Document Detail

Motor and sensory innervation of muscle spindles in the neonatal rat.
MedLine Citation:
PMID:  2966598     Owner:  NLM     Status:  MEDLINE    
Neural and muscular elements of three muscle spindles from the soleus muscles of 4-day-old rats were reconstructed by electron microscopy of skip-serial transverse ultrathin sections. Each spindle contained four encapsulated intrafusal fibers, including a minimum of one bag1, one bag2 and one chain fiber. The fibers were innervated by unmyelinated motor and sensory axons. The primary and secondary afferents approached the spindles as single axons and terminated on the central region of the intrafusal fibers. Single profiles of terminal axons occupied the sites of sensory neuromuscular junctions, similar to adult sensory endings. No morphological features suggested retraction of afferents from 4-day postnatal spindles. Motor axons approached spindles tightly packed in bundles of 5-20 axons and terminated in the juxtaequatorial and polar regions of both bag and chain fibers. Multiple profiles of terminal axons were visible for each intrafusal motor ending. More motor axons innervated 4-day postnatal spindles and a greater number of axon terminals were visible in immature intrafusal motor endings than in adult spindles. The data suggest that postnatal maturation of motor innervation to intrafusal fibers involves the elimination of supernumerary motor nerve inputs. Synapse elimination in the development of the fusimotor system might represent a mechanism whereby individual gamma axons adjust the number of spindles they innervate.
J Kucera; J M Walro; J Reichler
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Anatomy and embryology     Volume:  177     ISSN:  0340-2061     ISO Abbreviation:  Anat. Embryol.     Publication Date:  1988  
Date Detail:
Created Date:  1988-06-02     Completed Date:  1988-06-02     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  7505194     Medline TA:  Anat Embryol (Berl)     Country:  GERMANY, WEST    
Other Details:
Languages:  eng     Pagination:  427-36     Citation Subset:  IM    
Department of Neurology, School of Medicine, Boston University, MA 02118.
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MeSH Terms
Animals, Newborn / anatomy & histology*
Axons / ultrastructure
Microscopy, Electron
Motor Neurons / cytology*,  ultrastructure
Muscle Spindles / cytology*,  ultrastructure
Rats / anatomy & histology*
Grant Support

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