Muscle Contraction Cycle Flashcards

Muscle Contraction Cycle Overview

• Muscle contraction initiates once the muscle cell is excited and ready to contract.
• A muscle action potential triggers the release of calcium ions (Ca2+) into the sarcoplasm, essential for contraction.

Role of Calcium Ions

• Calcium ions bind to regulatory proteins in muscle fibers, initiating the contraction process.
• Calcium release occurs in the sarcoplasm as a response to a single nervous signal, acting as a trigger for the contraction cycle.

Contraction Cycle Steps

• The contraction cycle consists of four key steps:
  • ATP Hydrolysis
  • Cross Bridge Attachment
  • Power Stroke
  • Cross Bridge Detachment

Step 1: ATP Hydrolysis

• ATP (adenosine triphosphate) energizes myosin molecules, enabling them to perform power strokes necessary for contraction.

Step 2: Cross Bridge Attachment

• Myosin heads temporarily attach to actin filaments, forming cross bridges essential for muscle contraction.

Step 3: Power Stroke

• Myosin filaments pull the actin filaments during the power stroke after phosphate is released, sliding the filaments and causing contraction. ADP is also released during this phase.

Step 4: Cross Bridge Detachment

• The binding of a new ATP molecule to the myosin cross bridge results in detachment from actin, allowing the cycle to repeat.

Contraction Cycle Continuity

• The contraction cycle continues as long as myosin ATPase can hydrolyze newly attached ATP molecules.

Conditions for Continued Contraction

• Sustained contraction is dependent on the availability of ATP and high calcium ion levels near thin filaments.

Maximum Contraction

• During maximum muscle contraction, the distance between Z discs can reduce to half their resting length, indicating a fully contracted state.