In April 1999, Dr. Sherry (Dickholtz) Gaber published an article in the Upper Cervical Monograph, reprinted here.
I was chatting with a horse owner about the majesty of her horse. While admiring him I said, "Did you know your horse has a head tilt?" She replied, "No, but now that you mention it I can see one eye is lower than the other and it is even small in size." Objectively, the right eye was lower than the left by 1/4-1/2 inch. "Is that a significant symptom?" The owner questioned as she untied him from the crossties. Then she said, "Watch how he moves, he's been doing this for quite awhile." The horse looked beautiful as he moved out, and then I saw it, his right rear leg exhibited characteristic stringhalt type gait (an involuntary flexion of the hock during forward motion) along with a delayed motion while the leg was coming down. The owner then asked "Can you do anything for this chiropractically?"
These are the questions I asked myself:
There's a difficulty in walking, there's head tilt, and the cerebellum is not level, so could there be an occipital, atlas or combination of the two that could lead to this neurological deficit and abnormal muscle control to the rear limb area?
Could the uneven eye level be communicating to the cerebellum that the horizon is not horizontal, therefore, the paraspinal muscles are adapting to that incoming optic information?
Could a long-standing condition of inappropriate adaptation be too stressful thus leading to symptoms?
Could there be a brain stem (medulla) are misalignment blocking or affecting the proprioception tracts?
So the question is: How and why can head tilt effect proprioception tracts, gait, optic and postural muscle control and coordination activity of an animal? It is through the brain stem neurology and associated tracts that allow the head and upper cervical area to control spinal and limb musculature. To understand these mechanisms let us review some basic neurology and anatomy.
Postural muscle control and balance comes from a few control centers. One of the major players is from the 8th cranial nerve, the vestibulocochlear nerve. This nerve gets initiated through the inner ear, which contains semicircular canals, which picks up information by means of flowing endolymph which bend small hair cells whenever the head tilts. The hair cells communicate with nerve fibers that lead to the vestibular nuclei (the spinal, the superior, the medial and the lateral nuclei) or to the cerebellum.
The 4 vestibular nuclei send their axons either to the cerebellum or to one of two tracts: the medial longitudinal tract or the lateral vestibulospinal tract. The medial longitudinal tract receives input from the superior, medial and the spinal nuclei. The lateral vestibulospinal tract receives information from the lateral nucleus. Let's review how these two significant tracts communicate to the limbs and spinal muscles with the information they are receiving from the inner ear and cerebellum:
The medial longitudinal tract: conveys messages to the nuclei of the eye muscles, to the cells innervating the muscles moving the head, the neck, the spinal accessory nuclei (cranial nerve XI), and the muscles of the trunk.
The lateral vestibulospinal tract: enters the cord in the anterior fasciculus and ends on the motor neurons of the muscles of the limbs. It is through the vestibule reflexes that act on the neck and on the limbs (vestibulospinal reflex) that are evoked principally by sensory input from the otolith organs.
Let's dissect these nerve tracts and muscle innervations a bit more and see how the tracts affect muscle function directly.
The medial longitudinal track sends fibers to:
The nuclei of the eye muscles -- Cranial nerves III (oculomotor), IV (trochlear), and VI (abducens)
Muscles that move the trunk
Muscles that move the head and neck -- i.e. through the spinal accessory nuclei (cranial nerve XI)
The spinal accessory nuclei function: controls the trapezius,
sternomastoideus and cleidomastoideus muscles
Trapezius -- insertions; spine of the scapula
Origin: ligamentum nuchae
Action: elevates the front legs, moves the
shoulder cranially and caudally
Problem: neck inflexibility, extension problem,
shoulder spasms, scapula malposition
s.m. - Could a chronic misalignment, effecting the
spinal accessory nuclei, effecting the trapezius
function, finally lead to a wobbler type syndrome?
2. The lateral vestibulospinal tract sends fibers to muscles of the
The proprioception and touch travel needed for foot placement comes from the dorsal spinocerebellar tract. At the upper spinal levels the dorsal columns can be divided into two bundles (fascicles) of axons: the gracile and the cuneate fascicle. The gracile fascicle ascends medially and contains fibers from the ipsilateral sacral, lumbar and lower thoracic segments. The cuneate fascicle ascends laterally and includes fibers from the upper thoracic and cervical segments. The two bundles terminate in the lower medulla in the nucleus gracile and cuneatus. Together they are called the dorsal column nuclei.
