lecture 11 pt9

Depolarization Phase

• Depolarization is the initial phase where sodium channels open.

• As depolarization finishes, potassium channels begin to open, signaling the start of repolarization.

Repolarization

• During repolarization, the membrane potential begins to fall, moving back towards a negative charge.

• Voltage-gated potassium channels play a critical role, allowing potassium ions to leave the cell, counteracting the positive charge build-up from sodium influx.

Hyperpolarization

• After repolarization, the cell briefly becomes hyperpolarized, reaching a more negative state than the resting potential before returning to baseline.

Refractory Period

• Two types: absolute refractory period (no action potential generated) and relative refractory period (possible to stimulate, but challenging).

• This refractory period ensures that the action potential does not reverse direction, maintaining the impulse's forward momentum.

Action Potential Propagation

• The action potential travels along the axon, initiating neighboring sodium channels to open via depolarization.

• Potassium efflux aids in repolarization, restoring the resting potential quickly (in 1-2 milliseconds).

Role of Myelin

• Myelin sheath facilitates saltatory conduction, allowing faster impulse transmission by enabling action potentials to jump between nodes of Ranvier.

Action Potential vs. Impulse

• The terms "action potential" and "impulse" can be used interchangeably to describe the electrical signal traveling along the neuron.

• Understanding these concepts is critical for exam preparation as they are fundamental to neurophysiology.

Exam Preparation Tips

• Focus on the mechanisms of depolarization, repolarization, and the refractory periods.

• Review the role of ion channels in the action potential process.

• Consider visual aids, such as diagrams of the axon and action potential phases, to enhance understanding.