Download Chapter 9 Joints - Dr. Jerry Cronin

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
Contraction and Movement Overview
Interactions Animation
• Contraction and Movement
You must be connected to the internet to run this animation.
Length-Tension Relationship
• Sarcomere shortening produces tension within a
muscle
Compressed
thick
filaments
Limited
contact
between actin
and myosin
Excitation-Contraction Coupling
• We will come back to the term excitationcontraction 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
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 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 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
Interactions Animation
• Neuromuscular Junctions
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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 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)