6.3.2 Mechanism of Muscle Contraction

• Skeletal muscles are controlled involuntarily.

  False
• The cell membrane surrounding the muscle fiber is called the sarcolemma
• Order the steps of the sliding filament theory:

  1️⃣ Motor neuron releases acetylcholine

  2️⃣ Depolarization causes calcium release

  3️⃣ Calcium binds to troponin

  4️⃣ Cross-bridges form between actin and myosin

  5️⃣ Power stroke shortens the sarcomere

  6️⃣ ATP detaches myosin heads

  7️⃣ Myosin heads reactivate
• What molecule provides energy for the power stroke in muscle contraction?

  ATP
• What is the role of the sarcolemma in muscle fibers?

  Cell membrane
• What causes the sarcoplasmic reticulum to release calcium ions?

  Depolarization
• What molecule is hydrolyzed during the power stroke to provide energy?

  ATP
• What neurotransmitter is released by motor neurons to activate muscle contraction?

  Acetylcholine
• Actin forms the thick filaments in the sarcomere.

  False
• During contraction, myosin heads pull actin filaments closer to the M-line
• What molecule causes myosin heads to detach from actin during cross-bridge detachment?

  ATP
• Match the muscle type with its control and function:

  Skeletal ↔️ Voluntary, Movement

  Smooth ↔️ Involuntary, Peristalsis

  Cardiac ↔️ Involuntary, Heartbeat
• Match the muscle type with its location, control, and function:

  Skeletal ↔️ Attached to bones, voluntary, movement

  Smooth ↔️ Walls of organs, involuntary, peristalsis

  Cardiac ↔️ Heart, involuntary, pumping blood
• What is the function of cardiac muscle?

  Pumping blood
• Within each sarcomere, actin and myosin filaments are arranged in an overlapping pattern
• Cross-bridge detachment requires ATP.


  True
• What are the basic contractile units within myofibrils called?

  Sarcomeres
• The sliding filament theory explains how sarcomeres shorten during muscle contraction.


  True
• Myosin heads bind to actin filaments, forming cross-bridges
• The sliding filament theory explains how skeletal muscles contract
• Steps of the sliding filament theory

  1️⃣ Motor neuron releases acetylcholine

  2️⃣ Calcium ions are released from the sarcoplasmic reticulum

  3️⃣ Calcium binds to troponin, exposing myosin-binding sites

  4️⃣ Cross-bridges form between actin and myosin

  5️⃣ Power stroke shortens the sarcomere

  6️⃣ Cross-bridges detach with ATP binding

  7️⃣ Myosin heads reactivate for the next stroke
• What is the function of myosin in muscle contraction?

  Pulls actin filaments
• ATP is required for the power stroke during muscle contraction.

  True
• What are the three main types of muscle tissue in the body?

  Skeletal, Smooth, Cardiac
• Match the muscle type with its location, control, and function:

  Skeletal ↔️ Attached to bones, voluntary, movement

  Smooth ↔️ Walls of organs, involuntary, peristalsis

  Cardiac ↔️ Heart, involuntary, pumping blood
• Where are cardiac muscles located?

  Heart
• The sarcoplasm is the cytoplasm within a muscle fiber.

  True
• Actin and myosin filaments slide past each other during muscle contraction.


  True
• Calcium ions are released from the sarcoplasmic reticulum
• What are the two main proteins responsible for muscle contraction?

  Actin and myosin
• Steps in cross-bridge formation and movement during muscle contraction:

  1️⃣ Myosin heads bind to actin filaments

  2️⃣ Power stroke: Myosin heads pull actin closer

  3️⃣ Cross-bridge detachment: ATP binds to myosin

  4️⃣ Myosin reactivation: ATP is hydrolyzed
• What happens during the power stroke in muscle contraction?

  Myosin heads pivot and pull
• What exposes the myosin-binding sites on actin filaments during cross-bridge formation?

  Calcium ions
• Steps in the sliding filament theory during muscle contraction

  1️⃣ Cross-Bridge Formation

  2️⃣ Power Stroke

  3️⃣ Cross-Bridge Detachment

  4️⃣ Myosin Reactivation
• The hydrolysis of ATP releases energy as it is converted into ADP and inorganic phosphate
• Steps in excitation-contraction coupling

  1️⃣ Muscle Activation: Motor neuron releases acetylcholine

  2️⃣ Action Potential Propagation: Depolarization spreads across the sarcolemma

  3️⃣ Calcium Release: Sarcoplasmic reticulum releases calcium ions

  4️⃣ Myosin Binding: Calcium exposes myosin-binding sites on actin

  5️⃣ Muscle Contraction: Myosin heads bind and pull actin
• What molecule does calcium bind to in order to expose the myosin-binding sites on actin filaments?

  Troponin
• Match the step in excitation-contraction coupling with its key molecule

  Motor neuron releases acetylcholine ↔️ Acetylcholine

  Depolarization spreads ↔️ Action Potential

  Calcium release from sarcoplasmic reticulum ↔️ Calcium ions

  Cross-bridge formation ↔️ Actin, Myosin
• Match the muscle type with its control and function

  Skeletal ↔️ Voluntary, Movement

  Smooth ↔️ Involuntary, Peristalsis

  Cardiac ↔️ Involuntary, Pumping blood
• During muscle contraction, actin and myosin filaments slide past each other, shortening the sarcomere


  True