CN III. Oculomotor Nerve
“The oculomotor nerve originates from motor neurons in the oculomotor (somatomotor) and Edinger-Westphal (visceral motor) nuclei in the brainstem. Nerve cell bodies in this region give rise to axons that exit the ventral surface of the brainstem as the oculomotor nerve. The nerve passes through the two layers of the dura mater including the lateral wall of the cavernous sinus and then enters the superior orbital fissure to access the orbit. The somatomotor component of the nerve divides into a superior and inferior division. The superior division supplies the levator palpebrae superioris and superior rectus muscles. The inferior division supplies the medial rectus, inferior rectus and inferior oblique muscles. The visceromotor or parasympathetic component of the oculomotor nerve travels with inferior division. In the orbit the inferior division sends branches that enter the ciliary ganglion where they form functional contacts (synapses) with the ganglion cells. The ganglion cells send nerve fibers into the back of the eye where they travel to ultimately innervate the ciliary muscle and the constrictor pupillae muscle.”
Guillaume Latendresse from the Minnesota Wild got strapped into Dr Ted Carricks GyroStim chair invented by Kevin Maher, who spent seven years perfecting the chair to help his little daughter overcome her cerebral palsy deficits, essentially unable to right herself. At first he and his wife were rolling or turning their little girl to stimulate her vestibular/balance system hundreds of times a day which was suggested to them by one of the many neurologists they had consulted, concerning their little girls affliction. Being a mechanical engineer, Maher came up with a better idea to rotate/stimulate his daughter’s brain which became the first GyroStim chair. His little girl went much much farther in her development then expected. Now she walks with the aid of crutches and has a A+ average in high school. So what does the GyroStim chair have do to these two brains, Maher’s daughter and Guillaume Latendresse? Lets look at the descriptions of the language from Latendresse about his post traumatic brain injury or other people, like Sidney Crosby who also went through GyroStim stimulation with Dr Ted Carrick probably because Pat Brisson is the hockey agent for both players. Concussed people talk about ‘foggy eyes’ in which they have a hard time tracking things with their eyes, they complain about not being able to watch television, they can’t read and bright lights bother them a lot. Lets stop right there and do some eye movement 101, let’s go!
The oculomotor nerve runs from the mid brain stem with two groupings straddling the mid-line, the closest is the Edinger-Westphal, the next, just adjacent is oculomotor nucleus grouping then these axons join running along underneath the brain to innervate the eye muscles for each side.
Opposite pairs of eye muscles contract to control eye position as you change gaze, horizontally side to side, the inner Left with the outer Right and the outer Left with the inner Right. Each outer/cheek side eye muscle is called an inferior rectus muscle (L + R), each inner -close-to-the-nose muscle is the medial rectus (L + R). If you use both L + R medial rectus you are tracking an object getting closer until your eyes completely cross. Lifting your gaze up requires the contraction of the muscle on top of the eye nearest your forehead which is the superior rectus muscle. The nerve cell origins in the brain stem the oculomotor nucleus control the rectus muscles, superior, inferior and medial, the inferior oblique, rotating the eye to the periphery and the eyelid muscle, the levetator palpitator superioris which coordinates raising or lowering the eyelid as the eye moves up or down. The Edinger-Westphal nucleus controls the iris ciliary muscle, changing the shape of the eye lens and the pupillary sphincter muscle , controlling the diameter of the pupil, depending on brightness/darkness intensity of light conditions. So what did the hockey concussed players complain about again ? They complained about the ‘fogginess’ of using their eyes the brightness, the visual motion. They talked about their oculomotor system being out of whack. But there’s more physiology to the fogginess of their eyes, there is also their balance system, because the eyes orient to a gravity field, to our standard vertical orientation. Now both Latendresse and Crosby and Maher’s little girl were rotated in the GyroStim chair, what happened to the coordination of the eye orientation, what happened to their neck muscles as their bodies were temporarily upside down? How does the brain function in the reverse situation of firing muscle contraction when the orientation is now opposite to what gravity usually is? As usual things now get interesting. I had to search the PubMed literature to try to get a handle on this kind of situation of muscle firing upside down. Here’s a start: Electromyographic Activity of Dorsal Neck Muscles in Squirrel Monkeys during Rotations in an Upright or Upside Down Posture by J. Eric Killian and James Baker J Neurophysiol 93:2587-2599, 2005
In the authors introduction they describe, ” Both the vestibulocervical (VCR) and vestibulocular (VOR) reflexes compensate for head movement. In the case of the VOR, head movement produces opposing eye movement that keeps images still on the retina. In the case of the VCR, however, head movement produces opposing neck muscle activity that minimizes the head movement itself. Thus the VCR differs from the VOR in being a closed loop negative feedback system: its output directly affects its input and it does not rely on another system( the visual system in the case of the VOR) for calibration.”
