Part 1 of 3
Carl DeStefano DC CAC DACNB FACFN
Dena Jersild CAC DVM
Veterinarians and Chiropractors studied neurology in school and should have a basic understanding of how to perform a neurological exam. For those of us engaged in animal chiropractic, performing a good neurological exam is critical. A well-trained animal chiropractor is a functional neurologist who understands the pertinent neuroanatomy and neurophysiology needed to interpret patient history and objective findings. Where we differ from our traditionally trained brethren is in our ability to appreciate the subtleties of a multi-modal integrated nervous system. Where a traditional approach to the neurological exam is to a simple yes or no answer evaluating for disease,
the chiropractic neurologist is sensitive to degrees of function. We understand that the nervous system can work less than optimal without being diseased. With this distinction in mind we can utilize different windows into the nervous system that evaluate for frequencies of firing of pools of neurons. Our goal would be to return the nervous system to the highest degree of function allowed by the animal’s genetic potential.
Certainly the diagnosis of neurological pathology is an important goal of any neuro exam yet the presence of functional neurological deficiencies is much more common and thus much more likely to be of benefit to the majority of our patients. Our presentation is designed to teach the animal chiropractor those aspects of the neurological exam that can be used to evaluate the functional integrity of neuronal pools. Treatment can then be aimed specifically at those areas of the neuro-axis compromised from pathology or from a decreased frequency of firing of a pre-synaptic pool. Since animal chiropractors use receptor based therapies as their therapeutic tool we are unique in our abilities to specifically reach pools of neurons by modulating receptor potentials.
Before we begin the neurological exam an understanding of certain neurophysiological concepts is necessary.
Central Integrative State and Animal Health
There is probably very little argument that the central nervous system (brain and spinal cord) runs things; at least in the physical body. The nervous system directs healing and maintains health. There is nothing beyond the awareness of the nervous system. Information is received and transmitted throughout the neuro-axis by chemical and
electrical means. Synaptic transmission of information is well understood and the sensitivity of neurons can be modulated by chemical and electrical factors. A total of all excitatory and inhibitory influences from temporal and spatial pre-synaptic influences define the central integrative state of a neuron or pools of neurons. A good chiropractic neurological exam seeks to define the central integrative state at the differing longitudinal levels of the neuro-axis.
Animals Don’t Come With Batteries
If the central nervous system drives all aspects of biology, what drives the central nervous system (CNS)? The answer is critical because it explains why our therapies are so effective. The central nervous system is driven by the environment! The greatest and only constant environmental stressor is gravity. The forces of gravity are transduced into electrical signals by mechanoreceptors. These include muscle spindle cells, golgi tendon organs and other proprioceptors. Gravity’s influence on the CNS via mechanoreceptors is responsible for approximately 80{eb61268fbf49bcfdcf52579ac5fca6511a192c673ba6f2ea599fadfe3e39119a} of the baseline activity of the neurons of the CNS. In other words, in the absence of normal gravitational forces, all neuronal function would be severely hindered making neuronal death, over time, highly probable.
A very high percentage of the mechanoreceptor population lies in close proximity to the spine in the form of joint mechanoreceptors in the ligaments and joint capsules of the spinal segments. In addition, the muscle spindle cells (MSC) and golgi tendon organs (GTO) of the intrinsic muscles of the spine have great influence on central nervous system integration. This is due to their sheer numbers as well as the fact that as midline structures they were phylogenetically responsible for the evolution of the structures that developed more laterally. Loss of intersegmental motion (fixation), or aberrant motion (subluxation), reduces the frequency of firing (temporal summation), and numbers of mechanoreceptors firing (spatial summation) into the central nervous system. Since incoming sensory information is divergent in nature, loss of firing of only a few receptors can have tremendous impact on CNS health and integration.
Receptors
Receptors are neural structures that transduce an environmental stimulus to an electrical message. There are differing receptors to transduce different types of environmental stimuli. The retinal receptors transduce light and the auditory receptors transduce sound etc. These are examples of receptors that perceive the external environment. There are receptors that perceive the internal environment of the animal such as temperature, pH, hormone levels etc.
As sensory information enters the spinal cord and brainstem via a sensory neuron it diverges via collateralization. In other words one sensory neuron will synapse with many post-synaptic neurons that will in turn synapse with many other post-synaptic neurons which will modulate the central integrated state of each neuron in its path.
