This is by far the most technical installment of the article series, which is why we broke Part 4 down into two subsections. I encourage you to read through it a couple times. Depending on your current level of knowledge and experience, there may be parts that are difficult to understand given, but coming back to this piece a few times will enable you to comprehend a little more each time.
UPPER CERVICAL FUNCTION AND BALANCE
The upper cervical spine maintains an intimate relationship with the cranium, the masticatory apparatus, the eyes, the vestibular system and the CNS. This is because every nerve that leaves the foramen magnum passes through the atlas. The upper cervical spine is also intimate with the vestibular system and visual system in producing the majority of the body’s righting, equilibrium and tonic neck reflexes.
|Properties of Tonic and Phasic Musculature
|Predominantly Tonic Muscles
||Predominantly Phasic Muscles
|Prone to Hyperactivity
||Prone to Inhibition
|Susceptibility to Fatigue
|Reaction to Faulty Loading
|Shoulder Girdle - Arm
|Pectoralis Major & Minor
||Deep Neck Flexors
|Lumbar and Cervical Erectors
|Pelvis - Thigh
|Tensor Fasciae Latae
|Lower Leg - Foot
||Extensors of the Toes
Because of environmental challenges that we faced during our developmental years it was, and still is, critical that our optic (eyes), otic (ears) and occlusal planes maintain horizontal relationship relative to the long axis of our bodies or what is known as horizontal gaze.
The position of horizontal gaze can also be referred to as a "zero" point, or point of reference for the eyes, vestibular system and masticatory system (above, A). Because the eye musculature is made up of striated skeletal muscle tissue, if a horizontal gaze is not maintained as the physiological rest position, or "zero" point, there will be chronic loading of specific eye musculature that can lead to trigger point development and length/tension changes in the eye muscles. Any deviation from the "zero" point will result in a discharge of motion and position sensitive receptors and nerve endings in the vestibular system and reflexive changes in muscle tone. Because the mandible is a floating bone, any alteration of the position of the cranium from the "zero" point will change occlusal relationships, resulting in a hit-and-slide occlusal compensation. As I stated in Part 3, a hit-and-slide compensation is perceived as a stressor to the body, from our nervous system’s perspective, we won’t live very long without teeth.
Due to the absolute necessity of maintaining optic, otic and occlusal relationships in the plane of a horizontal gaze, maintaining the "zero" point as the point of reference from which ocular, cranial, masticatory and cervical motion is initiated from, any structure below the craniocervical junction becomes sacrificed to these survival objectives. When the upper cervical spine is subluxed, the whole body below it will adjust, and should anything alter orthopedic relationships below the craniocervical junction (such as a shortened leg secondary to a fracture), all structures below the head will be sacrificed to regain horizontal gaze. In other words, the head always wins – if the head is out of alignment and "zero" point is compromised, everything else below will compensate to ensure the head regains its horizontal gaze! For example, should the naso-respiratory system be threatened for any reason, be it allergy, faulty breathing habits, craniofacial growth and development disorder, or an underdeveloped oral airway, the head will migrate forward in attempt to restore ventilation, using the upper cervical spine and entire body below as a buffer system to accommodate this adaptation (above, B).
Aside from the vital task of maintaining optic, otic and occlusal relationships and being intimately involved in equilibrium and righting responses, the upper cervical spine is highly vulnerable to subluxation, or what is technically referred to as the atlas subluxation complex (ASC). This is because of the unique architecture of the atlas-axis system. The atlas and axis are most vulnerable to the possibility of true subluxation because they are the only two vertebrae in the entire spine that do not have interlocking bony facets and they have fewer muscular and ligamentous attachments. The ASC causes more widespread effects throughout the human organism than those of subadjacent areas and has been shown to subluxate in commonly recognized patterns (above).
