Ganglion chain of brainstem. Origin of craneal pairs. Disclosure 17.
The works of Antonio Scarpa (S.XVIII) Ludwig Edinger and Carl Westphal, Josep Erlanger and Herbert Gasser (S.XX) together with the ones of Ehrenritter and Andersch separately, allow to know part of the ganglion structure of brainstem.
This anatomic area placed just under the brain, over the etmoid and esphenoid bones, is highly important because of its origin of the central nervous system and its phylogenetic is important in the knowledge of motor, sensorial system and nerve supply to vital organs.
Traditionally, the XII pairs of cranial nerves have been considered as the origin of the anatomic structure of the brainstem. But several studies have distinguished between the apparent origin of these nerves (organs and muscles) and the real origin; it is the ganglion pairs of brainstem.
Recently, eyes and pituitary have been related to this pair of ganglions so it is not a chain of 12 pairs but larger, including eyes, pituitary, smell and traditional ganglion pairs that we can extend to brain, cerebellum and spinal cord and pairs of lymphatic ganglions constituting lumbo aortic chain.
This model would be based in one ancient one that can be found in annelids and known as “rope ladder” and that World be perfectly adapted to the bilateral symmetry of most modern animals.
The disposition is going to be explained step by step:
1) In webblog Disclosure 13 called, “the eye origin” we pointed about Tessmar-Raible and Snyman in 2004 isolated Light sensitive opsines in the cells of the marine annelid Platynereis dumerilii (living fossil of 600 years) with similar structure to the opsines existing in the rods and cones of vertebrate. In this way there is an established biochemical relation between the nervous system of marine annelids and the first cranial pair of the nervous system in the current vertebrates (the eyes). From this primitive system of annelids, insects and vertebrates have evolutions in independent ways so eyes and nervous systems are different. However, the model is identical: a primitive nervous ganglions that become specialized although maintaining connexion between them (rope ladder)
2) In webblog Disclosure 16, called “pituitary origin” , we pointed that the current pituitary is a gland place in the cranium base of complex anatomic structure whose primitive origin can be found in annelids existing in the cambric age, 500 million years ago. So, alter the eyes (the first ganglion pairs) we continue with pituitary as representative of the second ganglion pair.
3) In the current webblog we will follow the route through the following pairs of lymphatic ganglions evoluted to the ganglion pairs of brainstem, brain base and going to cranial nerves that after emerging though the holes of the cranial base are distributed around the head, neck, thorax and abdomen.
At this point we wonder about the order of them. It was shown that the first pair corresponds to the eyes one and the second to hypophisis.
4) Which is the third pair? Following the anatomic order the main probability is that they correspond to the ganglions from where olfactory nerves depart transmitting olfactory impulses and placed in olfactory foramen in the cribriform plate of ethmoid. This position will explain the progress towards the face so it will drag to the front and up the pairs IV, V and VI of ganglions (base for the later development of protobrain, deutrobrain and tritobrain, thanks to the intracranial space accessible from this position. (in front and behind). In this way the eye is connected with pituitary and the smell and the brain. This quadruple connexion opens the options to the outer influence on the reproductive cycle of animals.
Ganglion pairs from VII to XV are:
VII) Nucleous Edinger-Westphal or oculomotor. With motor functions it innervates the papelbral elevators superior, superior straight, media superior, straight inferior and oblique inferior, that make almost all ocular movements simultaneously and also innerves the sphincter of the pupil. The connexion between pair VII with the pair of the brain would explain the relationship between the ocular expression and the cerebral status. VIII) Núcleo troclear. Con funciones motoras inerva el músculo oblicuo superior y mantiene igualmente relation con el cerebro a través del (VI) par.
IX) Passer ganglion or trigemin. With sensitive and motor functions innerves the ophthalmic nerve, the maxillary nerve and mandibular nerve. It gets sensitive information from the FACE and innerves the mastication muscles.
X) Abducens nucleus. With motor functions innerves the lateral straight muscle of the eye.
XI) Facial nucleus or superior salivary. With motor, secretor and sensitive functions gets motor innervation to the muscles of face expression, posterior digastrics muscle and receives gustative impulses of the anterior two thirds of the tongue. Gives secretor-motor innervation to salivary glands (except the parotide one) and to the tear.
XII) Scarpa ganglion or vestibular nucleus. With sensitive functions, it allows the sounds, rotation and gravity perception ( essential for equilibrium and movement) The vestibular branch leads impulses to coordinate the equilibrium and coclear arm leads auditory impulses.
XIII) Nucleus ambiguus or inferior salivar. With sensitive and motor functions receives the gustative impulses of the posterior third part of the tongue, giving secreto-motor innervation to the parotid gland and motor innervation to the estilopharynx muscle.
XIV) Dorsal vagal nucleous. Its is a controller of organs, motor and sensitive, from it the vagus nerves (parasimpathetic fibers) that innerve abdominal viscera’s placed under the spleenic flexure such as almost all pharynx nerves, except the estilopharynx that allow to make sounds with the soft palate. It receives taste from epiglottis.
XV) Andersch and Ehrenritter ganglions. This pair are asymmetric, in one side at the beginning of the hypoglossal and in the other in the accessory cranial nerve, both with motor function. The hypoglossal nerve gives innervation to the tongue muscles and other lingual nerves related with swallowing and sounds articulation. The accessory cranial nerve, innerves the sternocleidomastoid and trapezius, repeats the same functions of the vagus.
In this way we can find the phylogenetic explanation of how the pairs of ganglions of the rope ladder of annelids have evoluted to pairs of ganglions in the current mammals, and are the origin of the sensitive and motor nervous system distributed in all the body. The ganglions corresponding to the cerebellum, spinal cord and ganglion lymphatic system will be object of other chapters of this disclosure blog.