“While the VCR (this pathway mediates head position by reflex activity of the neck muscles in response to rotational; acceleration of the head) whatever the position of the head in space, righting reflexes work to return the head to the upright position with respect to gravity. Righting reflexes are an elaborate sequence of behaviors drawing on visual and vestibular inputs and operating over the neck, shoulders, torso, an limbs. Head and shoulder-righting reflexes are dependent on an intact labyrinth. The overall conclusion from neck muscle electromyogram (EMG) studies is that semicircular canals provide the predominant neural signals for the VCR and head stability and otoliths that signals for righting and upright posture. (The vestibular labyrinh is continuous with the cochlea (the middle ear), and consists of two otolith organs, the utricle and saccule including the three right angled with each other semicircular canals). Compensatory and righting reflexes are synergistic when an animal is upright but antagonistic when the animal is upside down.”
“Rotation of the head about an earth-horizontal axis produces vestibulocervical reflexes that may be driven by several different central signals of vestibular origin, including signals derived from the semicircular canals related to head rotational head velocity or related to static head tilt with respect to gravity. That central control signals are shared by the VOR and the VCR is supported by the projection of many vestibular neurons to both oculomotor nuclei and the spinal cord.”
The authors conclude with the comment that righting reflexes will be a challenge for future experiments to be characterized in relationship to overall control of the head are better understood. “…..neck muscle EMG in response to head rotation is a combination of stabilizing and righting reflexes, with stabilization mediated by semicircular canal signals that are most clearly evident in the upright head posture and with the righting mediated by the utricular signals that are most clearly evident with the head down. Neck muscle reflex activity appears to reflect varying degrees to which an animal relies on stabilizing versus orienting reflex systems.”
Sherrington remarked in 1898, that, “reflexes are distinguished by rapid, autonomous, and predictable action, all presumed to originate in simple, fixed circuitry.” Sherington could not imagine the actual plastic nature of the brain back in the end of the 19th century. “However, even the simplest of neural pathways are subject to control by other neural systems, to adaptation or habituation, and to alteration of action in response to stimulus context.” So as you can see even the researchers skilled in the domain of inverted gravity have a difficult time deciphering the exact mechanisms on the normal head orientation, let alone what happens in a concussed brain. But the GyroStim appears to use the plastic nature of the brain to rewire itself to accommodate the new gravity vector stimulus in essence, rebuilding the brain. Maher’s daughter, Sidney Crosby and Guillaume Latendresse are all active people with balance posture brain changes following their vestibular recalibration.
I am honored that this blog essay when it was first published May 3, 2012 is being used currently as of May 5, 2012, by http://www.GyroStim.com on their web site to promote discussion as to how the vestibular stimulation may be functioning to resolve some of the serious symptoms and complications following traumatic brain injury. I would also like to mention that FDA approval has not yet been achieved so treatment options can be fully documented. But there is little doubt in my mind that the GyroStim stimulation is a huge jump toward changing aspects of the plastic nature of the brain to achieve changes.
Science can be very nasty at times with the publish or perish attitude that sits at the foundation of grant funding. Now let me remind the reader that during previous attempts toward grant funding to approach the source of funding some of our return comments are such like, “..it’s not neurological enough.” Or perhaps we were in the wrong selection group I don’t know. But there is a tendancy to promote topics in a framework of what is acceptable given the current understanding. If you wander outside that you are in for serious challenges. But that is not how Nature works, which is what we are always trying to accomplish at least in our own little group. It’s not what the reviewers want or expect it’s about the seriousness of,’ How does Nature really do this?’ That is our guiding mantra that is what makes us vibrate. Scientists are possessed to be the first to get the first explanation. Here’s my answer to that. We don’t own Nature- never have- never will. We are on the side looking in at the wonder of how it all works in such intimate harmony plus how easily it looses this harmony in damage or disease states. To puff out your chest and strut around displaying “I got there first” is such a cartoon. Nature has been around for billions of years the fact that anyone got 0.000000000000001 percent of how something works and says “I got there first” is sheer simplicity and puffery, the tragedy of the human condition.
So what does this essay really mean about trying to better understand concussions? I think that two things are happening here. The first is this whole eye/balance neck muscle response where your head and eyes are positioned within a gravity field is, ‘going off’ following a concussion, let’s call it an oculomotor concussion within a brain concussion. I suspect these are two major events within a global concussion plus probably more as we tease out the details. Then there is the second aspect that concussions when viewed over a few decades appear to accelerate aging which has been recently just reported, by a group from the University of Montreal. Recalling an earlier blog essay from cerebrovortex on the tensegrity zone behaviour happening within the vulnerable medulla mid brain that is the second aspect of the concussion problem, that affects a whole bunch of autonomic systems. That’s how I understand it as of now. Hopefully in a bunch of time we achieve more detail as we patiently teach ourselves as the observers of what is changing during a concussion, how can we accurately measure it? Can we shift brain deficits by some means of a specific treatment, like brain cooling? Here’s a final thought: But even as individuals when we engage to make a difference: to bring light to darkness is to bring joy to the toil of challenging the understanding, despite how small we really are.