#NerveFact 10 - nerve extensibility is NOT dependent on the connective tissues - why?
This study showed peripheral nerves are more elastic and extensible across joints than between joints.
Widely held belief - resilience and elasticity of peripheral nerves come from the connective tissues so the more epineurium and perineurium, the stiffer and better protected is the nerve (Sunderland 1978).
This resilience was thought to come from the changing fascicular pattern in nerves which produces more connective tissues (epineurium and perineurium) - more fascicles, more protection.
Definitely connective tissues protect nerves but it's more complex.
1. WHAT DID THEY FIND?
Phillips et al (2004) measured peripheral nerve elastivity in vitro by moving the limb and measuring the nerve behaviour across and between the joints (median and sciatic nerves).
The nerves were more elastic across the joints.
Nerves were also removed (ex vitro) and elongated. The nerves behaved the SAME WAY so there was something native about the nerve behaviour ("non-uniform mechanics", Shacklock 1995, 2005).
They also tried to relate it to variations in histology along the course of the nerve - again, more connective tissues, more stiffness.
There was no correlation between the amount of connective tissues and stiffness.
1. Nerve elasticity does not vary with the amount of local connective tissue in the nerve.
2. Nerves have a native capacity to respond to movement.
3. The nerve relationship to musculoskeletal biomechanics is what produced changes - more movement across joints, greater elasticity.
3. IMPLICATIONS FOR HEALTH AND REHABILITATION
A. Mechanically, local nerve responses are highly specific to movement.
B. This flexibility in adaptation fits with other musculoskeletal systems and principles of rehabilitation.
C. Impaired ability of the nervous system to adapt may be a mechanism of pain and impairment and may need treatment.
Phillips J, Smit X, De Zoysa N, Afoke A, Brown R 2004 Peripheral nerves in the rat exhibit localized heterogeneity of tensile properties during limb movement. Journal of Physiology 15 (557) (Pt 3): 879-87
Shacklock M 1995 Neurodynamics. Physiotherapy 81: 9-16
Shacklock M 2005 Clinical neurodynamics: a new system of musculoskeletal treatment. Elsevier, Oxford
Sunderland S 1978 Nerves and nerve injuries. Churchill Livingstone, Edinburgh, UK