Question

Describe the process of excitation-contraction coupling in a skeletal muscle fiber, starting at the very beginning and working your way to the end of the process. Make sure you discuss all relevant steps in the correct order.

Answer 1

Each muscle fiber is made up of many myofibrils which contains the sarcomeres which are the basic contractile units of muscle.

Sarcomeres have thin filaments called actin and thick filaments called myosin which allow contraction and relaxation.

The plasmamembrane of muscle fibres is called sarcolemma and cytoplasm is called sarcoplasm.

Steps in the process of excitation-contraction coupling in a skeletal muscle fiber

1.somatic motor neuron releases neurotransmitter Ach(acetylcholine).

2.Ach released from the axon terminal binds to the Ach receptors on the sarcolemma.

3.Ion channels open and positively charged sodium ions rush across membrane.

4.An action potential is generated which travels down the sarcolemma and enters T tubules . T tubules are extensions of the sarcolemma.

5.calcium is released from the sarcoplasmic reticulum due to change in voltage.

6.calciuim binds to troponin on the thin filament.due to this troponin moves and consequently tropomyosin moves. Both troponin and tropomyosin are proteins and lies with in the groove between actin filaments.

7.cross bridges are formed between actin and myosin.myosin heads pulls the thin filaments towards the M line (contraction occurs )

8.acetylcholinesterase removes Ach from the synaptic cleft.

9.calcium is transported back into the sarcoplasmic reticulum.

10.Tropomysosin binds to the active sites on actin which causes the cross bridge to detach.