The electrical event of the heart

Question 1

Which two proteins work together to make a muscle contract?

Answer 1

myosin and actin

Question 2

How is their muscle relaxation?

Answer 2

Tropomyosin blocks actin so that myosin is not able to bind to it.

Question 3

What molecules triggers muscle contraction?

Answer 3

Calcium

Question 4

How does a muscle contract?

Answer 4

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.

Question 5

Initiation of Muscle action potential (EC coupling) in Skeletal Muscle

Answer 5

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

Question 6

What is tetanus?

Answer 6

when there is the buildup of muscle contraction (muscle cramp)

Question 7

What causes tetanus?

Answer 7

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.

Question 8

What are heart cells called?

Answer 8

pacemaker cells

Question 9

What is the function of pacemaker cells

Answer 9

its job is to spontaneously fire

Question 10

Action potential in pacemaker cells

Answer 10

-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

Question 11

Action potential in contractile cells

Answer 11

-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

Question 12

EC coupling in cardiac muscle

Answer 12

1. Action potential comes from neighboring cell or pacemaker cell
2. Goes down T-tubule and opens Ca2+ channels
3. Ca2+ rushes in and opens RyR gate for a second rush of Ca2+ “calcium induced calcium release”
4. summer Ca2+ sparks and creates a Ca2+ signal
5. binds to troponin to initiate contraction
6. Relaxation starts when Ca2+ unbinds to troponin
7. Ca2+ is pumped back into the SR for storage
8. To pump out, Ca2+ is exchanged with Na+ by secondary active transport

Question 13

Which are pacemaker cells?

Answer 13

SA node (the boss)
Internodal pathways
AV node
AV bundle
Bundle branches
Purkinje fibers

Question 14

Specific pathologies to recognize on ECG

Answer 14

1. Arrhythmias (abnormal heart rate)
2. Heart block (traffic between SA and AV)
   - partially: slowed but still go through
   - complete: SA and AV separated (see more p waves than QRS)
3. Atrial vs. ventricular fibrillation (heart muscles dont fire together so dont contract together)
   -atrial effects p waves
   -ventricular more dangerous