Skeletal Muscle- Excitation

Prof. K. Sivapalan

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Muscle Types

• Skeletal muscle- attached to skeleton

• Striated muscle- striations under light microscope. [40% of the body, other types 10 %].

• Smooth muscles- no striations- many subtypes.

• Cardiac muscle- found in heart, striated but different from skeletal muscles

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Muscle Structure• Skeletal muscles connect two structures (bones)

through tendons or directly.

• Muscle cell is known as muscle fiber, 10-80 µ in diameter, extending from one end to the other end of the muscle.

• It is multinucleated, rich in mitochondria, full of myofibrils.

• Innervated by one axon at its middle through the motor-end plate.

• Sarcolemma is excitable as nerves. [RMP -90]

• Sarcoplasmic reticulum forms a tubular system that transmits the action potential into the sarcoplasm.

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Skeletal Muscle

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Myofibrils

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Myofibrils

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Motor End Plate

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Stimulation of the Muscle

• Action potential reaches the motor end plate

• Calcium entry into axonal terminal

• Release of acetyl choline

• Ligand gated channels- increase Na+ entry- threshold level

• Action potential spreads along the sarcolemma

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Sarcotubular System

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Excitation – Contraction Coupling

• Action potentials spread along the Transverse tubular system.

• The terminal cisterns release Ca++

• Calcium ions facilitate binding of actin and myosin.

• Calcium is transported back into sarcoplamic reticulum and back into terminal cistern.

• Removal of calcium results in relaxationJune 2013