Immediately after the needle is introduced into the
skin, there are evidences of increased capillary
permeability producing rapid local vasodilatation.
The insertion of the needle causes a minute injury to
Injury potentials are generated and can persist and
provide electrical stimulation for days until the
miniature wound heals1.
The injury potentials are known to accelerate healing
by creating galvanotaxis (polarity directed cell
migration) along with a host of other biochemical
The needle, once inserted, can be manipulated by
rotation and pistoning.
It has been found that needle manipulation produces
winding and gathering of collagen around the needle.
Within minutes of needle rotation, this pulling of
collagen toward the needle induces an active cellular
response in connective tissue fibroblasts up to several
centimeters away from the needle2. This transduction
of the mechanical signal into fibroblasts can lead to a
wide variety of cellular and extracellular events leading
to neuromodulation and healing3.
Needle insertion in the skin also releases cortisol,
body’s own steroid1.
Increased local cortisol levels have catabolic effect on
connective tissue stimulating tissue remodelling and
scar tissue breakdown.
Effect on trigger point
Trigger points are small muscular contractures caused
by dysfunctional motor endplates4.
Activation of trigger points may be caused by acute or
chronic muscle overload, activation by other trigger
points, homeostatic imbalances, direct trauma to the
vicinity, radiculopathy, infections etc.
Needling is a widely accepted treatment choice for
deactivation of trigger points.
When the needle is inserted directly to the trigger
point (Deep Dry Needling: DDN), a small muscle
contraction is obtained, which is called Local Twitch
LTRs normalize the chemical environment of active
MTrPs and diminish endplate noise associated with
trigger point instantaneously5.
On the other hand in superficial dry needling (SDN)
only the skin overlying the trigger point is pierced.
This releases the trigger point by reflex inhibition.
Needling produces stimulation of superficial A delta
fibers in the skin6.
This effect may persist for hours after needling due to
the injury potential7.
Stimulation of the sensory afferent A δ activates
enkephalinergic, serotonergic, and noradrenergic
inhibitory systems. Together they work as opioid
mediated analgesia system (OMAS).
This analgesic system involves segmental as well as
suprasegmental pathways8 working through
Substantia Gelatinosa of Rolando (SGR) in the spinal
The following description of needling related pain
modulation is based on Bowsher’s work9.
The segmental modulation
A delta primary afferent receptors project to marginal cells
(M) which carries pinprick sensations in the lateral
The A delta primary afferent receptors also project to
enkephalinergic stalked cells (ST) in the spinal cord,
which inhibits the SGR cells and blocks the
transmission of C pain.
The serotonergic system
The fast pain carrying fibers of lateral spinothalamic tract give
collaterals to peri aqueductal gray matter (PAG) of mid brain.
PAG in turn activates Nucleus RapheMagnus (NRM) of medulla
which stimulates ST cells and inhibit SGR.
The prefrontal cortex can influence the PAG activation via
hypothalamus and activate this descending pain
The noradrenergic system
The nucleus paragigantocellularis (PGC) of medulla
influences locus coeruleus (LC) of pons or similar
noradrenergic brainstem structures which controls firing of
SGR and modulates pain.
This too can be influenced by Pre frontal
cortex- hypothalamus axis.
Diffused noxious inhibitory control
Direct input of A delta generated information to
Reticularis Dorsalis (R) in medulla inhibits pain by its
influence on spinal segment.
1. Gunn C. Chan, Acupuncture and the Peripheral Nervous System A
2. Helene M et al, Connective Tissue Fibroblast Response to Acupuncture: Dose
Dependent Effect of Bidirectional Needle Rotation, J Altern Complement Med.
2007 April ; 13(3): 355–360.
3. Langevin HM et al. Subcutaneous tissue fibroblast cytoskeletal remodeling
induced by acupuncture: Evidence for a mechanotransduction-based
mechanism. J Cell Physiol 2006;207:767-774
4. Simons DG, Hong CZ, Simons LS. Endplate potentials are common to midfiber
myofacial trigger points. Am J Phys Med Rehabil 2002;81(3):212-22.
5. Shah JP, Phillips TM, Danoff JV, Gerber LH. An in vivo microanalytical
technique for measuring the local biochemical milieu of human skeletal
muscle. J Appl Physiol 2005;99:1980-1987.
6. Bowsher D, Physiology and pathophysiology of pain, , aim.bmj.com
September 19, 2012
7. Baldry PE, Superficial Versus Deep Dry Needling, ACUPUNCTURE IN
8. Baldry PE. Acupuncture, Trigger Points and Musculoskeletal Pain. Edinburgh,
UK: Churchill Livingstone, 2005.
9. Bowsher D. Mechanisms of acupuncture. In: Filshie J White A, editors.
Medical Acupuncture - A Western Scientific Approach. Edinburgh: Churchill
Livingstone; 1998. p. 69-82