Compare and contrast by stating five differences (indicated below) between the e

Question

Compare and contrast by stating five differences (indicated below) between the excitation-contraction coupling (ECC) between SKELETAL and SINGLE UNIT SMOOTH MUSCLE.

Compare how each relates following criteria (1-5).

1) discuss how the sarcolemma is activated to generate an action potential

2) discuss how calcium increases in the sarcoplasm

3) discuss how myosin globular heads are activated

4) discuss how sliding of thin filaments occurs

5) compare how the detachment of myosin globular heads occur

Explanation / Answer

DIFFERENCE BETWEEN SKELETAL MUSCLE AND SINGLE UNIT SMOOTH MUSCLE IN EXCITATION- CONTRACTION COUPLING PROCESS ARE FOLLOWING :

1. The depolarisation of sarcolemma with the reversal of of flow of ions-- more Na+ towards interior than K+ pass out, generates the action potential in the skeletal muscle. While in single unit smooth muscle it occurs via activation of pacemaker cells connect in control with autonomic nervous system.

2. In skeletal muscle fibre the action potential is transmitted internally through T- tubules to sarcoplasmic reticulum, the latter releases Ca++ in the sarcoplasm. It is also not quite differ in smooth muscle where the stimulation of muscle increase the Ca++ concentration in the sarcoplasm.

3. Calcium ion creates ATPase activity over myosin filaments that activates myosin heads. But in case of smooth muscle myosin heads are activated when light chain of myosin are phosphorylated by myosin-light chain kinase(MLCK).

4. The energy in the form of ATP along with Mg++ is required in moving active sites of actin filaments (thin) over lateral knobs of myosin in skeletal muscle while in the single unit smooth muscle some special structures ( dense bodies and imtermediates filaments) by attached together assist in thin actin filaments.

5. In skeletal muscle, during relaxation Ca++ are picked up from sarcoplasm actively by sarcoplasmic reticulum cause ATPase enzyme to inactivate and myosin head detached. While in smooth muscle myosin-light chain phosphatase countered with the activity of MLCK and dephosphorylate the myosin head, that promote the myosin head to detach.

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