If we ask ourselves what has been the starting point from which it has come to a nervous system as complex as mammals one? We must place ourselves in the annelids ladder-ganglionic system (see picture # 1), formed by a chain of node pairs, which begins in the cervical region and continues in ventral position to the end of the body (caudal completion). This formation is known colloquially as "rope ladder" because the node pairs are joined together by longitudinal and transverse fibers. Here it is important to consider that at some point in the cervico-caudal path this chain surrounds the esophagus forming the periesophageal necklace. This formation will later explain the chain transit to a position attached to the spine.

As described in the Disclosure blog (XXVII) entitled "Brainstem ganglia chain: the origin of the cranial pairs", the first 15 pairs are the source of the eyes (see also Disclosure XIII) and the central nervous system to Ehrenriter Andersch core. Here we can add that pairs 16 and 17 may be the source of the arqueocerebellum and the paleocerebellum respectively and consider the neocerebellum has its origin in a migration of brain cells.

There is no reason to think that the ladder-ganglionic system ended in these first 17 pairs. This, together with the fact that we still must add the spinal cord and that there is another anatomical structure that develops in a node pairs structure, makes reasonable to think that once the central nervous system was formed, grouped in the cervical region and heteronomically metameryzed (irregular metamers) , the chain extends in the caudal direction giving phylogenetic origin to the spinal cord and to the sympathetic and parasympathetic nervous system node chain.

There is a chain of cervical nodes that consitutes the anatomical basis of the autonomic nervous system and which disposition may seem confusing for being arranged between lymph nodes. This confusion has been the source of various classifications (John Langley 1898, Rouviere 1938, E.Rubin 1983, American Association of Cancer 1997, American Academy of Odontologists 1998, and another one based on the image).

As shown in the figure, we consider this chain is composed of three nodes (upper cervical, middle cervical and lower cervical) that would correspond to the locations 19, 20 and 21 of the annelids ladder-chain.

This chain is the anatomical basis of the autonomic nervous system and assumes various functions through 9 innervations coming out from it. The superior cervical ganglion (sympathetic) is responsible for homeostasis and innervates the eye and pineal gland, glands (lacrimal, submandibular, parotid) and the circulatory system, being responsible to react to heat stress situations.

The middle and lower cervical nodes, basically destined to heart rate control and to establish connections with the thoracic chain.
This chain and its continuation, the lumbar chain, will be the target of the next DISCLOSURE delivery XLVIII-2.