The central integrated state of a neuron can be defined as the sum total of all the excitatory and inhibitory influences on the neuron. The central integrated state of a neuron will determine the probability of that neuron firing.
If there is a decreased frequency of firing of any sensory receptor the post-synaptic pool of neurons will at some point begin to undergo trans-neural degeneration.
Trans-neural Degeneration
All neurons need oxygen, glucose and active electrical stimulation to remain healthy. When a neuron is fired, second messengers activate genetic material in the mitochondria and nucleus. These immediate early gene responses direct the production of more mitochondria and new protein within the cytoplasm. This protein is used for structural purposes as in the production of organelles and microfilaments. Protein as enzymes direct metabolic processes. The mitochondria are the site of oxidative phosphorylation where glucose is metabolized to produce ATP. This ATP is used in part to run ion pumps that maintain the electrical and chemical gradients of the cell. Protein is also greatly responsible for the negative charge within the cell.
With decreased frequencies of firing, secondary to loss of receptor stimulation, protein production is slowed or stopped and the numbers of mitochondria within the cell become less. Energy for cellular function is then more likely derived from the anaerobic pathway of glycolysis. Lactic acid levels rise creating ferrous iron free radicals, poisons to the neuron. With less mitochondria there is less ATP produced to power the ion pumps. Hydrated Na+ ions now accumulate within the cell. Less protein means less structural integrity and less negativity within the neuron. As the equilibrium potential of the cell is slowly lost the neuron begins to swell. This process of degeneration is known as trans-neural degeneration. The next step is cell death.
The mechanism described above occurs to some degree in all neurons in a particular neuronal system. The probability that a particular neuron will be affected by a pre-synaptic decreased frequency of firing from a receptor field is dependent on the pre-existing health of the neuron (i.e. central integrated state), and other collateral influences on that neuron from homologous pathways. In other words, maintaining adequate frequencies of firing to neuronal pools via prophylactic receptor stimulation can protect these cells in times of injury or disease when receptor stimulation is less. Driving frequencies of firing via exercise and the specific treatment modalities taught in our program lead to long-term potentiation, a phenomenon where increased frequencies of firing are maintained in a cell long after the original stimulus has ceased. This increased drive to the genetic machinery of the cell causes positive growth of the cell. More mitochondria and other organelles increase the stability of the neuron. Budding or dendritic spur formation occurs increasing the surface area for synaptic communication with other neurons allowing for more efficient exchange of information. This explains the clinical observation that in general animals that are regularly exercised and /or are receiving prophylactic chiropractic care have an easier time recovering from injury and illness.
The Brain has Two Output Systems
Sensory information diverges all the way to the brain. It is at the brain that a response to the incoming sensory information is initiated. As incoming sensory data from receptors is integrated, an appropriate response is directed down through motor pathways converging on two motor output systems. There are only two output systems from the central nervous system. One motor output system is to somatic muscle via the ventral horn and the other is to the autonomics via the intermedial lateral cell column. This makes great sense. As the animal moves in response to environmental stimuli there is concurrent activation of the autonomic system to support that movement by shunting blood to the appropriate muscles, releasing glucose stores, increasing cardiac output, etc.
In a perfect world sensory information from the environment is transduced to an electrical message that diverges to many post-synaptic neurons. This allows integration of information arriving from different anatomical sources as well maintaining the health of those cells via optimal gene expression. At the brain, motor responses are sent through a converging system to effect somatic muscle and the autonomics.
In a not so perfect world (the world in which our animal patients live), there are many environmental stressors that aberrantly affect receptors activation directly or the central nervous system indirectly. Early chiropractic educators expressed this idea philosophically. Structural, chemical and mental stressors were described as the cause of dis-ease. We now know, scientifically, that they were absolutely correct. Dysafferentation as a result of segmental dysfunction sends faulty information to the central nervous system. Like a smudge on a camera lens, subluxations, fixations and old injuries can send an unclear and inaccurate picture of the world to the central nervous system. Poor nutrition, environmental pollution, inappropriate use of pharmacology and vaccines, lack of exercise and psychological stressors add to failure of normal, healthy central nervous system integration. Inappropriate muscle and autonomic responses are the natural consequence. Unstable joints increase the probability of injury, gait abnormality and performance deficits.