Last update:

Postsynaptic Neuron Resting Membrane Potential

  • When a postsynaptic neuron is at rest (not “firing”), its membrane is polar-ized, meaning the interior is slightly more negative than the exterior.
  • The polarity is referred to as the resting membrane potential (or RMP) and is due primarily to the unequal distribution of Na+, K+, and protein ions along the surfaces of the membrane.
  • Na+ and K+ ions are actively moved to opposite sides of the postsynaptic membrane by image descriptionNa+/K+ pump proteins.
An image showing the stabilizing action potential of a neuron cell membrane
An image showing the stabilizing action potential of a neuron cell membrane
1
2
  • Each pump protein uses one molecule of ATP to image descriptiontransfer 3 Na+ ions out of the cell and 2 K+ ions in.
  • As a result, Na+ ions are concentrated outside the postsynaptic membrane and K+ ions are concentrated inside the membrane. The opposing ion gradients created by the pumps are nearly equal and contribute only slightly to the RMP.
  • Very few of the Na+ ions can diffuse back into the resting cell because most of the image descriptionNa+ channels are closed.
An image showing the stabilizing action potential of a neuron cell membrane
An image showing Na channels of a neuron cell membrane which is enlarged
1
2
  • The conditions are different for the K+ ions. The postsynaptic membrane contains many image descriptionleak channels that allow K+ ions to freely exit the cell.
An image showing Na channels of a neuron cell membrane which is enlarged
An image showing K+ leaking channels and Na channels of a neuron cell membrane which is enlarged
1
2
  • The image descriptionoutward diffusion of K+ ions makes the interior of the membrane more negative and the exterior more positive, which significantly alters the RMP. Also contributing to the growing polarity are a large number protein anions that are confined within cell.
  • An image descriptionequlibrium is quickly reached between the outward diffusion gradientĀ for K+ and the inward electrical gradient.
An image showing K+ leaking channels and Na channels of a neuron cell membrane which is enlarged
An image showing the equilibrium of the K+ leaking channel of a neuron cell membrane
1
2