- Latent period: It is the period from the point of stimulus to the point of onset of contraction.
- Contraction period: It is the period between the point of onset of contraction to the point that corresponds to the peak of contraction.
- Relaxation period: It is the period from the peak of contraction to the end of relaxation.
Q.1 What is the cause for Latent Period?
- The latent period is due to a chain of events, including:
- The time taken by the APs to travel from the point of stimulation to the motor endplates.
- Release of acetylcholine, sodium influx, and generation of muscle action potential which leads to contraction.
- Viscosity of the muscle.
- Inertia of the lever system which has to be overcome before contraction can be recorded.
Q.2 What are the factors that determine the
height of the simple muscle curve?
- Strength of stimulus
- Initial length of muscle fibers (preload)
- Type of loading
- Temperature
- Type of muscle fibers in the muscle
- Inertia of the lever system. Greater is the instrumental inertia, lower is the height of the twitch curve.
- Magnification of the lever. The magnification by the lever depends on the ratio of the lengths of the vertical and horizontal arms. This is, of course, fixed in a given lever. A longer horizontal arm will cause greater magnification.