The pathways used to carry information from the upper limbs are from axons in the cuneate fascicle, which then synapse in the cuneate nuclei. The pathways for proprioception of the lower limbs use the gracile fascicle and synapse in the gracile nuclei. Various sources report that the medulla is about 1 inch in length and is located from the border of the foramen magnum to the inferior border of the first cervical vertebrae (the atlas). These tracts communicate to the cerebellum and to the medulla at a rate of 150 meters per second (1-1/2 football fields per second!). If these tracts have interference, then by doing the righting reflex, by turning over the paw, the result will be a delayed righting reflex. One can see an incredible change with this reflex after the medulla has been cleared from any misalignment.
Reticular Formation Control Mechanism
In the reticular formation of the pons and the medulla there were two groups of nuclei identified that were involved in the control of posture. The nuclei in the pons facilitated spinal reflexes. The nuclei in the medulla inhibited spinal reflexes. These nuclei project through the medial and lateral reticulospinal tracts to ALL levels of the spinal cord. These are the tracks that are utilized when delivering an upper cervical adjustment; muscular reflex changes throughout the body can be seen. The pontine reticular formation projects down the cord through the reticulospinal tract and terminate on and facilitate motor neurons that innervate axial muscles and extensors of the limbs. The medullary reticular formation gives rise to the lateral reticulspinal tract that projects bilaterally down the front of the lateral columns. This tract produces inhibition of neck and back motor neurons, similar to the medial vestibulospinal tract. This tract, importantly, makes polysynaptic inhibitory connections with extensor motor neurons and excitatory connections with flexor motor neurons. This tract can also excite motor neuron innervating extensor muscles and inhibit flexors! Obviously a tract to absolutely make sure is clear from a misalignment, otherwise any gait movement can be compromised.
Both medial and lateral reticulospinal fibers also modulate reflex action during ongoing movements and produce different effects, depending on the movement in progress at the time...These fibers coordinate posture and movement by integrating vestibular and other sensory inputs from the cerebral cortex. These centers and tracts are ultimately important to understand because postural adjustments are governed through the corticoreticulospinal system that was explained above.
Parasympathetic Blood Supply
The parasympathetic control on the arterial system allows for proper dilation while the body is at rest. Arteries abnormally contract resulting in abnormal blood pressure and slowed healing properties. Recall the pathway for the vertebral artery, ascending through the cervical transverse foramina through the atlas transverse foramina, then through the foramen magnum to the cerebellum and the Circle of Willis, which then supplies oxygenated blood to the rest of the brain. Keep in mind the possible effects the cerebellum and brain might be receiving from a misalignment resulting in tractionizing the vertebral artery!
So, did I answer the owner's second question: Can I change the stringhalt gait? At that moment I saw a typical pattern of both atlas and occiput misalignment causing the medulla to be compromised. In this case the atlas was misaligned superiorly (high) on the condyles on the right and the occiput was tilted inferiorly on the right (AVCA listing: ARS and OLS). I believe it was the right side of the occiput leaning into the medulla, effecting the lateral reticulospinal tract that was causing more of the neurologic deficit. The result was abnormally contracted muscles down the right side of the spine to the rear limb and proprioception tract interference at the medulla. I adjusted the occiput as OLS, while the owner braced the atlas on the right side. Then adjusted the atlas as ARS. The eyes leveled and opened with an equal opened appearance. Assessing the eyes can clue you in on this whole neurological circuit. I asked the owner to walk the horse. He automatically walked off about 70% improved! This neurology works when cleared from the boney misalignments. Some time has elapsed and the horse has stayed under chiropractic care. To date there have been no other characteristic signs of stringhalt or a delay in gait.
Conclusion: The body has many reflexes and compensation mechanisms to maintain balance. It is fruitful to think of the cerebellum as a center, which received enough information, both from the periphery and from the cerebral cortex, to set the mechanisms for appropriate postural and dynamic control. Allowing the cerebellum's structure to be level, a proper balance of posturing muscles and alignment with the skeletal structure can be attained. Ultimately -- it is good to ask the question: Do You See Head Tilt?
The Ciba Collection. Frank Netter, M.D.
Principles of Neural Science: Kandall, Schwartz, Jessell
Textbook of Medical Physiology: Guyton
Ceronal Module: Dr. Sharon Willoughby