P01.25. Classification of L6 muscle spindle afferents in the anesthesized cat

  • W Reed
  • J Pickar
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Keywords

Paraspinal Muscle Receptive Ending Multifidus Muscle Intrafusal Fiber Lumbar Muscle 

Purpose

Patients with low back pain demonstrate proprioceptive difficulties including spinal repositioning errors and impaired lumbosacral proprioceptive acuity. Few data are available regarding proprioceptive properties of muscle spindles in the low back. Muscle spindle afferents can originate from 2 types of receptive endings which terminate and respond to mechanical changes in 3 types of intrafusal fibers. Receptive endings may be primary or secondary. They terminate on dynamic bag (b1) static bag (b2) and/or chain (c) intrafusal fibers. We sought to classify lumbar paraspinal muscle spindle afferents based upon their receptive endings and intrafusal terminations. Classification was based on their responses to ramp and hold vertebral movement before and after intrafusal activation using succinylcholine (SCH, 100-300ug/kg.ia). Afferents terminating in primary endings are especially responsive to the dynamic ramp stimulus. During intrafusal activation, afferents terminating on b1 fibers further increase their discharge to the dynamic ramp whereas those terminating on b2 fibers increase their static resting discharge.

Methods

Electrophysiological recordings from spindle afferents (n=195) were obtained from L6 dorsal root filaments with receptive fields in the L6 longissimus and multifidus muscles in an anesthetized cat preparation. Controlled vertebral actuations that stretched the paraspinal muscles were applied to the L6 spinous process in a dorsal-ventralward direction [1.5mm (n=120), 1.6mm (n=21), or 1.7mm (n=54) using a feedback motor system. Instantaneous discharge frequency was averaged and compared over three ramp cycles pre- and post-SCH injection.

Results

Table 1

 

LONGISSIMUS

MULTIFIDUS

 

b1c

b2c

b1b2

b1c

b2c

b1b2

Primary

0

100

46

0

19

10

Secondary

0

0

0

0

4

1

Intermediate

0

5

0

0

1

0

Conclusion

Almost all lumbar muscle spindle afferents showed static sensitivity responding as primary endings terminating on b2 fibers. Approximately 1/3 of the afferents responded as primary endings terminating on both b1 and b2 fibers. No endings were exclusively sensitive to the dynamic ramp stimulus.

Copyright information

© Reed and Pickar; licensee BioMed Central Ltd. 2012

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Authors and Affiliations

  • W Reed
    • 1
  • J Pickar
    • 1
  1. 1.Palmer College of ChiropracticDavenportUSA

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