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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. - PowerPoint PPT Presentation
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• The “sliding” of actin on myosin (thick filaments on thin filaments) can be broken down into a 4 step process
The Sliding-Filament Mechanism
• Step 1: ATP hydrolysis
• Step 2: Attachment
• Step 3: Power Stroke
• Step 4: Detachment
The Sliding-Filament Mechanism
Contraction and Movement OverviewInteractions Animation
• Contraction and Movement
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Limited contact between actin and myosin
Compressed thick
filaments
Length-Tension Relationship• Sarcomere shortening produces tension within a muscle
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
• Excitation-Contraction coupling (EC coupling) involves events at the junction between a motor neuron and a skeletal muscle fiber
Neuromuscular Junction
• An enlarged view of the neuromuscular junctionThe 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”
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
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
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
Neuromuscular Junction
Neuromuscular JunctionInteractions Animation
• Neuromuscular Junctions
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• The muscle AP is propagated over the surface of the muscle cell membrane (sarcolemma) via voltage (electrical)-gated Na+ and K+ channels
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)
Muscle Action Potential