Excitation–contraction coupling in skeletal, cardiac and smooth muscle

37 Excitation–contraction coupling in skeletal, cardiac and smooth muscle





Questions



image How is electrical excitation translated into a contractile event in skeletal muscle?

image How does this process differ in cardiac and smooth muscle types?

image How is the arrangement of contractile fibres in smooth muscle different to that in skeletal and cardiac muscles?


Skeletal muscle


In skeletal muscle, the Ca2+ for contraction comes from the sarcoplasmic reticulum (SR) Ca2+ stores. At the A–I band junction, a regular structure of tubules, known as a triad, is formed that consists of two SR tubules, called terminal cisternae, separated by a deep invagination of the plasma membrane, called a transverse tubule or t-tubule. The release of Ca2+ is triggered by electrical activity in the sarcolemma (muscle plasma membrane) (Fig. 3.37.1C).


image

Fig. 3.37.1 Excitation–contraction coupling. (A) Cardiac muscle; (B) coupling in cardiac muscle; (C) coupling in skeletal muscle.


The t-tubular system ensures that the action potential stimulus for contraction is transmitted rapidly deep within the fibre. The L-type voltage-sensitive Ca2+ channels in the t-tubule system change conformation in response to the depolarization but, rather than admit Ca2+ to the myocyte, these channels are physically coupled to ryanodine-sensitive Ca2+ channels in the SR and stimulate these to open and release Ca2+

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Jun 18, 2016 | Posted by in BIOCHEMISTRY | Comments Off on Excitation–contraction coupling in skeletal, cardiac and smooth muscle

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