Clinically, the ASC may be related to many aspects of craniofacial pain, postural and balance dysfunctions and can be the driving force behind any number of conceivable musculoskeletal disorders. This is because, as demonstrated by the Survival Totem Pole, the upper cervical spine reigns superior to the viscera, emotions, sacrum/coccyx system, pelvic girdle and all remaining joints, which I call slave joints. (It is important to note that the emotion symbol of the Survival Totem Pole - seventh from the top - is what I call a floating symbol because the emotions of the body are powerful enough to alter any physiological system, including respiration.)
How does this relate to you as a trainer?
It is important to be aware of the profound influence the upper cervical spine has over the rest of the body and that, unbeknownst to you, you may have clients with an upper cervical subluxation, which is causing a myriad of problems in them. Having a subluxation of the upper cervical spine is generally not as obvious as having a bloody nose and chances are your client is not even aware they have an ASC.
The influence of an ASC is believed to come primarily from:
- Influence of mechanoreceptors and nociceptors (pain fibers) of the upper cervical spine
- Traction of the cord by the dentate ligaments
- Shifts in the center of gravity (CG) of the head and pelvis to maintain stability
Each of these influences will be examined individually and will have a brief summary covering what was discussed, the first point here and the second two in Part 4B of this article series.
Upper Cervical Influence of Mechanoreceptors and Nociceptors
Factual evidence strongly suggests that an atlas adjustment (from a properly trained NUCCA chiropractor) has an effect on the entire nervous system, primarily through its effect on joint mechanoreceptors. Subluxation on the other hand, may similarly produce opposite results through the same mechanisms. Type I, II and IV joint capsule receptors are well recognized for their tonic, phasic and nociceptive influences respectively, with type I and II making a major contribution to postural sensation.
The type I tonic mechanoreceptors maintain a resting discharge frequency of 10 to 20 impulses/sec as a result of intracapsular pressure and tone of muscles attaching to the capsule. They are located mainly in the superficial layers of the fibrous capsule and are more numerous on those aspects of the joint capsule that undergo the greater changes in stress during natural joint movement.
Because of the complex mechanics of the C0-C1 and C1-C2 joints, any subluxation of the atlas or axis will likely disturb head posture through coupled movements (above, A-D). Grice references Dankemeyer and Rothmeier for their early observation of asymmetrical atlas-axis interodontoid space being associated with abnormal lateral tipping of the head. Dvorak and Dvorak demonstrate that with cranial side bending, there is coupled ipsilateral rotation (to the same side) of the axis followed by lateral translation of the atlas to the same side.
D. Seemann of the National Upper Cervical Chiropractic Association research advisory board, states that the lateral movement of C1 on the condyles of the occiput is responsible for the detriment to the central nervous system. Displaced laterally, C1 is positioned to be the interference that causes a loss of the inhibitory influences of the reticular formation in the brainstem at its caudal end on the extensor muscles. Although this is only one example of a potential subluxation pattern, the association has identified four basic subluxation types (above, A-D) and approximately 10,000 variations through long-term X-ray studies.
The altered joint positions of subluxation are deviations from anatomical neutral and thus will likely stimulate the type I and II joint receptors accordingly. In fact, any stimulation of the proprioceptive apparatus, by virtue of its reflex connections, will modify the firing rate and the recruitment of alpha motor neurons and will therefore force the selection of a new length-tension curve. Alteration of muscle tone is the earliest cause of aberrant biomechanics, or pathomechanics. Muscle tension will also affect the subluxation and the degree of subluxation of the facets. Clinically, alterations of muscle tone, most often hypertonicity, are palpable in association with both the ASC and FHP, and active trigger points can be expected. This again leads to several mechanisms for developing a pain spasm cycle with relative ischemia and high potential for pain referral into the craniofacial region, including nociceptive stimuli (pain stimuli) bombarding the sensory system at the upper cervical levels of the cord, which has been demonstrated clinically to cause the balance apparatus may behave abnormally.
The type IV (nociceptive) receptor system is activated when its constituent nerve fibers are depolarized by the generation of high mechanical stresses in the joint capsule containing it, as occurs with abnormal neck postures. The afferents from the type IV receptor system of the cervical spinal joints exert powerful reflexogenic effects on motor unit activity in neck and limb musculature. This causes the clinically familiar distortions of head and neck posture and gait that are associated with pain of cervical articular origin.
