinal ganglion cells.