AN HRP STUDY OF LOCALIZATION AND TOPOGRAPHICAL MAPPING OF THE MOTONEURONS SUPPLYING THE RAT SERRATUS ANTERIOR MUSCLE

Document Type : Regular Paper

Authors

1 Department of Anatomy, Cellular & Molecular Research Center, Neuroscience Division, Iran University of Medical Sciences, Hemmat Express Way, Tehran, I. R. of Iran

2 Department of Oral Anatomy, School of Dentistry, University of Tokushima, Tokushima, Japan

Abstract

Shoulder movements are a complex motor act, controlled by many muscles attached to the
scapula and the vertebral column. These muscles are innervating by motoneurons (Mns) located in the
ventral horn of the spinal cord. Motoneurons of the ventral horn are arranged such that several groups of
Mns can be distinguished in a transverse section through the spinal cord. The anatomical or functional
implication of these groups is still unknown. The present research was designed to determine the
location and topographical mapping of Mns to the rat serratus anterior (SA) muscle.
Thirty young adult male rats weighing 180-250g were used in this study. The location and
distribution of the Mns in the rat cervical spinal cord to the serratus anterior (SA) muscle of the rat have
been studied using horseradish peroxidase (HRP) intramuscular injection and the application of a HRP
nerve dipping method to the long thoracic nerve. Following the intramuscular injection of HRP and also
a nerve dipping for the long thoracic nerve, labeled motoneurons were identified ipsilaterally to the side
of HRP application forming two main cell columns extended rostrocaudally in the ventral horn of both
sides. The column G5 extended longitudinally from the caudal half of the fifth (C5) to the rostral half of
the seventh (C7) cervical segments in group five. The column G7, located mainly in the rostral half of
the C7 in group seven. The serratus anterior labeled motoneurons showed a rostrocaudal somatotopic
distribution in each of the columns G5 and G7.
These results suggest that there is a specific functional role for motoneurons, and also that
motoneurons are arranged in the form of a motor pool with a musculotopic pattern of distribution
corresponding to the embryonic origin and anatomical position of the muscles they innervate to.

Keywords

Iranian Journal of Science
Volume 29, Issue 1 - Serial Number 1
January and February 2005
Pages 9-17

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