Title: Skeletal muscle physiology | BJA Education | Oxford Academic
Headings: Skeletal muscle physiology
Skeletal muscle physiology
Published:
Subject
Issue Section:
Key points
Electrical events in muscle contraction
Excitation-contraction coupling
Contractile structures
Force transmission
Determinants of force of contraction
Summation
Recruitment
Energy for contraction
Muscle fibre-types
Further reading

Content: Skeletal muscle sarcolemma is characterized by invaginations called transverse- or t-tubules that run perpendicular to the surface of the cell deep into its body. By passing down the t-tubular membrane, the action potential is carried to the structures responsible for transducing an electrical into a chemical signal that will trigger activation of the contractile elements. Excitation-contraction coupling
This term encompasses the processes by which the surface membrane action potential leads to interaction of the intracellular contractile elements. The t-tubular membrane contains the highest density in the body of binding sites for dihydropyridine compounds, such as nifedipine. This finding was initially assumed to suggest that arrival of the action potential in the t-tubules opened voltage-gated Ca 2+ channels. We now know that, although the t-tubular dihydropyridine receptors show marked amino acid homology with L-type voltage gated Ca 2+ channels of other tissues, they do not function as Ca 2+ channels. Their role in skeletal muscle is that of voltage sensors. When the action potential arrives in the t-tubule, the change in membrane potential leads to a conformational change in the α-subunit of the dihydropyridine receptor. This subunit consists of four transmembrane domains each of six segments ( Fig. 1 ).