Journal of Neurophysiology, Vol 52, Issue 6 1131-1139, Copyright © 1984 by APS
Active force and sensory response of single isolated cat muscle spindles in vitro
Y. Fukami
Active tetanic tension developed by stimulation of a nerve innervating
single isolated muscle spindles of the cat was measured. The maximum
tetanic force varied among spindles, ranging from 2.3 to 8.5 mg. For four
spindles, the maximum tetanic force was converted into the force per unit
cross-sectional area of nuclear chain and nuclear bag fibers. The results
are discussed in terms of structural and functional complexities of the
intrafusal fibers. The length-tension diagram of single isolated spindles
showed maximum tetanic tension occurring at a spindle length longer than
1o, which was defined as the length beyond which passive tension starts to
develop. This result, which appears to be different from the corresponding
diagram for extrafusal muscle, is discussed in relation to the existing
reports on the mechanical properties of intrafusal fibers. Spindle sensory
response vs. tetanic tension was analyzed for single isolated spindles with
two independent nerve supplies, one containing sensory and the other
containing fusimotor axons. The results suggest that the static discharge
rate of sensory endings may be linearly related, within the range examined,
to the tetanic plateau tension of intrafusal fibers.
