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Steps in Skeletal Muscle Contraction and its related terms

1st step of skeletal muscle contraction

An action potential travels along a motor neuron toward a skeletal muscle. Their point of connection is called a neuromuscular junction.

2nd step of skeletal muscle contraction

At the junction, acetylcholine vesicles are released.

3rd step of skeletal muscle contraction

Acetylcholine binds to its receptor on the sarcolemme causing Na+ influx into the muscle fiber, generating an action potential within the muscle fiber.

4th step of skeletal muscle contraction

The action potential travels through the T-tubules, allowing calcium channels to open and release calcium into the cytoplasm.

5th step of skeletal muscle contraction

Calcium ions activate the actin-myosin binding sites and cross-bridges for between the actin and the myosin heads.

6th step of skeletal muscle contraction

An ATP is hydrolyzed to provide energy for flexing the myosin heads.

7th step of skeletal muscle contraction

Flexion brings the actin filaments closer to the middle of the sarcomere. The overall length of the sarcomere is shorter; contracted.

8th step of skeletal muscle contraction

In order for relaxation to occur, ATP must be used to pump calcium back into the sarcoplasmic reticulum.


one of the segments into which a myofibril is divided: smallest function unit in muscle tissue


contractile proteins which interact to cause contraction


thin filaments


thick filaments


makes a "z";
not a line, really a wall;
the border between sarcomeres

Antagonistic action of skeletal muscles?

Muscles can only contract: pull. They can't push. The movement produced by one can be reversed by another. The biceps flexes while the triceps extend.


The muscle that contracts to produce a particular action


The muscle that produces the opposite movement is the antagonist

neuromuscular junction

the junction between a nerve fiber and the muscle it supplies

sarcoplasmic reticulum

The system of vesicles in a muscle cell that surrounds the myofibrils and releases calcium in muscle contraction: modified endoplasmic reticulum

Sliding Filament Theory

When muscle contraction occurs. The actin and myosin filaments temporary form cross-bridge attachments and slide over each other, shortening the overall length of the sarcomeres.


transverse tubules : system of inward extensions of the muscle fiber plasma membrane.

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