Muscular 3

• What are sarcomeres?


  Sarcomeres are the basic functional units of muscle fibers.
• What are the key components of a sarcomere?

  - Z lines: The ends of the sarcomeres - M lines: The midpoints of the sarcomeres - Thin actin filaments: Branch from Z lines towards the middle - Thick myosin filaments: Branch from M lines towards the ends - I band: Area where only actin filaments are present - A band: Area where actin and myosin overlap - H zone: Area where only myosin is present
• What is the function of Z lines in a sarcomere?

  Z lines serve as anchor points for thin filaments and define sarcomere boundaries.
• What role do M lines play in a sarcomere?

  M lines stabilize thick filaments and maintain sarcomere structure.
• What is the function of thin actin filaments in a sarcomere?

  Thin actin filaments provide binding sites for myosin heads during contraction.
• How do thick myosin filaments contribute to muscle contraction?

  Thick myosin filaments generate force for muscle contraction via cross-bridge cycling.
• What is the I band in a sarcomere?


  The I band is the area where only actin filaments are present.
• What does the A band represent in a sarcomere?

  The A band is the area where actin and myosin overlap.
• What is the H zone in a sarcomere?

  The H zone is the area where only myosin is present.
• What are the changes in sarcomere components during muscle contraction?

  - H zone shortens as myosin heads pull actin filaments towards the center - I band shortens as actin filaments are pulled inward - A band maintains a constant length
• What is a twitch contraction?

  A twitch contraction is the contraction of a muscle fiber through motor unit stimulation.
• What are the characteristics of twitch contractions?

  Each twitch has the same size and duration and follows the all-or-none principle.
• What does the all-or-none principle state regarding twitch contractions?

  The all-or-none principle states that a depolarization above threshold potential causes all muscle fibers to twitch, while below threshold potential causes no twitching.
• What happens if a muscle fiber receives a stimulus below the threshold potential?

  No contraction will occur.
• What occurs when a muscle fiber receives a stimulus exactly at the threshold potential?

  A full contraction of the muscle fiber occurs.
• When will a muscle fiber contract if it receives multiple stimuli of increasing strength?

  The muscle fiber will contract when the stimulus reaches the threshold potential.
• What happens when a muscle fiber receives a stimulus exactly at the threshold potential?

  The muscle fiber contracts fully.
• How does the all-or-none principle ensure consistent muscle contractions?

  The all-or-none principle ensures that a muscle fiber will either contract fully or not at all, depending on whether the stimulus reaches the threshold potential.
• What does the all-or-none principle state regarding muscle fiber contraction?

  A muscle fiber will contract fully when the stimulus reaches or exceeds the threshold potential.
• What happens when a stimulus is below the threshold potential?

  No contraction occurs.
• How does the strength of a stimulus affect muscle fiber contraction according to the all-or-none principle?

  The strength of the stimulus does not affect the contraction; it either contracts fully or not at all.
• What is the significance of the all-or-none principle in muscle physiology?


  It ensures that muscle responses are consistent and predictable.
• What are the three phases of a twitch contraction?

  1. **Latent phase**: - Action potential spreads over sarcolemma and T-tubules - Signals sarcoplasmic reticulum to release calcium 2. Contraction phase: - Cross bridges form as calcium ions bind to troponin - H zones shrink - Muscle tension increases 3. Relaxation phase: - Calcium is pumped back into the sarcoplasmic reticulum - Cross bridge cycling ends - Muscle tension decreases
• During which phase of a twitch contraction does the action potential spread and calcium is released?

  Latent phase
• What occurs during the contraction phase of a twitch contraction?

  Cross bridges form as calcium ions bind to troponin, leading to increased muscle tension.
• What happens during the relaxation phase of a twitch contraction?

  Calcium is pumped back into the sarcoplasmic reticulum, and muscle tension decreases.
• What is a motor unit and its components?

  - A motor unit consists of: - A single motor neuron - All the muscle fibers it innervates
• What are the types of motor units and their characteristics?

  1. **Small motor units**: - Few muscle fibers - Used in precision movements (e.g., eye muscles) 2. Large motor units: - Many muscle fibers - Used in powerful movements (e.g., leg muscles)
• How do motor units contribute to muscle contractions?

  Motor units allow for graded muscle contractions by recruiting different numbers of units based on the required force.
• Which type of motor unit is primarily used for fine hand movements, such as writing?

  Small motor units
• What is the difference in function between small and large motor units?

  Small motor units are used for precision movements, while large motor units are used for powerful movements.