This is a summary of Chapter V of “The Sensitive Nervous System” by David Butler.
Neurodynamics is the study and relationship of nervous system mechanics and physiology. The testing protocols for neurodynamics assess the nervous system’s ability to lengthen, glide, and change amongst interfacing structures.
When discussing neurodynamics, it is important to think of the nervous system as a continuum. Mechanical, electrical, and chemical changes in one part of the nervous system affect other related parts.
Gross Movements and Dynamics
When having a nervous system, the following qualities, movements, and buffering capabilities are necessary:
- Slide, glide, strain.
- Elongate (think gymnasts) and return from elongated position.
- Compress (ulnar nerve during elbow flexion).
- Stength (kicking a field goal).
- Jolting (whiplash).
- Repetitive forces
- Fluid/chemical selectivity.
Neural Connective Tissue
These include the meninges, nerve root complex, and peripheral nerve structures. Broken down as follows:
- Dura mater (outer, tougher)
- Arachnoid mater
- Pia mater (inner, thinner)
Nerve root complex
- Dorsal and ventral roots
- Spinal nerve.
- Mesoneurium – Sheath that surrounds a nerve. Contracts like an accordion to glide along adjacent tissues. Can become fibrotic with injury.
Meningovertebral ligaments – anchor down to spinal canal, which could become symptomatic.
Rectus capitus posterior is connected to the dura mater between the occiput and atlas; helping the dura fold. Makes you wonder what you are truly doing when you release this structure.
The sympathetic trunk’s proximity to the spinal column makes it susceptible to increased loads with upper cross syndrome.
Meninges are one of the components that may be represented by bilateral receptive fields (see chapter II). This could lead to dorsal irritation felt over a wide, bilateral, nondermatomal region. Dural pain is truly nociceptive, and may occur far from the irritated location. The leptomeninges (arachnoid and pia maters) also have mechanoreceptors, which make it responsive to movement.
The peripheral nerve’s connective tissue sheath is also very sensitive, as it is loaded with free nerve endings and pacinian corpuscles. There are also unmyelinated nerve fibers which contain pain neuropeptides. This component may demonstrate the sheath’s role in neurogenic inflammation.
Space and fluid
There really is no space in the nervous system, as everything is filled up with something.
Axoplasm is the nervous system’s juice, as it carries materials such as ion channels and neurotransmitters throughout. Axoplasm flows at 100-400mm per day, but during ischemia or physical constriction it may decrease or even stop. This substance is also thixotropic, meaning that flow is improved the more movement occurs. This is one reason why poor prolonged postures such as sitting for too long can become uncomfortable.
Blood Thirsty Neurons.
The brain and spinal cord make up 2% of body mass, yet consume 20% of available O2 in blood.
Brain and Spinomedullary Angle
The brainstem and cranial nerves move as the body nerves, and even a mild brain injury (think whiplash) can be associated with chronic pain.
The spinal cord is arranged in folds and spirals which straighten as the cord elongates, with most stretching occurring at the cervical spine. This attribute allows for increased cord protection.
Symptoms may arise from either the neural container/mechanical interface or the nerve itself, so both must be checked.
The sequencing of movements also affects the system’s response. This concept is called tissue borrowing, in which the first movement tested becomes the greatest challenged by other movements. For example, if I move the wrist first in a neurodynamic test, then the nerve in that location would uptake the most tension.
It is also important to mention that when loading the system, accumulation is nonuniform. Depending on where movement comes from, the nerve may get pulled in that direction. For example, near the critical zone at T6, cervical flexion may pull cephalid, whereas knee extension may pull the cord cauded. Other reversal areas include C5-6 and L4-5. Symptoms often show up first at these areas.
When the nerve is stressed available blood flow is affected. A simple increase of 20-30mm Hg pressure can affect blood supply, and generally the longer a stimulus is applied also has an effect. This change can be evident in the various neurodynamic tests.
- If a nerve is entrapped, forces do not dissipate as far, which leads to greater strain at affected site.
- The best resting position for a nerve depends on the injury.