Sympathetic ganglia are the ganglia of the sympathetic nervous system (see Figure 1, red fibers). They deliver information to the body about stress and impending danger, and are responsible for the familiar fight-or-flight response. This response is also known as the sympathetico-adrenal response because the pre-ganglionic sympathetic fibers that end in the adrenal medulla (but also all other sympathetic fibers) secrete acetylcholine, which activates the secretion of adrenaline (epinephrine) and to a lesser extent noradrenaline (norepinephrine) from it. Therefore, this response that acts primarily on the cardiovascular system is mediated directly via impulses transmitted through the sympathetic nervous system and indirectly via catecholamines secreted from the adrenal medulla.
An example of a sympathetic ganglion in a thoracic nerve is shown in Figure 2. Sympathetic ganglia contain approximately 20000–30000 nerve cell bodies and are located close to and on either side of the spinal cord in long chains (depicted as the string-of-pearls structure with many red lines in Figure 1). Sympathetic ganglia are the tissue from which neuroblastoma tumours arise.
The bilaterally symmetric sympathetic chain ganglia, also called the paravertebral ganglia, are located just ventral and lateral to the spinal cord. The chain extends from the upper neck down to the coccyx, forming the unpaired coccygeal ganglion. Preganglionic nerves from the spinal cord synapse at one end of the chain ganglia and the postganglionic fibre extends to an effector, typically a visceral organ in the thoracic cavity. There are usually 21 or 23 pairs of these ganglia: 3 in the cervical region, 12 in the thoracic region, 4 in the lumbar region, 4 in the sacral region and a single, unpaired ganglion lying in front of the coccyx called the 'Ganglion impar'.
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. The sympathetic nervous system is said to have "thoracolumbar outflow" based on its location.