• Scaffolding proteins help muscles keep their shape
• Binding sights for proteins involved in signaling cascades
Titin: attached to myosin
Nebulin: attached to actin
Give the muscle strength, allow it to shorten
Muscular Dystrophy is a dissolving of the proteins involved in distrophin (which connects actin
to the sarcolemma) and the muscle is unable to shorten. Over time the membranes disintegrate
and it leads to loss of function.
Z line: at the end of the sarcomere
M line: down the middle
Initiation of Muscle Contraction
1. Alpha-motor neuron is stimulated and propagates the action potential along the nerve
Depolarization (where there is a movement of charge across cell membrane) moves
2. Action potential crosses neuromuscular junction
You can have one nerve stimulating multiple muscle fibres
3. Action potential enters muscle and causes calcium release
Calcium is released, cross bridges interact
Action potential: rapid and sustained depolarization of the nerve membrane
• Membrane must first reach threshold before action potential can occur.
Resting Membrane Potential
There has to be a change in polarity that reaches a certain threshold.
-70mv inside cell originates because of permeability to potassium of the membrane
Membrane permeable to K+: any potassium outside the cell will leak inwards
As the quantity inside the cell increases so does the voltage
Membrane proteins are negative. Stays inside cell.
Chloride is repelled outside of the cell because of the negative charge
Result is a small negative charge
Depolarization: Positive spike of charge in cell membrane
Repolarization: environment being manipulated to its original state
1. Na+ Voltage gated channels open and leads to an influx of sodium inside cell
o For a brief moment the cell will be + charged The change in voltage along nerve propagates AP to next area because of voltage gated
channels react to the change in polarity.
It is the continual movement of sodium outside of the cell entering the cell that leads to action
2. K+ channels open and potassium rushes outside cell
o restores the resting membrane potential.
o Originally it was because of the sodium outside and potassium inside.
o Fixed polarity but the elements are changed.
The events up to now have just been reactions to change in polarity.
3. Na+/K+ pump that restores sodium outside and potassium inside
o This is an energy requiring process
o Sodium potassium ATPase
Some ATP that is being regenerated through aerobic metabolism is going to be utilized within
• The SA node is surrounded by an artery that gives it its own blood flow. Always has
oxygen available to do this aerobically
Nerve Conduction Velocity
Different types of axons:
Non-myelinated: does not have insulation/covering
• Some of the impulse is leaked into surrounding tissue
Myelinated: series of myelinated areas. These propagate the AP faster
• Myelin is composed of about 80% lipids and about 20% protein.
• In myelinated axons, action potentials do not propagate as waves but recur at
successive nodes – Nodes of Ranvier - and in effect “hop” along the axon
• Skeletal muscle that has to generate force fast (fast twitch fibres) are myelinated
The gaps between myelin sheath cells are nodes of Ranvier. The electrical impulse jumps from
one node to the next in 120 m/s. This is called saltatory conduct