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The innervation of tandem muscle spindles in the cat neck
Author(s) -
Richmond F. J. R.,
Bakker G. J.,
Bakker D. A.,
Stacey M. J.
Publication year - 1986
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.902450405
Subject(s) - anatomy , sensory system , biology , axon , muscle fibre , sensory receptor , motor unit , free nerve ending , fiber type , neuroscience , skeletal muscle
Patterns of innervation were examined in tandem muscle spindles teased from silver‐stained muscles of the cat neck. Each tandem spindle was composed of two or more encapsulated receptors linked in series by a shared bag 2 fiber. In most tandem spindles, two different types of encapsulation were identified according to differences in their intrafusal fiber content. One type, the b 1 b 2 c unit, contained typical bag 1 , bag 2 , and chain fibers and was structurally similar to single spindles described in other cat muscles. Each b 1 b 2 c unit contained a single primary sensory ending and 1‐6 secondary endings. Fusimotor innervation was supplied by many axons. Some fusimotor axons ended in trail ramifications on bag 2 and chain fibers, others ended in plates on the bag 1 or long chain fiber. The other type of tandem encapsulation, the b 2 c unit, had only bag 2 and chain fibers in its intrafusal fiber bundle. The b 2 c unit was usually supplied by only one sensory axon that ended on the nucleated part of the intrafusal fiber bundle. This single ending had a more variable terminal morphology than the primary ending in b 1 b 2 c units. A few b 2 c units (3/49) were also supplied by a secondary ending. The fusimotor innervation of the b 2 c unit was relatively simple. A single pole of the b 2 c unit was usually supplied by only one to three axons, all ending in trail ramifications. No plate endings were found in b 2 c units. These morphological specializations suggest that b 1 b 2 c and b 2 c units in tandem spindles differ in both their transductive and fusimotor mechanisms. Thus, the tandem spindle is a specialized structure that may provide additional proprioceptive information beyond that available from single muscle spindles.