Sodium-Potassium Pump
The Sodium-Potassium Pump is an essential biological structure that the neuron has in order to function. To stabilize its inside and outside balance at the resting state, in addition to changing to an action potential state, is all due to the sodium-potassium pump. To help maintain a negative membrane potential, this process requires ATP to bring 3 sodium ions to the outside of the cell, and 2 potassium ions to the inside of the cell. The pump starts off in a cell environment that is more positively charged on the outside than on the inside. On both sides of the neuron, are scattered potassium and sodium ions. From the inside, 3 sodium ions bind to the pump. ATP (cell’s energy) is then used to break down further into ADP and phosphates to alter the shape of the pump. The pump, now facing the outside, releases the 3 sodium ions to the outside, in which 2 potassium ions now bind to the pump. The pump changes shape again, releasing the potassium ions back into the cell. In conclusion, the neuron ends up with more sodium on the outside, and more potassium on the inside. In a 3:2 ratio of sodium ions going outside and potassium ions going inside, the potential difference is more positive on the outside. The main cause of this positivity on the outside is because of the cell membrane’s tendency to be more permeable to potassium ions rather than sodium ions.
Electrotonic and Action Potentials
A neuron in its resting state signifies the voltage difference across the cell membrane. The higher concentration of sodium ions on the outside is because of the sodium-potassium pump. Two types of potentials enable the neuron to spread a signal passively, and provides a boost for the signal to shoot across the distance the length covers. The first is electrotonic spread, which is the spread of electrotonic potential. This type of potential is passive and dissipates across the length of the membrane. This is due to the diffusion of sodium ions on the outside to the inside of the membrane. The second is action potential. For the same purpose, a stimulus will create a depolarization current, and when this current reaches -55mV, an action potential is fired. In addition, depolarization is the electrical change within a cell, which results in a less negative charge inside the cell.
Credit: Khan Academy Nervous System Intro. All entries are written by Jadon-Sean Sobejana
