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The Sliding-Filament Mechanism

The Sliding-Filament Mechanism. The “sliding” of actin on myosin (thick filaments on thin filaments) can be broken down into a 4 step process. Step 1: ATP hydrolysis Step 2: Attachment. Step 3: Power Stroke Step 4: Detachment. The Sliding-Filament Mechanism.

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The Sliding-Filament Mechanism

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  1. The Sliding-Filament Mechanism • The “sliding” of actin on myosin (thick filaments on thin filaments) can be broken down into a 4 step process

  2. Step 1: ATP hydrolysis • Step 2: Attachment

  3. Step 3: Power Stroke • Step 4: Detachment

  4. The Sliding-Filament Mechanism

  5. Contraction and Movement OverviewInteractions Animation • Contraction and Movement You must be connected to the internet to run this animation.

  6. Length-Tension Relationship • Sarcomere shortening produces tension within a muscle Compressed thick filaments Limited contact between actin and myosin

  7. Excitation-Contraction Coupling • We will come back to the term excitation-contraction coupling in a little bit • Before we can describe the entire process, from thinking of moving a muscle to actual contraction of sarcomeres, we must first explore the processes that occur at the neuromuscular junction

  8. Neuromuscular Junction • Excitation-Contraction coupling (EC coupling) involves events at the junction between a motor neuron and a skeletal muscle fiber

  9. Neuromuscular Junction • An enlarged view of the neuromuscular junction • The presynaptic membrane is on the neuron while the postsynaptic membrane is the motor end plate on the muscle cell. The two membranes are separated by a space, or “cleft”

  10. Neuromuscular Junction • Conscious thought (to move a muscle) results in activation of a motor neuron, and release of the neurotransmitter acetylcholine (AcCh) at the NM junction • The enzyme acetylcholinesterase breaks down AcCh after a short period of time

  11. Neuromuscular Junction • The plasma membrane on the “far side” of the NMJ belongs to the muscle cell and is called the motor end plate • The motor end plate is rich in chemical (ligand) - gated sodium channels that respond to AcCh. Another way to say this: The receptors for AcCh are on the ligand-gated sodium channels on the motor end plate

  12. Neuromuscular Junction • The chemical events at the NMJ transmit the electrical events of a neuronal action potential into the electrical events of a muscle action potential

  13. Neuromuscular JunctionInteractions Animation • Neuromuscular Junctions You must be connected to the internet to run this animation.

  14. Muscle Action Potential • The muscle AP is propagated over the surface of the muscle cell membrane (sarcolemma) via voltage (electrical)-gated Na+ and K+ channels

  15. Muscle Action Potential • By placing a micropipette inside a muscle cell, and then measuring the electrical potential across the cell membrane, the phases of an action potential (AP) can be graphed (as in this figure)

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