The Spatial and Segmental Innervation of Somatic Acupoint — A Study of Canine Shen-Shu Point (BL-23)

Abstract

Although an acupuncture needle penetrates the skin, subcutaneous tissue, and underlying muscle, the most effective locus for the somatic acupoint on the needle path is not well established. We therefore investigated the sensory innervations of tissues in the needle path of the canine Shen-Shu point and evaluated their roles in initiating an acupunctural signal. Horseradish peroxidase solution was injected at all three levels within the acupoint. Only a few peroxidase-positive neurons were observed in the L1 dorsal root ganglion following intradermal injection. Following subcutaneous injection, peroxidase-labeled neurons were detected extending from spinal levels T10 to L2, with maximal labeling at T12 (46.3%). Approximately 95% of positive neurons were at spinal levels T11, T12, T13, and L1. As a result of an intramuscular injection, labeled neurons were observed at spinal levels T12 to L3, with most labeling occurring at L1 (39.9%). Approximately 95% of positive neurons were at spinal levels T13, L1, and L2. The results suggest that most afferent terminals are in the subcutaneous tissue rather than the muscular tissue, with an approximate ratio of 3.75:1. The data provide solid evidence that sensory innervation to a somatic acupoint is confined to a spinal segment and spatially organized, and we speculate that to cause a maximum effect, the centripetally transmitted signal from needling a somatic acupoint is spatio-segmental and divergently amplified.

A Neurosegmental Perspective of the Classical Back Shu Points

“…1-3 These points are located at T-10, T-11, and T-12 segments, which are not the correspondent sympathetic nervous system innervations levels for the actual organs. [5][6][7]13 BL 19 is outside of the gallbladder's sympathetic innervation level, and spleen (BL 20) and stomach (BL 21) are described over the adrenals' segmental innervation levels (T-11 and T-12). The actual sympathetic roots are T-5 to T-10 for stomach, T-6 to T-10 for spleen, and from T-6 to T-9 for gallbladder, as described in Table 1.…”

“…18 According to modern neuroanatomy, the sympathetic trunk and its rami are structured in a way in which a single organ is nourished by several levels (metameres). [5][6][7]13,19 The traditional model currently used for BSP is not consistent with the known sympathetic nervous system anatomy because the TCM model is organized so that 1 point treats specifically 1 organ. As shown in Table 1, there is a complete correspondence between BSP, dermatomes, sympathetic system, and parasympathetic system.…”

“…7 According to their research, the interconnections may reach up to 5 segments at the subcutaneous depth. However, at the muscle level, needle stimulation reaches up to 2 segments.…”

“…This neuroanatomical architecture corroborates the hypothesis that acupuncture stimulation on 1 level will affect 1, 2, or more spinal levels. 7,20 Further research and clinical studies need to be performed to confirm how many levels are reached in each site of needling.…”

“…Comparison between the BSP, the neuroanatomic pathways, and their nervous system functions shows many similarities with TCM concepts but also with a few peculiarities explained below. [5][6][7] only the BSP of the 5 Yin organs (Lung, Heart, Liver, Spleen, and Kidney) are described with slightly different locations from those currently used. 1,[8][9][10] According to historical references, Dr Huatuo (110-207 ad) 11 described the BSP locations to be about 1 cun lateral to the midline of the spine.…”