J. Anim Sci.
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J. Anim Sci. 1974. 39:42-46.
© 1974 American Society of Animal Science
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Fetal and Neonatal Development of Spindle Capsules and Intrafusal Myofibers in the Porcine Sartorius1

H. J. Swatland

University of Wisconsin,2 Madison 53706

Abstract

Muscle spindle development was studied in a series of fetal and neonatal pigs from 60 days gestation to 21 days postnatally. At the sartorius midlength, four spindles were acquired by 99 days gestation and no further increase occurred. The mean number of intrafusal myofibers per spindle increased steadily pre- and postnatally, reaching 10.5 at 21 days. Prenatally, intrafusal myofibers were slightly larger than extrafusal myofibers but, postnatally, this difference was reversed as extrafusal myofibers rapidly hypertrophied. Spindles in the sartorius develop later than those in the biceps brachii.

Footnotes

1 Research was supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison. Muscle Biology Manuscript No. 68. This work was done during the tenure of a Research Fellowship of the Muscular Dystrophy Associations of America.

2 Muscle Biology Laboratory.






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Copyright © 1974 by the American Society of Animal Science.