repolarization

Examples of repolarization in the following topics:

• Nerve Conduction and Electrocardiograms

  • The depolarization causes the membrane to again become impermeable to Na+, and the movement of K+ quickly returns the cell to its resting potential, referred to as repolarization.
  • Just as nerve impulses are transmitted by depolarization and repolarization of an adjacent membrane, the depolarization that causes muscle contraction can also stimulate adjacent muscle cells to depolarize (fire) and contract.
  • An electrocardiogram (ECG) is a record of the voltages created by the wave of depolarization (and subsequent repolarization) in the heart.
  • The lead II QRS signal also masks the repolarization of the atria.
  • Finally, the T wave is generated by the repolarization of the ventricles and is followed by the P wave in the next heartbeat.

• The Action Potential and Propagation

  • First is depolarization, followed by repolarization and a short period of hyperpolarization.
  • The repolarization or falling phase is caused by the slow closing of sodium channels and the opening of voltage-gated potassium channels.

• Stages of the Action Potential

  • Repolarization.
  • Once the electric gradient has reached the threshold of excitement, the "downswing" of repolarization begins.
  • The sodium gates cannot be opened again until the membrane is repolarized to its normal resting potential.
  • This process of depolarization, repolarization, and recovery moves along a nerve fiber from neuron to neuron like a very fast wave.

• Mechanism and Contraction Events of Cardiac Muscle Fibers

  • CICR creates a "plateau phase" in which the cell's charge stays slightly positive (depolarized) for longer before it becomes more negative as it repolarizes due to potassium ion influx.
  • Skeletal muscle by contrast, repolarizes immediately.

• Mechanics of the Action Potential

  • Repolarization.
  • The "downswing" of repolarization is caused by the closing of sodium ion channels and the opening of potassium ion channels, resulting in the release of positively charged potassium ions (K+) from the nerve cell.
  • The refractory phase is a short period of time after the repolarization stage.
  • The sodium gates cannot be opened again until the membrane has completely repolarized to its normal resting potential, -70 mV.

• Electrocardiogram and Correlation of ECG Waves with Systole

  • The T Wave indicates ventricular repolarization, in which the ventricles relax following depolarization and contraction.
  • The ST segment refers to the gap (normally flat or slightly upcurved line) between the S wave and the T wave, and represents the time between ventricular depolarization and repolarization.
  • Following the T wave is the U wave, which represents repolarization of the Purkinje fibers.

• Nerve Impulse Transmission within a Neuron: Action Potential

  • Signals are transmitted from neuron to neuron via an action potential, when the axon membrane rapidly depolarizes and repolarizes.
  • The action potential is conducted down the axon as the axon membrane depolarizes, then repolarizes.