PMID: 5919565Apr 1, 1966

An electrophysiological study of chelonian skeletal muscle

The Journal of Physiology
L Levine


1. Membrane properties of fibres of the retractor capitis muscles of the tortoise, Testudo graeca, and of the terrapin, Pseudemys elegans scripta, have been investigated with electrophysiological techniques. The features studied were qualitatively and quantitatively similar in both.2. Fibres are electrically excitable and many extend through 90% of the length of the muscle. In the tortoise muscle conduction velocity was 0.8 m/sec in hibernating animals, and 1.3 m/sec in active animals.3. Resting potentials averaged -80 mV and action potentials ca. 115 mV. The critical membrane potential in the tortoise was -38.5 mV. Neurally initiated action potentials, recorded at the end-plate, were reduced in amplitude by 14 mV in both forms, and the end-plate ;step' from which the action potential arose was -39 mV. Resting potentials at the end-plate were not different from those recorded at non-junctional sites. The rise time of the action potential at non-junctional sites was 1.1 msec, and the time for repolarization to 50% was 2 msec in both forms. In hibernating tortoises the rise time was three times longer and the fall time doubled.4. The average calculated fibre diameter was ca. 50 mu in the tortoise muscle, and membrane constants we...Continue Reading

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