Question

Compare and contrast the function of calcium in skeletal and smooth muscle contraction. In your answer, make sure to address the following questions:

•Where does calcium come from and how does it get into the cell?

•What triggers the entry of calcium?

•How does calcium couple excitation (stimulation of the muscle cell) with contraction?

•How is calcium removed for relaxation?

Answer 1

Smooth muscles.

In smooth muscles, calcium ions for contraction comes from extracellular fluid.

Calcium, which enters the sarcoplasm from extracellular fluid combines with a protein called cadmodulin and forms calcium- cadmodulin complex. This complex activates myosin ATPase and contraction occur.

Relaxation of muscle occur due to dissociation of calcium-cadmodulin complex.

Skeletal muscles-

c​​​​​alcium ions are stored in cisternae of sarcoplasmic reticulum.

Action potential spreads over sarcolemma and also into muscle fibre. When action potential reaches cisternae of L tubules , these cisternae are excited. Calcium stored in cisternae are released into sarcoplasm. The calcium ions from sarcoplasm moves towards the actin filaments to produce the contraction.

During relaxation, calcium ions are pumped back to L tubules.