APPPLIED KINESIOLOGY AND CHIROPRACTIC

A BRIEF DISCUSSION OF CRANIAL MANIPULATION AND VISCERAL AND SOMATIC RESPONSE

RICHARD BELLI, D.C.

For years clinicians have observed marvelous results from cranial bone manipulation, but along with these observations have come a great deal of conjecture and debate as to the mechanism. This discussion covers some of the plausible neurological mechanisms for these observations. These mechanisms include tonic labyrinthine reflexes, dural innervation, postural modulation by vestibulospinal projections, and vestibular projections to the reticular formation, thalamus, and hypothalamus.

The most striking observation of cranial manipulation is the diversity of physiological and therapeutic response. For decades clinicians have observed resolution of everything from low back pain to tachycardia. These observations, because they are so diverse have given cranial manipulation an almost mystical connotation, how else could such diverse responses be explained?

The debate has raged amongst anatomist and clinicians as to whether cranial bones do in fact move or if the sutures are fused making the cranium an immovable vault. It has been well documented by Upledger that there is a cranial respiratory mechanism. Many anatomist and clinicians claim that the cranium in vivo is wet and flexible, thus allowing for movement. This all leaves us with a preponerence of evidence that the cranium in vivo is an alive and movable mechanism.

The aforementioned leads us to the discussion as to what mechanically happens when the cranium is manipulated. Keeping it simple, and without getting into specific techniques, we assume that cranial techniques generally restore normal juxtapositional relationships and movement to the cranial respiratory mechanism. By restoring normal motion and function, one would assume that there is a change in the dura, or better said in dural tension, as well as a normalization of the bilateral temporal bone relationship. As discussed by Walther, Upledger, and others, the cranium is believed to function as a closed kinematic chain, in other words you can not affect a bone as a single entity, manipulation of one bone will affect all of them.

The dura is supratentorially innervated by the trigeminal nerve and infratentorially by the vagus nerve. This makes it enticing for cranial practitioners believe that cranial manipulation may have it therapeutic responses via the afferents of these nerves. Another school of practitioners finds it irresistible to believe that changes in cranial motion and normalizing of the flow of cerebrospinal fluids leads to therapeutic changes. And finally, some practitioners believe that normalization of the temporal bone relationship to each other accounts for the therapeutic effect.

Lets now look at these suspected mechanisms and determine which can explain the spectrum of clinical change. Logic would tell us that the modality that encompasses the neurological pathways that explain the broad spectrum of clinical change would be our prime candidate. Looking at the dura we have to take into consideration the sensory innervation and such aspects as dural tension. As previously mentioned the dura is innervated supratentorially by the trigeminal nerve and infratentorially by the vagus nerve. When the vagus and trigeminal nerves are brought to threshold by some sort of mechanical pressure the axons project to the sensory nuclei of each one of these nerves These include the sensory nucleus for the trigeminal nerve and the solitary nucleus for the vagus nerve. In theory the vagal and trigeminal afferent input will facilitate via collateral's the motor nuclei for the reticular formation and other bulbar nuclei facilitating visceral and somatic efferents. This in theory can account for visceral changes seen with cranial manipulation. The question at hand is whether the amount of movement that the cranial manipulation imparts is enough to bring the sensory aspects of the dura to threshold? Also we must consider that the majority of these afferents are nociceptive in nature. As Upledger describes there is a great deal of movement in the cranial sacral respiratory mechanism. If this movement is not enough to bring these afferents to threshold it is not likely that cranial manipulation will. However, this constant motion of the cranial sacral mechanism may be enough to maintain a base line level of mechanoreceptor barrage from the dura. If this is the case, then in theory, if there is a change in cranial sacral motion then the afferent barrage from the dura to the sensory nuclei of the trigeminal nerve and the solitary nucleus of the vagus nerve would change. In other words, a normal amount of cranial sacral motion will maintain a normal amount of afferent input to vital centers.

Looking at cerebral spinal fluid flow as a candidate one must question the actual changes that take place in pressure from normal abdominal and thoracic cavity pressure changes. The CSF pressure ranges from 50 to 150 mmHg. Keeping this in mind it is not likely that the subtle changes that are made with cranial manipulation are going to have a significant effect on the overall pressures.

The vestibular system is of primary importance in maintaining upright posture, muscle tone and eye movement. The two vestibular apparati do not function properly unless they are in normal juxtaposition with each other. If their positional relationship is lost, the vestibular output is of two different messages, which makes accurate central processing impossible. The central pathways of the vestibular system are principally motor reflex connections to nuclei innervating extraocular muscles, the motor reticular formation, the spinal motor neurons, and the cerebellum. With this in mind one can see there is an enormous amount of potential for affecting physiological function. The vestibular projections to the motor reticular formation are multipurpose purpose in nature. When you consider that blood pressure needs to change with position and muscle tone needs to change with position it is easy to see the necessity of these projections. Additionally, the autonomic effect that the reticular formation has are not restricted to blood pressure changes. The reticulospinal pathways drive the intermediolateral cell column and subsequently the autonomic system. The reticular formation involvement alone can account for visceral as well as somatic changes.

There are abundant vestibular projections to the cerebellum. The cerebellum has projections to the reticular formation, and directly and indirectly to the thalamus. These projections can account for autonomic changes via the thalamohypothalamo pathways, and cortical changes from projections from the thalamus to the cortex. Also, the cerebellum modulates movement via cerebellobasalganglionic and cerebellothalamocortical projections. And finally, the reticulospinal and vestibulospinal pathways modulate trunk flexion and extension.

Additionally, the vestibular mechanism projects directly to the thalamus and hypothalamus. The thalamic projections are thought to account for cortical appreciation of position changes. And the hypothalamic projections are thought to be necessary for autonomic response to movement.

After examining the three possible mechanisms for the effect of cranial manipulation it is easy to see that the vestibular apparatus has the largest potential for affecting change on the central neuraxis and consequently the overall physiology. However I also find it difficult to completely ignore the possibilities of dural feedback from the mechanoreceptors located there. So the conclusion that I would draw, with the available information, is that the vestibular mechanism is the primary mechanism with the dural mechanoreceptor mechanism secondary.

If one takes into account the vast neuronal network affected by the vestibular mechanism it is easy to account for the far reaching effects that cranial manipulation can have on the health of the patient. If the practitioner has these pathways to memory and available for explanation it will be effortless for him to explain to other practitioners why he is getting such fabulous results from his treating techniques. This should be another example as to why we need to have a greater understanding of what we are accomplishing when we are using manipulative therapies.