Flexion and Extension : Studies Employing Muscles of the Shank in Amphibians

Abstract

Tibialis anticus and peronaeus longus of the frog have been examined
by optical and electron microscopy. Sodium and potassium concentrations
of these muscles have been determined. Double myograms have been used
to compare physiological and pharmacological properties of flexor and
extensor and to demonstrate various patterns of convulsion and their
modification by depressants. Contractures have been investigated in
the isolated organ bath. Depolarizing agents have been used to compare
the proportions of slow fibres in the gastrocnemius of frogs and toads.

Tibialis anticus, a flexor, has been shown to be heterogenous,
consisting of twitch and slow fibres, and peronaeus longus to be
homogenous, containing only twitch fibres. The twitch fibres of the
flexor are shown to be fast compared with the twitch fibres of the
extensor and their resting potentials, as deduced from potassium
concentrations, are found to differ, Evidence is collated to
evince the principle that a flexor is heterogenous to effect the
functions of rapid withdrawal and of maintaining that withdrawal,
whereas an extensor is homogenous since it merely exerts a thrust.
Analogies between amphibian and mammalian muscle fibres are
discussed.

Date of Award	1973
Original language	English