Observations on the fusimotor fibres of the tibialis posterior muscle of the cat

SUMMARY1. The distribution of fusimotor axons to bag1, bag2 and chain muscle fibres in cat tenuissimus spindles has been studied using a modification of the glycogen-depletion technique of Edstr6m & Kugelberg (1968). Single fusimotor axons were stimulated intermittently at 40-100/sec for long periods (30-90 sec) during blood occlusion. Portions of muscle containing the activated spindles were quick-frozen, fixed in absolute ethanol during freeze-substitution, and then embedded in paraffin wax. Serial transverse sections were stained for glycogen using the periodic acid-Schiff method, and examined for depletion.2. Dynamic y axons (i.e. those that increase the dynamic index of primary-ending responses to ramp stretches of large amplitude) depleted bag1 fibres almost exclusively.3. Static y axons (i.e. those that reduce or abolish the dynamic index) depleted both bag and chain fibres. Bag1 and bag2 fibres were depleted about equally. 4. A single static y axon may activate both bag and chain fibres in one spindle (the most common pattern), chain fibres only in another, and bag fibres only in a third spindle.5. Static y axons with conduction velocities less than 25 m/sec also had a non-selective distribution, but no depletion was observed in bag2 fibres.6. The zones of depletion produced by dynamic y axrons were distributed more or less equally in the intra-and extracapsular parts of spindle poles, whereas those produced by static y axons were mainly intracapsular.7. The results are compared with the glycogen-depletion studies of Brown & Butler (1973 and our own study of the distribution of

Section: Methodsmentioning

confidence: 99%

“…2). As against this the action of a single fusimotor axon has so far been found to be the same on all the spindles it supplies (Crowe & Matthews, 1964;Brown et al 1965;Bessou et al 1966). …”

Section: Distribution Of Fusimotor Axonsmentioning

confidence: 99%

Distribution of fusimotor axons to intrafusal muscle fibres in cat tenuissimus spindles as determined by the glycogen‐depletion method.

Barker¹,

Emonet-Dénand²,

Harker³

et al. 1976

“…In other spindles these same axons were supplying either only chain fibres or both chain and bag fibres. Since one axon exerts the same kind of functional action on all the muscle spindles it innervates (Crowe & Matthews, 1964;Brown, Crowe & Matthews, 1965;Bessou, Laporte & Page's, 1966), it may be asserted that static effects exerted by a single y axon are not related to the distribution pattern of the axon on the various types of intrafusal muscle fibres.…”

Section: Considerations Of the Functional Implications Of Fusimotor Amentioning

confidence: 99%

Cinematographic analysis of contractile events produced in intrafusal muscle fibres by stimulation of static and dynamic fusimotor axons.

Bessou¹,

Pagès²

1975

SUMMARY1. Muscle spindles with an intact blood supply and uninterrupted connexions with ventral and dorsal spinal roots (Bessou & Pages, 1967 have been prepared in cat's tenuissimus muscles with the aim of cinephotographically recording intrafusal movements induced by the stimulation ofsingle static or dynamic y axons; the time course ofthese movements and the morphological kind of activated intrafusal muscle fibres have been established.2. Displacements of spindle guiding marks in the equatorial region elicited by stimulating single static y axons are 4-20 times greater in amplitude than the ones elicited by stimulating dynamic y axons at the same frequency.3. The dynamic y axons induced a contraction only in nuclear bag fibres which, in addition, never received any static y innervation. The static y axons evoked contractions either in nuclear bag fibres alone, or in nuclear chain fibres alone, or in both types of intrafusal fibres. Two thirds of static y axons supplied nuclear bag fibres. For various reasons, one half only of static y axons innervating nuclear bag fibres could be shown to simultaneously innervate nuclear chain fibres. Consequently, about one third of static y axons supplied both nuclear bag fibres and nuclear chain fibres, but it is highly probable that this latter figure is an underestimate. One third of static y axons produced contraction in nuclear chain fibres only. In this work, the distribution of fusimotor axons has been established in only one muscle spindle of the cluster of muscle spindles that each fusimotor axon is generally innervating.4. Generally speaking, a static y axon elicits contraction of several intrafusal fibres whereas a dynamic y axon innervates only one intrafusal fibre and frequently only one pole of the fibre. P. BESSOU AND B. PAGES 5. One third of static y axons evoked contractions in nuclear chain fibres that seemed to involve the whole pole. The other static y axons and all dynamic y axons produced, in the intrafusal fibres that they supplied, one or several foci of localized contractions.6. The nuclear chain fibres contract and relax faster than nuclear bag fibres. The contractions of nuclear bag fibres supplied by static y axons are stronger and faster than those of nuclear bag fibres innervated by dynamic y axons. Nearly all nuclear bag fibres innervated by static y axons, like the nuclear chain fibres, show transient contractions at each pulse of a stimulation at low frequency (2-20/sec).7. The results are discussed taking into account the available anatomical and physiological data on the muscle spindle. Their consequences with regard to intrafusal working are briefly considered.

“…There is evidence (e.g. Bessou et al 1965;Brown, Crowe & Matthews, 1965) that y dynamic fibres and /3 dynamic fibres can successfully innervate the same spindle. It seems possible then that the extra /3 motor innervation provided to the spindles as a result of reinnervation will persist even if the y fibres eventually return to the spindles as well.…”

Section: /3 Fibresmentioning

confidence: 99%

Regeneration of afferent and efferent fibres to muscle spindles after nerve injury in adults cats.

Brown¹,

Butler²

1976

SUMMARY1. The nerves to cat peroneus longus and tenuissimus muscles were either cut or crushed close to the muscle and the afferent and efferent nerve supply to the muscle spindles was studied electrophysiologically between 2 and 32 weeks later.2. Recovery was more rapid and complete after crush than section for both afferent and efferent fibres. After recovery from either procedure normal primary and secondary afferents and static and dynamic y efferent fibres were found.