Untersuchungen an isolierten Muskelspindeln der Ratte nach Cholinesterasedarstellung und Sudanschwarz-Färbung

Summary

After staining of the motor nerve endings with a cholinesterase technique and of nerve and muscle fibers with Sudanschwarz B, single muscle spindles were isolated from lumbrical muscles of rats and examined by means of light microscopy.

Two types of intrafusal muscle fibres were found: a) pale ones corresponding to nuclear bag fibres and b) dark ones corresponding to nuclear chain fibres.

On both types of muscle fibres distinct motor end plates were observed; two types of endplates can be distinguished: a) Larger ones consisting of circular subunits in loose arrangement; they occur on pale muscle fibres only. Their number per muscle fibre pole may amount up to three, b) Smaller ones with more compact arrangement of their subunits occurring on dark fibres only. Their number per muscle fibre pole never exceeds one.

Besides these distinct endplates with more mid-polar positions, a second kind of motor nerve ending is to be found in the juxtaequatorial region of every spindle pole: the multiterminal motor ending. These endings are located predominantly on pale intrafusal muscle fibres.

An often very thin γ-fibre leads to every juxtaequatorial region, looses its myelin sheath and divides into several thin branches; these non-myelinated axon-branches may be observed over rather long distances, finally forming the multiterminal endings.

Every distinct motor endplate receives its own — usually somewhat thicker—γ-fibre which looses its myelin sheath immediately before its termination at the endplate. The terminal parts of these fibres show no branching.

The dark intrafusal muscle fibres receiving one motor end plate only, correspond to those intrafusal fibres of the rat which, according to other authors, show properties of twitch fibres. The pale fibres receiving multiterminal endings and multiple motor endplates, correspond to fibres which show some criteria of slow fibres.

Zusammenfassung

An isolierten Muskelspindeln aus Lumbrical-Muskeln der Ratte, deren motorische Endigungen mit einer Cholinesterase-Technik dargestellt, deren Nerven- und Muskelfasern mit Sudanschwarz gefärbt worden waren, wurden lichtmikroskopisch folgende Befunde erhoben: Es gibt 2 Typen intrafusaler Muskelfasern: a) helle, den „nuclear bag fibres“ entsprechende, b) dunkle, den „nuclear chain fibres“ entsprechende.

An beiden Fasertypen kommen distinkte motorische Endplatten vor, die gleichfalls in zwei Typen differenzierbar sind: a) Größere, aus locker gefügten, runden Untereinheiten bestehende; diese befinden sich nur an den hellen Fasern. Ihre Anzahl an jedem Polabschnitt kann bis zu drei betragen. b) Kleinere, kompakter gebaute motorische Endplatten; diese liegen nur an den dunklen intrafusalen Fasern, je Faserpol maximal eine.

Außer den mehr in Polmitte liegenden distinkten Endplatten sieht man in den paraäquatorialen Polabschnitten regelmäßig eine zweite Art intrafusaler motorischer Nervenendigungen: die multiterminalen motorischen Endigungen. Diese an jedem Spindelpol sichtbaren Endigungen sind vorwiegend an den hellen intrafusalen Fasern lokalisiert.