In 1940, Bertrand De Jarnette referred to the occipital atlas condyles and reported that any irritating factor of the spinal muscles attacks the last articulating portion of the spine with greater force than any other area. He theorized that when this occurs, the condyles close with a slip lesion and compress arteries that make up the circle of Willis in the brain. The medulla spinalis is engorged, swelling the membranes of the cord and producing spinal cord pressure on the rim of the atlas. When this occurs, cord circulation is impeded, and normal spinal cord physiology becomes pathology; all tissues inferior suffer, the weakest to the greatest degree.
The sympathetic ganglia of the cervical region are in close proximity to the vertebrae and anterior cervical musculature. The superior cervical ganglion is virtually sandwiched between the internal carotid artery and sheath, anteriorly, and the longus capitus muscle, posteriorly. Its position of being anterior to C1, 2&3 is such that fixation or mechanical derangement (torsional hypermobility) may cause reflex contracture of the muscles and put pressure on the ganglion. Atlas displacement can cause either bilateral or unilateral swelling and thickening of the muscles, exerting pressure on one or both superior cervical ganglion.
The superior cervical sympathetic ganglion receives preganglionic fibers through the sympathetic chain from the T1-T4 nerve roots. Sympathetic fibers also arise from the body of the ganglion and supply the C1-C4 nerve roots. It receives or supplies communicating, visceral, vascular, muscular, osseous and articular rami. It communicates with at least four cranial nerves or their branches, with the vertebral arterial plexus and occasionally with the phrenic nerve. This ganglion forms the carotid plexus, through which it reaches the eye and provides sympathetic fibers to the radial fibers of the iris, the ciliary muscles, as well as several extraocular structures. Among the other structures it reaches are the sphenopalatine ganglion and the mucous membranes of the nose and pharynx. It further reaches the vestibular and cochlear portions of the ear via the labyrinthine artery and the stylomastoid branch of the posterior auricular artery. Therefore, you can see that the ASC can easily alter balance indirectly by altering the function of the eye and naso-respiratory system and directly via influence on the vestibular system.
It has been known for over 25 years, that the arterial vessels on the surface and inside the brain are innervated by sympathetic nerve fibers that arise from the superior cervical ganglion. Vernon refers to Kobayashi et al., who found by stimulating the cervical sympathetic trunk of cats, that vessels smaller than 50 microns in diameter are largely responsible for regulation of cortical blood flow. This study and many others quoted by Vernon support the theory that aggravation of the superior sympathetic ganglion via the ASC may contribute a vascular component to the cervicogenic headache. Additionally, cortical ischemia may result in diminished motor control and balance being that the sensorimotor cortex works in an integrated manner with many other regions of the brain. Not surprisingly, loss of balance is a fairly common complaint among headache sufferers, particularly those with migraine.
Now consider that today many people think a headache is an asprin deficiency and regularly show up to the gym on some type of medication. Although they may not feel the pain commonly associated with the vascular component of their headache, which in this case is driven by an ASC, they are likely be at greater risk of falling when exposed to balance challenges and, in my clinical experience with headache patients, they don’t learn new motor skills nearly as well as when headache free and unmedicated.
Because of the proximity of the axio-atlanto-occipital joint to the anatomical textbook description of the reticular formation, chiropractic upper cervical specialists have speculated on various means of mechanical deformation by the subluxation directly to this area of the brainstem. The normal excitatory nature of the upper reticular formation supplies much of the intrinsic excitation required to maintain muscle tone in the antigravity muscles, providing a basis for support of the body against gravity.
During our evolution from quadrupedal to erect posture, there has been a shift in the relative perceptual and reflexogenic significance of the mechanoreceptors in the labyrinth of the internal ear and those located in the cervical spinal joints in favor of the latter. Mechanoreceptive afferent input is conducted along the nerve fibers with the greatest velocity of transmission, providing primary sensory experience to the reticular formation for modulation of descending control. Descending control includes the direct regulation of posture by inhibition and facilitation of synergistic and antagonistic muscle groups, ipsilaterally and contralaterally.
