lateral horn of grey and emerge via the ventral root. They enter their respective spinal nerve (e.g. T5), and thus enter the white ramus communicans. This myelinated division can then enter the sympathetic chain. Here four options are available to the fibers: (1) they can run up the chain and synapse, (2) they can synapse at the level of entry, (3) they can pass straight through and synapse elsewhere – such as in the case of T5–12 (the splanchnic nerves), or (4) they can enter the chain and descend to synapse. It is this ability to move superiorly and inferiorly along the chain that results in the mass response to the sympathetic nervous system. A preganglionic fibre may synapse to 15–20 postganglionic fibres. The postganglionic neurons extend across most of the body. Upon exiting the sympathetic chain, the fibres enter a less-myelinated gray ramus communicans. There is still a myelin sheath present – just in far lower amounts compared to the white ramus communicans. This ramus then enters the spinal nerve and is sent to its synapsing target, or becomes a visceral branch to enter a plexus (e.g. the superficial or deep cardiac plexuses), or synapses directly onto a target. Collateral ganglia Neurons of the collateral ganglia, also called the prevertebral ganglia, receive input from the splanchnic nerves and innervate organs of the abdominal and pelvic region. These include the celiac ganglia, superior mesenteric ganglia, and inferior mesenteric ganglia. Additional images References External links () Sympathetic nervous system