Mastering A&P Chapter 9 - Muscle Tissue Quiz

Study Notes

Cross Bridge Cycle Initiation

The cross bridge cycle begins when Ca2+ from the sarcoplasmic reticulum binds to troponin.
Elevated Ca2+ levels cause a conformational change in troponin, moving tropomyosin away from actin's myosin-binding sites.

Steps in the Cross Bridge Cycle

Myosin heads bind to actin, forming a cross bridge.
Release of ADP results in the "power stroke," sliding the thin filament towards the sarcomere's center.
ATP binds to myosin, prompting detachment from actin.
ATP is hydrolyzed into ADP and inorganic phosphate (Pi), re-cocking the myosin head.
The cycle continues as long as calcium ions and ATP are present, leading to muscle contraction.

Muscle Fiber Structure

Myosin: Myofilament characterized by a knob-like head, essential for muscle contraction.
Actin: Myofilament that is stabilized by tropomyosin, forming the structure of thin filaments.
Sarcoplasm: The cytoplasm within skeletal muscle fibers, containing necessary organelles and proteins.
Fascicle: Bundles of muscle fibers encased in connective tissue known as perimysium.
Sarcolemma: The plasma membrane surrounding muscle cells, crucial for maintaining ionic gradients.

Sarcomere and Myofilaments

Sarcomere: The fundamental contractile unit of striated muscle, comprising alternating thick (myosin) and thin (actin) filaments.
Myofibrils: Structures made of aligned sarcomeres that run the length of the muscle fiber, facilitating contraction.

Tropomyosin and Muscle Contraction

Tropomyosin blocks the myosin-binding sites on actin when muscle fibers are relaxed, preventing contraction.

Physiological Responses

Cross bridge detachment is significantly hindered when ATP levels drop, leading to muscle stiffness.
In rigor mortis, calcium leaks into the cytoplasm post-mortem, resulting in sustained contraction due to the absence of ATP for detachment.

Important Facts About Cross Bridge Cycling

Detachment requires ATP, thus lacking ATP halts the cycle and maintains cross bridges.
During cycling, only half of myosin heads detach at any time while calcium is available.
Myosin is in an energized state with ADP and Pi bound before the cross bridge cycle initiates.

Description

Test your knowledge on the cross bridge cycle and muscle physiology with this quiz based on Chapter 9 of Mastering Anatomy & Physiology. Understand key concepts including calcium ion dynamics and muscle contraction. Perfect for students seeking to reinforce their understanding of this essential topic.