Related Experiment Video
Updated: Aug 1, 2026

Isolating Myofibrils from Skeletal Muscle Biopsies and Determining Contractile Function with a Nano-Newton Resolution Force Transducer
Published on: May 7, 2020
Contraction time, histochemical type, and terminal cisternae volume of rat motor units
Abstract:
Isometric contraction time (Tc) of 19 fast and slow rat motor units in the soleus and the tibialis anterior muscles was measured. The motor unit fibers subsequently marked by glycogen depletion were histochemically fiber typed as well as analyzed ultrastructurally with respect to volume of the sarcoplasmic reticulum terminal cisternae. The volume density of terminal cisternae (VVTC) was inversely related to Tc over the whole range of motor units, irrespective of type of muscle. The continuous variations in VVTC are concluded to match the extrinsic control of time course of contraction, and fusion frequency of the motor unit to match the frequency characteristics of the individual motoneurons. The volume density dependence of terminal cisternae function would result in an indirect coupling between amount and rate of calcium release and rate of calcium recaptured. VVTC and Tc were the same for some tibialis anterior and soleus motor units in spite of the different types of myosin, indicating that the type 1 and type 2 myosins have specific structural differences in fast as compared with slow muscles.
Related Concept Videos
Actin and Myosin in Muscle Contraction
Excitation-Contraction Coupling in Skeletal Muscles
When an action potential...
Relaxation of Skeletal Muscles
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated sodium channels. Sodium ions enter the cell, further depolarizing the presynaptic membrane. This depolarization causes voltage-gated calcium channels to open.
Motor Unit Stimulation
The latent period of contraction marks the onset of excitation-contraction coupling, when the action potential propagates across the sarcolemma, preparing the muscle fibers for contraction. As the fibers enter the contraction phase, the...
Specialized Characteristics of Cardiac Muscles
Cardiac muscle cells are smaller than skeletal muscles, averaging 10–20 mm in diameter and 50–100 mm in length. However, they have large energy demands for continuous contraction and relaxation. This energy is almost exclusively derived from aerobic metabolism of energy reserves in...
Smooth Muscle Contraction
The onset of contraction is triggered by an increase in calcium ions within the sarcoplasm, similar to the process in striated muscle. However, smooth muscles have a relatively smaller reservoir of the sarcoplasmic...

