Mastering A&P Chapter 9 - Muscle Tissue Quiz

Questions and Answers

The cross bridge cycle starts when ________.

Ca2+ from the sarcoplasmic reticulum binds to troponin

Place the steps that occur during a single cross bridge cycle in the correct order from left to right.

Activated myosin head binds to actin, forming a cross bridge. (correct)

ATP is hydrolyzed to ADP and Pi and the energy released re-cocks the myosin head. (correct)

ATP binds to the myosin head and detaches it from actin. (correct)

ADP is released and myosin slides the thin filament toward the center of the sarcomere. (correct)

What is myosin?

Myofilament with a knob-like head

What is actin?

Myofilament stiffened and stabilized by tropomyosin Signup and view all the answers

What is sarcoplasm?

The cytoplasm of a skeletal muscle fiber Signup and view all the answers

What is a fascicle?

Bundle of skeletal muscle fibers enclosed by connective tissue called perimysium Signup and view all the answers

What is the sarcolemma?

Membrane of muscle cell Signup and view all the answers

What blocks myosin-binding sites on actin?

Tropomyosin Signup and view all the answers

What are skeletal muscle fibers?

Long, cylindrical cells Signup and view all the answers

What is a sarcomere?

Contractile unit Signup and view all the answers

What are myofibrils?

Made up of several sarcomeres Signup and view all the answers

In the event that a muscle cell runs out of ATP, what step of the cross bridge cycle is most directly inhibited or terminated?

Cross bridge detachment Signup and view all the answers

What best explains rigor mortis after death?

Cross bridge detachment cannot occur. Signup and view all the answers

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.