HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 101/4/1722    most recent 90976.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Cao, D.-Y. Articles by Khalsa, P. S. Search for Related Content PubMed PubMed Citation Articles by Cao, D.-Y. Articles by Khalsa, P. S.

Position Sensitivity of Feline Paraspinal Muscle Spindles to Vertebral Movement in the Lumbar Spine

¹Palmer College of Chiropractic, Palmer Center for Chiropractic Research, Davenport, Iowa; and ²Department of Biomedical Engineering, State University of New York, Stony Brook, New York

Submitted 28 August 2008; accepted in final form 15 January 2009

Muscle spindles contribute to sensorimotor control by supplying feedback regarding muscle length and consequently information about joint position. While substantial study has been devoted to determining the position sensitivity of spindles in limb muscles, there appears to be no data on their sensitivity in the low back. We determined the relationship between lumbar paraspinal muscle spindle discharge and paraspinal muscle lengthening estimated from controlled cranialward movement of the L₆ vertebra in anesthetized cats. Ramp (0.4 mm/s) and hold displacements (0.2, 0.4, 0.6, 0.8, and 1.2 mm for 2.5 s) were applied at the L₆ spinous process. Position sensitivity was defined as the slope of the relationship between the estimated increase in muscle length and mean instantaneous frequency at each length. To enable comparisons with appendicular muscle spindles where joint angle was measured, we also calculated sensitivity in terms of the L₆ and L₇ intervertebral flexion angle (IVA). This angle was estimated from measurements of facet joint capsule strain (FJC) based on a previously established relationship between IVA and FJC strain in the cat lumbar vertebral column during lumbar flexion. Single-unit recordings were obtained from 12 muscle spindle afferents. Longissimus and multifidus muscles contained the receptive field of 10 and 2 afferents, respectively. Mean position sensitivity was 16.3 imp·s^–1·mm^–1 [10.6–22.1, 95% confidence interval (CI), P < 0.001]. Mean angular sensitivity was 5.2 imp·s^–1·°^–1 (2.6–8.0, P < 0.003). These slope estimates were more than 3.5 times greater compared with appendicular muscle spindles, and their CIs did not contain previous slope estimates for the sensitivity of appendicular spindles from the literature. Potential reasons for and the significance of the apparently high position sensitivity in the lumbar spine are discussed.