There may be reason then, to speculate that subluxation of any member of the axial-atlanto-occipital complex, which produces aberrant head-neck postures, will require an appropriate response from the reticular activating system. Seemann suggests that lateral subluxation of C1 on the condyles of occiput causes a loss of the inhibitory influences of the reticular formation in the brain at its caudal end (distal end) on the extensor muscles. This subluxation could encourage hypertonicity of the illiocostalis and longisimus muscles, which have cervical and occipital insertion, respectively. This may disturb cervical (spinal) biomechanics, becoming a source of altered balance due to the intimate relationship between the cervical spine, eyes, vestibular system and even the lumbar spine and pelvic girdle, which are intimate with the lower extremities.
In fact, disruption of cervical mechanics does not come as an isolated entity. As early as 1906, Dr. Lovett demonstrated the kinematic intimacy of the craniosacral system and demonstrated a working relationship of all spinal segments between during gait (above). While balance training is now trendy, in the hands of an unskilled trainer the likelihood of injury escalates dramatically. For example, it is commonly known that about 85 percent of people today will present with low back pain (LBP) at some time in their lives, and that low back pain is the most common orthopedic insult likely to be encountered in the clinical or gym setting. In fact, the rate of LBP among among active populations, such as golfers, is very high with 53 percent of male golfers and 45 percent of female golfers presenting with LBP on any given day. This rate is thought to be even higher among novice golfers with 63 percent suffering LBP at any given time!
The reason I highlight this fact is that LBP is an extremely common byproduct of the ASC. While Dr. Lovett’s “Lovett Brother” system explains the mechanical relationships (neurological relationships will be explained below), it is important for any rehabilitation or exercise professional to appreciate that many LBP patients (particularly those with a locked facet joint or a deranged lumbar disc) present with structural malalignment (above, Antalgic Posture Common Among Low Back Pain Patients). As I have mentioned earlier, the head always wins, and the spine, pelvis and lower extremities become buffers, or sacrificial joints, for the maintenance of optic, otic and occlusal planes at the "zero" point or level with the horizon.
Due to the reactive nature of balance training exercises and the fact that most LBP and ASC patients present with multiple muscle imbalances, early exposure and/or exposure by under-skilled exercise professionals is likely to both exacerbate muscle imbalance syndromes and elevate the risk of further injury, while at the same time facilitating faulty motor pathways! For this reason, assistance from a skilled physical therapist or CHEK trained practitioner is recommended.
The aberrant joint relationships, biomechanics, circulatory, reflexive and compensatory muscle changes, associated with the ASC, contribute noxious input to the trigeminocervical afferent and cervical sympathetic systems. This, by the same mechanisms ascribed above to the FHP patient, could initiate or exacerbate craniofacial pain, vertigo and poor balance. Most often the alterations of head-neck posture will tip an alert clinician, encouraging a thorough upper cervical evaluation (see skeletal head "E" above and note the normal craniocervical relationships, which can serve as a model of normal when looking for a craniocervical postural benchmark to check your client/patient against). With the knowledge that the spine and extremities serve as a buffer system for structures and sensory systems of higherarchial control and that the upper cervical spine complex is both inherently unstable and highly proprioceptive, it becomes obvious that to truly develop balance skills without unnecessarily risking all structures inferior to given point on the survival totem pole, an integrated assessment approach is vital. Currently, there is a severe lack of training in the exercise community, especially with regard to how much can be applied to the sea of relatively unhealthy and orthopedically dysfunctional bodies! There is also a tremendous lack of communication, networking and participation with exercise professionals from the medical community. Hopefully someday soon we will bridge that gap.
Part 4B will cover traction of the spinal cord by the dentate ligaments and cpmpensatory shifts of the center of gravity of the head and pelvis to maintain stability.