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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.

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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
slide2

Step 1: ATP hydrolysis

  • Step 2: Attachment
slide3

Step 3: Power Stroke

  • Step 4: Detachment
contraction and movement overview interactions animation
Contraction and Movement OverviewInteractions Animation
  • Contraction and Movement

You must be connected to the internet to run this animation.

length tension relationship
Length-Tension Relationship
  • Sarcomere shortening produces tension within a muscle

Compressed thick filaments

Limited contact between actin and myosin

excitation contraction coupling
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

slide8

Neuromuscular Junction

  • Excitation-Contraction coupling (EC coupling) involves events at the junction between a motor neuron and a skeletal muscle fiber
neuromuscular junction
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”

neuromuscular junction1
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 junction2
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 junction3
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 interactions animation
Neuromuscular JunctionInteractions Animation
  • Neuromuscular Junctions

You must be connected to the internet to run this animation.

muscle action potential
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
muscle action potential1
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)