Question Video: Identifying the Votage-Gated Ions Channels Involved in a Nerve Impulse | Nagwa Question Video: Identifying the Votage-Gated Ions Channels Involved in a Nerve Impulse | Nagwa

Question Video: Identifying the Votage-Gated Ions Channels Involved in a Nerve Impulse Biology • Second Year of Secondary School

Join Nagwa Classes

Attend live Biology sessions on Nagwa Classes to learn more about this topic from an expert teacher!

The flowchart provided outlines the stages of an action potential. What element should replace the gaps in the first four statements?

03:09

Video Transcript

The flowchart provided outlines the stages of an action potential. What element should replace the gaps in the first four statements? Stage one, the axon membrane has a resting potential of minus 65 millivolts; blank voltage-gated ion channels are closed. Stage two, the energy of a stimulus triggers some blank voltage-gated ion channels to open, and blank ions diffuse into the axon cytoplasm. Stage three, more voltage-gated blank ion channels open, and more blank ions diffuse into the axon. Stage four, the potential difference across the membrane reaches plus 40 millivolts, and the voltage-gated blank ion channels close. Stage five, the potassium voltage-gated ion channels open, and potassium ions diffuse out of the axon. Stage six, more potassium ions diffuse out of the axon until the membrane is hyperpolarized. The potassium channels close.

There are two key elements whose positively charged ions regulate the stages of an action potential in an axon. These are potassium, represented here as pink circles, and sodium, represented here as green circles. While potassium ions do play an important role, it is the movement of sodium ions across the membrane of a neuron which is crucial for initiating and propagating an action potential.

This diagram is a simple representation of an axon membrane at rest, as described by statement one. During this stage of the action potential, sodium ions are actively pumped out of the axon cytoplasm into the extracellular space against their concentration gradient. In other words, they are being transported from an area of low concentration inside the axon to an area of high concentration outside. When a stimulus is present, as described in statement two, energy is released which causes some voltage-gated sodium ion channels to open.

Because there is a much higher concentration of sodium ions outside the axon than inside, sodium ions diffuse down their concentration gradient into the axon cytoplasm. This causes the inside of the axon to become more positively charged than the outside, so more voltage-gated sodium ion channels open and more sodium ions diffuse in, as described by statement three.

When a sufficient number of sodium ions have diffused into the axon for the potential difference across the membrane to reach plus 40 millivolts, the voltage-gated sodium ion channels close again, as described by statement four. This prevents further sodium ions from diffusing into the axon and allows the axon membrane to eventually return to its resting potential. We have therefore demonstrated that the element which should replace the gaps in the first four statements is sodium.

Join Nagwa Classes

Attend live sessions on Nagwa Classes to boost your learning with guidance and advice from an expert teacher!

  • Interactive Sessions
  • Chat & Messaging
  • Realistic Exam Questions

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy