KP222 Lecture 12: KP222 - L12
Lecture 12:
Signal for depolarization: from another cardiac cell
- Coming from the pacemaker cell to the gap junctions
- Right from the SA node
1. Sodium influx
- Na channels inactivate and causes an initial period of repolarization
2. Plateau region
- Closing of potassium channels (inward rectifier channels KIR)
- KIR open at rest = slow repolarization
- Opening of L type channels
- Want them to be slower, need the influx because that wil generate the force for
crossbridge cycling
3. Delayed rectifiers
- Open up and allows K to reach equilibrium and speeds up the repolarization
- Repolarizing: L type can not stay open and they close
Why doesn’t the ECG look like an AP?
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Reflex conduction of electricity in a structure that’s highly complex
Ventricular depolarization: starts with action potentials
Atrial depolarization
Excitation- Contraction Coupling in the heart
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Need depolarization
- Current of positive charge through the ICF environment
- Travel along the Sacrolemma
- Activate and open voltage gated calcium channels
- L-type calcium channels
- The plateau phase: opening of calcium channels and closing of potassium channels
- Binding to troponin and exposing myosin binging sites
- Calcium flowing in induces calcium (step 4)
- The presence of the calcium has an effect on the sarcoplasmic reticulum
Wave of depolarization down T tubules
- Activation of the ryanodine receptors
- Need relaxation
- ATPase pumps
- SERCA pumps
- Also have sodium exchanger: bring Ca in and out
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Document Summary
Coming from the pacemaker cell to the gap junctions. Right from the sa node: sodium influx. Na channels inactivate and causes an initial period of repolarization: plateau region. Want them to be slower, need the influx because that wil generate the force for. Closing of potassium channels (inward rectifier channels kir) Kir open at rest = slow repolarization crossbridge cycling: delayed rectifiers. Open up and allows k to reach equilibrium and speeds up the repolarization. Repolarizing: l type can not stay open and they close. Reflex conduction of electricity in a structure that"s highly complex. Current of positive charge through the icf environment. The plateau phase: opening of calcium channels and closing of potassium channels. Binding to troponin and exposing myosin binging sites. The presence of the calcium has an effect on the sarcoplasmic reticulum. Also have sodium exchanger: bring ca in and out. Atrial pressure: two times the diastolic pressure + systolic pressure / 3.
