The electrical event of the heart Flashcards
Which two proteins work together to make a muscle contract?
myosin and actin
How is their muscle relaxation?
Tropomyosin blocks actin so that myosin is not able to bind to it.
What molecules triggers muscle contraction?
Calcium
How does a muscle contract?
Calcium is released and binds to Troponin which causes it to change shape. Tropomyosin moves away, not blocking actin, which allows for myosin head to bind to actin and completes power stroke.
Initiation of Muscle action potential (EC coupling) in Skeletal Muscle
Signal comes from motor neuron -> Acetylcholine is released and binds to motor end plate receptors -> triggers the release of Na+ -> action potential goes through T-tubule -> reaches DHP which causes a structure change and pulls RyR to open the gate -> Ca2+ starts to flow out -> calcium then binds to Troponin -> Tropomyosin shys away, causing power stroke -> ATP used to pump Ca2+ back to sarcoplasmic reticulum
What is tetanus?
when there is the buildup of muscle contraction (muscle cramp)
What causes tetanus?
action potentials are fired faster than the process of muscle contraction, so as muscle contraction is still ongoing, more and more action potentials are being fired. This leads to the buildup of continuous muscle contractions and causes tetanus.
What are heart cells called?
pacemaker cells
What is the function of pacemaker cells
its job is to spontaneously fire
Action potential in pacemaker cells
-no stabilized membrane potential
-after hyperpolarization, just gradually increases
-funny channels: specialized hyperpolarized opening ion channel (not selective, Na+ flow in and K+ flow out, but more Na+ flows in so still net positive)
funny channel opens which gradually depolarizes the cells, reaches the threshold and opens voltage gated Ca2+ channels, Ca2+ flows in, Ca2+ channel closes while K+ channels open, K+ channels close and funny channel opens again
Action potential in contractile cells
-stable resting membrane potential (-90)
1. voltage gated Na+ channel opens
2. When reach 20 mV, Na+ channels closes and K+ and Ca2+ channels open ( K+ flows out and Ca2+ flows in)
this is to make the potential last longer in order to match the timing of contraction for no tetanus
3. Ca2+ channels close and late K+ channels open
EC coupling in cardiac muscle
- Action potential comes from neighboring cell or pacemaker cell
- Goes down T-tubule and opens Ca2+ channels
- Ca2+ rushes in and opens RyR gate for a second rush of Ca2+ “calcium induced calcium release”
- summer Ca2+ sparks and creates a Ca2+ signal
- binds to troponin to initiate contraction
- Relaxation starts when Ca2+ unbinds to troponin
- Ca2+ is pumped back into the SR for storage
- To pump out, Ca2+ is exchanged with Na+ by secondary active transport
Which are pacemaker cells?
SA node (the boss)
Internodal pathways
AV node
AV bundle
Bundle branches
Purkinje fibers
Specific pathologies to recognize on ECG
- Arrhythmias (abnormal heart rate)
- Heart block (traffic between SA and AV)
- partially: slowed but still go through
- complete: SA and AV separated (see more p waves than QRS) - Atrial vs. ventricular fibrillation (heart muscles dont fire together so dont contract together)
-atrial effects p waves
-ventricular more dangerous