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Anatomy and Physiology

Anatomy and Physiology. Chapter 8. There are three different types of muscles: Smooth muscle tissue has no striations (lines) and is not generally under conscious control. Generates force but acts very slowly. Skeletal muscle tissue has striations and is under conscious control.

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Anatomy and Physiology

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  1. Anatomy and Physiology Chapter 8

  2. There are three different types of muscles: • Smooth muscle tissue has no striations (lines) and is not generally under conscious control. • Generates force but acts very slowly. • Skeletal muscle tissue has striations and is under conscious control. • Generates significant force and can respond very quickly. • Cardiac muscle tissue is similar to skeletal muscles, but contains intercallated discs, which help synchronize the heartbeat.

  3. Muscles are made up of a hierarchy of smaller and smaller units. • Skeletal muscles are made of fibers that run the length of the muscle. • Each fiber is a single cell with many nuclei. • The fibers consist of smaller myofibrils

  4. Each myofibril is made up of thin filaments (actin + tropomyosin + troponin) and thick filaments (myosin) • The myofibril is divided into groups of thin and thick filaments called a sarcomere. • Each sarcomere is separated by Z-lines.

  5. This sarcomere consists of several sections • Z-line - the borders of the sarcomere • I-band - area near Z-lines where there are only thin filaments. • A-band - region that corresponds to the length of the thick filaments. Part is dark, part is light. • H-zone - only thick filaments

  6. Muscle Contraction • Contraction takes place according to the sliding filament model. • Neither the thick filaments nor the thin filaments change length. • They slide past each other • Sarcomere shortens (Z-lines come closer together).

  7. This contraction will occur when a myosin breaks down an ATP molecule to change its shape to its high energy conformation. • The myosin holds on to the ADP + P • The myosin head will bind to an actin filament.

  8. The myosin then releases the ADP + P and relaxes into its low energy state. • Since it is still attached to the actin, this results in a force on the actin. • Another ATP molecule binds to the myosin changing it to its low energy conformation. • Repeat

  9. This process is regulated by Calcium ion (Ca+2) levels in the muscle cell cytoplasm. • A signal is sent to the muscle cell by a neuron through the use of Acetylcholine. • This signal causes the Sarcoplasmic reticulum to release Ca+2 ions.

  10. The Ca+2 ions bind to troponin molecule that is part of the thin filament. • This binding causes the troponin to change shape which causes the tropomyosin to move. • When the tropomyosin moves, myosin binding sites on the actin are uncovered. • This allows the myosin to bind to the actin. • When the Ca+2 ions are in low concentration, the troponin molecule changes shape again and moves the tropomyosin back to its original position.

  11. Major Muscles • Muscles tend to come in pairs called flexors and extensors • Flexors decrease the angle between two bones • Extensors increase the angle between two bones • Ex: Biceps brachii flexes the elbow while the triceps brachii extends it.

  12. The End

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