Part 43

Structure of Nerve Pathways

Most pathways which carry nerve impulses from their origin or inception to the organ in which they are finally expressed as action of some sort or translated into sensation or into stimuli which pass out reflexly over a connected neuron, are composed of more than one neuron. The neurons of a nerve pathway are arranged end to end with the axons all pointing in one general direction so that the nerve energy travels always in the same direction over the entire nerve path. Impulses are transferred from the first neuron in the chain to the second, and from second to third, etc., by contact of the telodendria of the one neuron with the dendrites or receptive processes of the next. Part of the nerve pathway may be within the central axis and part within the trunk of a peripheral nerve.

Several peripheral pathways for afferent impulses may be joined to an efferent pathway so as to complete reflex arcs and the efferent cell be under the controlling influence of some upper neuron coming down from the central axis with the power either to permit or to inhibit the reflex acts which would otherwise take place as a result of peripheral stimuli. Several such lower cells may be under the domination of one upper neuron.

In some instances the nutrition of ganglia or nerve trunks, or of parts of the central axis itself, is under the control of sympathetic neurons terminating in connection therewith, so that interruption of the normal action of the sympathetic neuron may be followed by effects manifested through some distant part of the cerebrospinal system. In the following pages we shall discuss nerve pathways with reference to the explanation of diseases caused by vertebral subluxation impinging nerves either by tension or constriction, and therefore our grouping of parts will differ somewhat from any anatomical or physiological grouping with another object in view.

Important Nerve Pathways

To brain: C 2, 3, or 4 to superior cervical ganglion by direct impingement, through internal carotid nerve to sympathetic plexuses following branch arteries from Circle of Willis. The blood-supply of the brain is under control of the cervical sympathetic and most brain lesions or diseases are due to vascular changes leading to anaemia, hyperaemia, inflammation, or hemorrhage.

To meninges: Loop between first and second cervical nerves to trunk ganglion of vagus and through meningeal branches of vagus (P), or by way of internal carotid nerve to pial sympathetic plexuses. (P) The connection of the first, second, or third cervical with cerebral meningitis is established clinically but there is still doubt as to the explanation.

Eye and Muscles, Retina, Optic Nerve: The external muscles of the eye, the four recti and two oblique with the levator palpebrae superioris, are innervated by the Oculomotor, or third cranial, and the fourth and sixth cranial, which receive branches from the cavernous plexus of the sympathetic derived from the internal carotid branch of the superior cervical ganglion. As the ganglion lies in front of the transverse processes of the second, third, and fourth cervical vertebrae, direct impingement upon it by subluxation of one of these vertebrae may cause strabismus or other affection of the external ocular muscles.

The eye-ball receives filaments from the ciliary or ophthalmic ganglion, which in turn is connected with the cervical ganglion by way of cavernous plexus and internal carotid nerve. This pathway controls the radial fibres of the iris and dilates the pupil as a part of the light accommodation reflex mechanism. Loss of pupillary reaction, especially with small pupils, suggests upper cervical subluxation.

The retina, containing the cells of origin of the optic nerve axons and being the special end-organ of the sense of sight has no direct spinal or sympathetic connections but its blood-supply, and therefore its nutrition, is influenced by branches from the sympathetic which enter with the central artery of the retina. Retinal hemorrhage has been cured by cervical adjustment, C 2, 3, or 4.

The conjunctiva is innervated by the sympathetic and by the fifth cranial, or trigeminal.

Olfactory Nerve: Nerve of smell, distributed to the Schneiderian membrane over the upper portion of the nasal septum and over the upper lateral wall. There is no known connection by which the trunk of the olfactory nerve can be reached by adjustment but the condition of the special end organs in the membrane and their ability to functionate depend not only upon the integrity of their axons but also upon the nutrition and moisture of the membrane in which they are embedded. This is under the control of the Vidian nerve and of branches from the spheno-palatine, or Meckel’s ganglion, both connected with the carotid plexus of the sympathetic and therefore responsive to adjustment of C 2, 3, or 4. This is also the route by which epistaxis is usually checked.

The external nasal muscles, like those of the rest of the face except some of the muscles of mastication, get their supply from the facial nerve, which connects with the sympathetic plexus on the middle meningeal artery. It may be said parenthetically here that peripheral facial paralysis (Bell’s palsy) yields to adjustment and proves the value of this connection. The nasal integument is under the sensor control of the trigeminal and trophic disturbances may result from its involvement.

Trigeminal Nerve: This is the great sensor nerve of the face and carries a motor division, the inferior maxillary, to some of the muscles of mastication, as the temporal, masseter, and buccinator. It has connected with it four ganglia, which also receive sympathetic roots, and the ganglion of origin of its sensor axons, the Gasserian or semilunar, also receives direct sympathetic communications. The importance of this communication is shown by the powerful effect of adjustment of third or fourth Cervical for tic dolouroux.

