The distribution of static gamma‐axons in the tenuissimus muscle of the cat.

Abstract

SUMMARY1. The distribution of static y-axons within and among muscle spindles of the tenuissimus muscle has been studied in the anaesthetized cat, on the basis of the effects on the responses of primary endings when bag2 or chain fibres or both are activated by static y-stimulation.2. Locations of spindles were marked for subsequent histological analysis using teased, silver-impregnated preparations.3. Static effects were classified into: (i) biassing; (ii) driving; or (iii) indeterminate categories.4. Critical correlations established that the biassing type was produced by bag2 activity, either alone or in combination with chain fibres, whereas the driving type was produced by chain fibres active alone. Indirect evidence suggested that indeterminate effects were produced by bag2 and chain fibres active together.5. The static y-axons showed some differential distribution according to their conduction velocities: faster-conducting axons were likely to be more widely distributed among spindles but less likely to innervate chain fibres alone than were more slowly conducting axons.6. The results are discussed in terms of their possible functional and developmental significance.

Comparison of skeleto‐fusimotor innervation in cat peroneus brevis and peroneus tertius muscles.

“…A fiS-axon commonly supplies only one chain fibre pole, the longest, among all the several chain fibres present in a spindle, but rarely two, as shown by histophysiological studies (Harker, Jami, Laporte & Petit, 1977;Jami, Lan-Couton, Malmgren & Petit, 1978, 1979Banks, 1991) and by tracing of the intrafusal branch of fl-axons (:Kucera, 1984). Thus, in a population of spindles, the total number of chain fibre poles which are supp] ie(d by yS-axons largely exceeds that of chain fibre poles supplied by ,8S-axons.…”

Analysis of Motor Fibers in the Communicating Branch between the Cervical Nerves and the Spinal Accessory Nerve to Innervate Trapezius in the Rat

“…The g motor fibers distribute on the polar portions of both bag and chain fibers (Barker et al, 1978;Kucera, 1980;Banks, 1991;Maier, 1992Maier, , 1997; Emonet-Dé nand et al, 1998, 2001). Our findings that the motor elements from the communicating branch were distributed on the polar regions of the intrafusal fibers (both bag and chain fiber) definitively.…”

Primary and secondary afferent discharges from the same spindle during chain fibre contraction in cat tenuissimus muscle

“…In the present experimental conditions (de-efferented muscle spindles activated by only one static y-axon) it is likely that in many instances only one pole contracted since y,-axons supplying both poles are much less frequent than ys-axons supplying only one pole (Boyd & Gladden, 1985;Banks, 1991) and that action potentials generated in the membrane of one pole apparently do not propagate to the other pole through the equatorial region (Bessou & Laporte, 1965b). Consequently, the contraction of one pole must stretch the passive opposite pole as well as the equatorial region on which the primary endings lie.…”

“…In six of the ten cases where recordings were made of the discharges from two secondary endings lying in the same spindle (in addition to that of the primary ending), one secondary was excited distinctly more than the other when the y,-axon was stimulated at 30 stimuli/s (Figs 3, 4 and 6). Tenuissimus spindles with two secondary endings on either side of the primary endings are much more common than spindles with two secondary endings on the same side (Banks et al 1982;Banks, 1991). Thus, it is quite possible that one of the secondary endings was activated more than the other because it was situated on the side of the contracting pole (most y-axons supply one pole only; Boyd & Gladden, 1985;Banks, 1991) and that the secondary ending situated on the opposite pole was less activated because the equatorial region attenuated the force generated by the contracting pole.…”