This is a Chapter 1 summary of “Clinical Neurodynamics” by Michael Shacklock.
When we first started working with the nervous system, oftentimes we called pathological processes adverse neural tension. The problem with this name was that it left out nervous system physiology; it was mere mechanical concepts. Hence, we call the movement and physiology of the nervous system neurodynamics.
General neurodynamics account for whole body fundamental mechanisms, regardless of region. Specific neurodynamics, on the other hand, applies to particular body regions to account for local anatomical and biomechanical idiosyncrasies.
There are three parts to the neurodynamic structure:
1) The mechanical interface
2) The neural structures
3) The innervated tissues
The mechanical interface is that which is near the nervous system. It consists of materials such as tendon, muscle, bone, intervertebral discs, ligaments, fascia, and blood vessels.
The neural structures are those which make up the nervous system. These structures include the connective tissues that forms the meninges (pia, arachnoid, and dura mater) and peripheral nervous system (mesoneurium, epineurium, epineurium, and endoneurium).
The nervous system has mechanical functions of tension, movement, and compression. It also has physiological functions to include intraneural blood flow, impulse conduction, axonal transport, inflammation, and mechanosensitivity.
The innervated tissues are simply any tissues that are innervated by the nervous system. They provide causal mechanisms for patient complaints, and are able to create nerve motion. When we have neural problems, sometimes the best treatment is to these structures. You must treat everything affected.
The nervous system is capable of performing many mechanical activities:
- Tension – Typically occur at joint areas; the perineurium guards against excessive tension.
- Sliding – Neural structure movement relevant to adjacent tissue. Is able to dissipate tension.
- Longitudinal sliding – Sliding down the tension gradient to allow for tissue borrowing at elongated areas.
- Transverse sliding – Dissipates tension by enabling nerves to take the shortest course between two points when tension is applied. It is also helpful when nerves are subject to sideways pressure by interfaces.
- Compression – The nervous system alters its dimensions and position when forces from the mechanical interface are transmitted to the nervous system. The epineurium protects from excessive compression.
Nerve movement depends on the nerve’s location relative to the joint. If the nerve is on the convex joint side, elongating forces will occur. Conversely, if the nerve is on the concave side, shortening forces will occur.
Despite these forces, nerves may not always move accordingly. The reason for this paradox of sorts is because neural tissue is borrowed from each end of the nerve tract. Therefore, nerves will displace towards the joints; with the end effect being little movement at the midpoint. This phenomenon is called “convergence.”
Interfaces have two actions relative to the nervous system:
- Closing – Reduce distance between the neural tissues and movement complex; creating pressure on the nervous system.
- Opening – Increases distance between neural tissue and interface; reducing nervous system pressure.
These actions can have profound impacts on the nervous system. Take closing for example. It is possible that if a muscle has increased tone or guarding, pressure could increase along a peripheral nerve and create symptoms.
The Nervous System is a Continuum
Any one movement of the nervous system can affect movement at areas further away. Two interesting examples of this occurrence are at the cervical spine and lower back. It has been shown that sagittal neck movement change position and tension in lumbar spinal cord and nerve roots. The other example includes the eyes. When a bilateral straight leg raise is performed, the eyes move inward.
In order to implicate the extent of the nervous system’s involvement requires structural differentiation. The way this action can be achieved is by moving neural structures in the questioned area without moving the musculoskeletal tissues in the same region. An example of this would be symptoms evoked at the wrist with wrist extension that can be altered by changing head position. Because the nervous system is one piece, a pathological process at one area affects the system in its entirety.
Response to Movement
The nervous system moves in a specific order when motion at a joint occurs. First, slack is taken up in early range. Next, sliding occurs in the mid-range, finally, tension builds at end-range.
Slack –> Slide –> Tension
These principles can thus be applied to treatment. A slider involves large movements through the mid-range, whereas a tensioner is performed more at end-range. If someone is incredibly irritable, simply taking up slack in the nervous system can be performed.
Nerves love three things
3) Blood flow
Interestingly enough, peripheral nerve blood flow is regulated by nerves. The major players here are nociceptors and sympathetic fibers. The nociceptive C fibers create vasodilation, which is counterbalanced by the sympathetic nerve’s vascoconstrictive qualities.
Here we shall discuss neurogenic inflammation. This type is when inflammation is produced efferently by the peripheral nervous system; predominately in the c fibers, dorsal root ganglion, and nerve root.
We can test neurogenic inflammation by stimulating the skin. If there are changes in vasodilation capabilities from one side to the other, a potential neurogenic problem may be present. Reduced vasodilation may implicate denervation, whereas increased vasodilation may mean a hypersensitive neural tract.
Neurodynamic sequencing relies on nervous system non-uniformity. There are several big points regarding sequencing movements.
- Movement sequence affects symptom distribution with neurodynamic testing.
- More likely to create symptoms in area moved first.
- Greater nerve strain occurs at the site that is moved first.
- Sliding direction depends on movement order.
- These principles occur anywhere in the nervous system.
Oftentimes when performing neurodynamic testing, resistance will be encountered. This resistance is usually muscle guarding, but it is entirely possible that nerves provide some of this resistance. Regardless of what is causing resistance, this protective mechanism must be respected. This reason is why usually neurodynamic tests are held for only a few seconds and applied slowly.
Applying these concepts to treatment, we can grade how challenging a movement is to the nervous system. This is where we define sliders and tensioners. Sliders are created to produce a sliding movement to improve pain states and nerve excursion. Tensioners, on the other hand, help improve nerve viscoelasticity and physiology.
Another sequencing aspect that can be beneficial is interface testing within neurodynamics. An example of this test would be having a person contract a muscle during a neurodynamic test. This specificity can be useful in detecting hard-to-find processes.
We change the name of this testing to neurodynamics because it accounts for changes in nerve sliding, cross-sectional area and shape, transverse position, axial rotation, viscoelasticity, intraneural blood flow, and mechanosensivity. Calling these tests tension tests only account for one aspect of the nervous system’s capabilities. So to for neural provocation tests, as we are not always trying to provoke symptoms.