Ear: The external ear receives branches from the vagus and from the first and second cervical nerves. The middle ear and Eustachian tube are supplied by the tympanic plexus made up of branches from the glosso-pharyngeal, otic ganglion, facial nerve and the small deep petrosal from the sympathetic on the carotid artery. By all these routes communication from the third and fourth cervicals is possible but especially is the latter important. The fourth cervical is the especially frequent subluxation with middle ear disease. To the internal ear and auditory or acoustic nerve there appears to be no direct route from the spine. It has not yet been conclusively established within the writer’s knowledge that adjustments will affect auditory deafness but Meniere’s Disease, inflammation of the semicircular canals, has been cured repeatedly by adjustments of Atlas or Axis, by what route I am unable to state.

Teeth and Gums: It is probable that the only connection between the vertebrae and the teeth is an afferent one by way of the trigeminal. Toothache may be stopped by adjustment of C 3, or C 4, but no evidence is at hand to show that the condition of the teeth is improved or that more than a temporary effect can be had. Trophic changes in the gums may be due to vascular disturbances controlled by the sympathetic.

Tongue: The hypoglossal, motor nerve to both the intrinsic and extrinsic muscles of the tongue, receives direct axons from the loop between the first and second Cervical nerves. Sympathetic fibres pass to the blood-vessels and secreting glands of the tongue.

Tonsils: Receive fibres from the spheno-palatine ganglion and by this means are brought under the domination of C 2, 3, and 4. Abundant clinical evidence in tonsilitis, simple, follicular, and suppurative, proves this to be the practically, as well as anatomically, correct nerve connection.

Salivary Glands: The parotid receives branches from the great auricular nerve from the second and third cervical, and from the sympathetic on the external carotid artery, branches from the superior cervical ganglion. The submaxillary and sublingual glands are connected with the submaxillary ganglion, which receives a sympathetic root and which, with the chorda tympani also carrying fibres derived from the sympathetic, controls the secretions of these glands.

Pharynx: The pharyngeal plexus is a mixture of sensory axons from the glosso-pharyngeal, motor components from the vagus and probably sensor from the same nerve, and sympathetic branches from the superior cervical ganglion. All of these may be influenced by the upper cervical adjustment.

Larynx: According to anatomy the larynx is innervated by the superior and inferior, or recurrent, branches of the vagus and by sympathetic branches from the superior cervical ganglion. Clinically the sixth cervical adjustment cures laryngitis and aphonia. The explanation probably lies in the fact that the thyroid branches of the middle cervical ganglion, lying in front of the transverses of the sixth, communicate within the thyroid gland with the recurrent laryngeal and with the external laryngeal branch of the superior laryngeal.

Thyroid Gland: “The nerves to the thyroid are amyelinic and are derived from the middle and inferior ganglia of the sympathetic.” (Gray.) The middle cervical ganglia are situated in front of the transverse processes of the sixth cervical vertebra. Clinically, the sixth cervical reaches goitre.

Muscles of Neck: The platysma is supplied by the facial nerve; the sternomastoid by the spinal accessory and cervical plexus; the infrahyoid region by the first three cervical nerves; the suprahyoid region by the facial and the ansa cervicalis; the anterior and lateral vertebral muscles by the cervical nerves from second to seventh inclusive, but especially the second, third, and fourth. It will be seen that muscular disturbance in the neck may result from any cervical subluxation. Torticollis, which usually involves the sternomastoid, yields to the second cervical most frequently.

Lymph Nodes of Head and Face: These lymph nodes are controlled by the cervical sympathetic. Pathological changes in one or more nodes requires careful cervical palpation to determine the presence of a subluxation away from the affected side.

Muscles of Back: The trapezius is innervated by the spinal accessory and by the third and fourth cervical nerves; the latissimus dorsi by the sixth, seventh, and eighth cervical through the middle or long subscapular. Occasionally a tender nerve, traceable from the lower reaches of the latissimus to the cervical region has mislead the practitioner into imagining a cervical connection over the back with internal viscera.

The second layer of the back is supplied by the third, fourth, and fifth cervical nerves. The third layer is innervated by the middle and lower cervical and upper three thoracic nerves except the serratus posticus inferior which is supplied by the ninth, tenth, and eleventh thoracic. The fourth and fifth layer are supplied by the posterior primary divisions of the spinal nerves and any given section of these layers may be traced to a vertebra directly above, or cephalad.

Thoracic Walls: The parietal muscles of the thorax are innervated by the intercostal nerves and a very definite segmental association with the spine is traceable.

Diaphragm: Phrenic nerve, which arises from fourth cervical chiefly; lower intercostals, especially eighth and ninth; and phrenic plexus of the sympathetic which may sometimes be reached from the fourth or fifth dorsal vertebrae through the gangliated cord. For motor disturbances of the diaphragm adjust fourth cervical.