Question

Phenytoin (sodium channel blocker) and ethosuximide (calcium channel blocker) are anti-seizure drugs that stop seizures from happening. These drugs work by inhibiting electrical impulses (action potentials) from occurring. Explain the importance of sodium and calcium channels on a neuron and and the reasons why action potentials do not occur when these channels are inhibited. Be sure to include the phases of an action potential, the channels involved, and the importance of an action potential.

Answer 1

Answer-

Action potential-It is the potential or power or electrical energy required to generate impulses and provides communication between the neurons is called action potential. Normally cell membrane consists of potential is called resting membrane potential() -70mV. The action potential is due to exchange of different ions across the membrane.

Phases of the action potential -

Depolarizing Phase-When a depolarizing graded potential causes the axon membrane to depolarize to threshold, voltage-gated Na+ channels open rapidly. The influx of sodium ions causes the depolarizing phase of the action potential. Sodium ions move along their electrical and chemical concentration gradient. The inflow of Na+ changes the membrane potential from - 55 mV to + 30 mV.

The voltage-gated sodium ion channel has two gates. The inactivation gate opens at -70 mV and closes at +30 mV. The activation gate opens at -55 mV and closes at -70mV.

Repolarizing Phase-When the voltage-gated Na+ channel is in an inactivated state, the activation gates of the channel are open and the inactivation gates are closed. In addition to opening voltage-gated Na+ channels, a depolarizing graded potential also opesn voltage-gated K+ channels. The slower opening of voltage-gated K+ channels and the closing of previously opened voltage-gated Na+ channels produce the repolarizing phase of the action potential. Slowing of Na+ inflow and acceleration of K+ outflow causes the membrane potential to change from + 30 mV to -70 mV.

Hyperpolarizing phase-in this stage the potassium channels remain open and causes repolarization and comes to normal membrane potential.

The generation of impulses(depolarization) in neuron mainly depends on influx sodium and calcium ions without these ions, no action potential developed and neuron firing does not occur.

If the drugs inhibit these channels, no depolarization, no action potential, no neuronal firing or communication.

The channels involved in an action potential are voltage-gated sodium channels, potassium channels, and calcium channels.

The action potential is required for transmission of information one are to another area in the body.

The responses to different stimuli is due to action potential.