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. 2006 Jun;208(6):753-68.
doi: 10.1111/j.1469-7580.2006.00558.x.

An allometric analysis of the number of muscle spindles in mammalian skeletal muscles

R W Banks  1
Affiliations

An allometric analysis of the number of muscle spindles in mammalian skeletal muscles

R W Banks. J Anat. 2006 Jun.

Abstract

An allometric analysis of the number of muscle spindles in relation to muscle mass in mammalian (mouse, rat, guinea-pig, cat, human) skeletal muscles is presented. It is shown that the trend to increasing number as muscle mass increases follows an isometric (length) relationship between species, whereas within a species, at least for the only essentially complete sample (human), the number of spindles scales, on average, with the square root rather than the cube root of muscle mass. An attempt is made to reconcile these apparently discrepant relationships. Use of the widely accepted spindle density (number of spindles g(-1) of muscle) as a measure of relative abundance of spindles in different muscles is shown to be grossly misleading. It is replaced with the residuals of the linear regression of ln spindle number against ln muscle mass. Significant differences in relative spindle abundance as measured by residuals were found between regional groups of muscles: the greatest abundance is in axial muscles, including those concerned with head position, whereas the least is in muscles of the shoulder girdle. No differences were found between large and small muscles operating in parallel, or between antigravity and non-antigravity muscles. For proximal vs. distal muscles, spindles were significantly less abundant in the hand than the arm, but there was no difference between the foot and the leg.

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Figures

Fig. 1
Fig. 1
Scatter plots of logarithmically transformed spindle counts against muscle mass for homologous muscles of three species differing in body mass. The least-squares regression of ln (spindle number) vs. ln (mass) is shown together with its equation. (A) Data from rat, cat and human. (B) Data from guinea-pig, cat and human.
Fig. 2
Fig. 2
Scatter plots of logarithmically transformed spindle counts against muscle mass for the complete sample of human muscles. The least-squares regressions of ln (spindle number) vs. ln (mass) are shown together with their respective equations, as follows: total sample in black; head position and neck muscles in red; shoulder muscles in purple.
Fig. 3
Fig. 3
Distribution of residual values for the sample of human muscles showing their homogeneity.
See this image and copyright information in PMC

References

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