Physiology - Membrane Excitation, Excitation-Contraction Coupling

When an action potential is generated in the muscle fiber membrane, it is propagated into what structure?

T-Tubules

When the AP is propagated into the T-Tubules, it brings the AP where?q

The interior of the skeletal muscle fibers

The wave of depolarization during the AP activates the junctional processes of what?

Lateral Sacs

The wave of depolarization activates the junctional processes of the lateral sacs, which releases what?

Ca++

The wave of depolarization activates the junctional processes of the lateral sacs, which releases Ca++ where?

Cytosol

The extensive meshwork of sarcoplasmic reticulum assures that when the lateral sacs release calcium ions they readily diffuse to where?

Troponin sites

Thick filament is mainly composed of what?

Myosin

Myosin is composed of what?

2 heavy chains, 4 smaller light chains

The myosin filaments combine to form a molecule with what characteristics?

2 globular heads (cross bridge) and tail

Heads of myosin contain how many binding sites?

2 (1 for ATP, 1 for actin)

Cross bridges extend from the surface of the thick filaments towards what?

Thin filaments

Thin filaments are mostly made of what?

Actin, troponin, tropomyosin

Actin filament is composed of what?

2 intertwined helical chains

Each chain on the Actin filament contains a binding site for what?

Myosin

What blocks the binding site of 7 actin molecules?

Tropomyosin

What locks tropomyosin in place during rest?

Troponin

How many binding sites does Troponin have?

3

What binds to troponin and "unlocks" tropomyosin?

Ca++

Tropomyosin is "unlocked" how?

Ca++ binds to troponin and causes a conformational change.

Tropomyosin is "locked" how?

Removal of Ca++ from troponin.

If there is low amounts of Ca++ in the cytosol, what does that mean for muscle movement?

Tropomyosin is "locked" and muscles cannot move

After Ca++ is removed from troponin, and tropomyosin returns back to its rest state, what happens to the Ca++?

Shuttled back into the SR (Through Ca++ pump - uses ATP)

What is the 1st step of the Cross-Bridge Cycle?

Attachment of cross bridge to the thin filament

What is the 2nd step of the Cross-Bridge Cycle?

Movement of the cross bridge, producing tension in the thin filament

What is the 3rd step of the Cross-Bridge Cycle?

Detachment of the cross bridge from the thin filament

What is the 4th step of the Cross-Bridge Cycle?

Energizing the cross bridge to repeat the cycle

In the resting state, is the cross bridge energized or unenergized?

Energized (bound ADP and P)

In the resting state, what is the cytoplasmic Ca++ concentration like?

Low

When calcium enters the cell, the energized cross myosin binds to what?

Actin filament

Binding of the actin and myosin triggers the "release" of what?

Cross bridge and ADP and P

Binding of the cross bridge to the actin is broken by ATP binding to what?

Myosin head

What breaks the ATP into ADP and P?

ATP hyrolysis

After use of ATP hydrolysis, what happens to the myosin head

Reenergized

What occurs because there is no ATP being produced, and thus the actin-myosin linked cross bridges cannot be broken?

Rigor Mortis

How long does rigor mortis last?

48 hours

What causes rigor mortis to end?

Decomposition