9.3 Muscle Contraction

• Contracting muscle fibers exert a pull or tension and shortens in length
• The Sliding Filament Theory
• The Sliding Filament Theory... contracting muscle fibers with changes:

  • H bands and I bands get smaller
  • Zone of overlap gets larger
  • Z lines move closer together
  • A band remins constant
• Sliding Filament Theory explains changes in filament interaction during contraction
• Sliding Filament Theory steps:

  • Contraction cycle begins
  • Active-site exposure
  • Cross-bridge formation
  • Myosin head pivoting
  • Cross-bridge detachment
  • Myosin reactivation
• Skeletal muscle contraction has a sequence of events
• • Motor neuron chemicals change the sarcolemma's membrane potential, spreading to T tubules
  • T tubule potentials change triggers sarcoplasmic reticulum to release calcium, starting contraction
• Skeletal muscle fibers are controlled by motor neurons from central nervous system
• Axon terminal is the expanded tip of the axon at neuromuscular junction
• Cytoplasm of the axon terminal contains mitochondria and small secretory vesicles, this is called the synaptic vesicles
• Vesicles contain molecules of neurotransmitter acetylcholine ACh
• The synaptic cleft is a narrow space separating the axon terminal from the motor end plate of the skeletal muscle fiber
• Acetylcholinesterase AChe is an enzyme in the synaptic cleft used to break down molecules of ACh
• Muscle Contraction: Summary. First.

  • At the neuromuscular junction, ACh is released by the axon terminal which binds to receptors on the sarcolemma
• Muscle Contraction: Summary. First.

  • At the neuromuscular junction, ACh is released by the axon terminal which binds to receptors on the sarcolemma
• Muscle Contraction: Summary. Second.

  • Resulting change in membranous potential of muscle fiber leads to production of action potential, spreads across the surface and T tubules
• Muscle Contraction: Summary. Second.

  • Resulting change in membranous potential of muscle fiber leads to production of action potential, spreads across the surface and T tubules
• Muscle Contraction: Summary. Third.

  • Sarcoplasmic reticulum releases stored calcium ions, increasing calcium concentration in the sarcoplasm and around sarcomeres
• Muscle Contraction: Summary. Third.

  • Sarcoplasmic reticulum releases stored calcium ions, increasing calcium concentration in the sarcoplasm and around sarcomeres
• Muscle Contraction: Summary. Four.

  • Calcium ions bind to troponin, makes change, exposing active sites on thin (actin) filaments. Myosin cross-bridges form
• Muscle Contraction: Summary. Four.

  • Calcium ions bind to troponin, makes change, exposing active sites on thin (actin) filaments. Myosin cross-bridges form
• Muscle Contraction: Summary. Five.

  • Myosin and actin continue grabbing, pulling, and letting go of each other using ATP. Actions cause filament sliding and muscle fiber shortens
• Muscle Contraction: Summary. Five.

  • Myosin and actin continue grabbing, pulling, and letting go of each other using ATP. Actions cause filament sliding and muscle fiber shortens
• Muscle Contraction: Summary. Six.

  • Action potential generation stops as ACh diffuses out of the synapse or broken down by AChE
• Muscle Contraction: Summary. Six.

  • Action potential generation stops as ACh diffuses out of the synapse or broken down by AChE
• Muscle Contraction: Summary. Seven.

  • Sarcoplasmic reticulum reabsorbs calcium ions, so the concentration of calcium ions in the sarcoplasm decreases
• Muscle Contraction: Summary. Seven.

  • Sarcoplasmic reticulum reabsorbs calcium ions, so the concentration of calcium ions in the sarcoplasm decreases
• Muscle Contraction: Summary. Eight.

  • A calcium ion concentration of the normal amount while the troponin tropomyosin complex returns to position
• Muscle Contraction: Summary. Eight.

  • A calcium ion concentration of the normal amount while the troponin tropomyosin complex returns to position
• Muscle Contraction: Summary. Nine.

  • Without cross-bridge interactions, no sliding, contraction ends
• Muscle Contraction: Summary. Nine.

  • Without cross-bridge interactions, no sliding, contraction ends
• Muscle Contraction: Summary. Ten.

  • Muscle relaxation and muscle fiber returns to resting length
• Muscle Contraction: Summary. Ten.

  • Muscle relaxation and muscle fiber returns to resting length
• Steps that initiate a muscle contraction. One.

  • ACh released, binding to receptors
• Steps that initiate a muscle contraction. One.

  • ACh released, binding to receptors
• Steps that initiate a muscle contraction. Two.

  • Action potential reaches T tubule
• Steps that initiate a muscle contraction. Two.

  • Action potential reaches T tubule
• Steps that initiate a muscle contraction. Three.

  • Sarcoplasmic reticulum releases calcium
• Steps that initiate a muscle contraction. Three.

  • Sarcoplasmic reticulum releases calcium
• Steps that initiate a muscle contraction. Four.

  • Active site exposure and cross-bridge formation