hyperpolarization

Examples of hyperpolarization in the following topics:

• The Action Potential and Propagation

  • First is depolarization, followed by repolarization and a short period of hyperpolarization.
  • Hyperpolarization is a phase where some potassium channels remain open and sodium channels reset.
  • This results in hyperpolarization as seen in a slight dip following the spike.

• Transduction of Light

  • Thus, unlike most other sensory neurons (which become depolarized by exposure to a stimulus), visual receptors become hyperpolarized and are driven away from the threshold .
  • Exposure of the retina to light hyperpolarizes the rods and cones, removing the inhibition of their bipolar cells.
  • As a result, the membrane becomes hyperpolarized.
  • The hyperpolarized membrane does not release glutamate to the bipolar cell.

• Nerve Impulse Transmission within a Neuron: Action Potential

  • The diffusion of K+ out of the cell hyperpolarizes the cell, making the membrane potential more negative than the cell's normal resting potential.
  • Eventually, the extra K+ ions diffuse out of the cell through the potassium leakage channels, bringing the cell from its hyperpolarized state back to its resting membrane potential.
  • At the same time, Na+ channels close. (4) The membrane becomes hyperpolarized as K+ ions continue to leave the cell.
  • The hyperpolarized membrane is in a refractory period and cannot fire. (5) The K+ channels close and the Na+/K+ transporter restores the resting potential.

• Neurotransmitters

  • Inhibitory neurotransmitters cause hyperpolarization of the postsynaptic cell (that is, decreasing the voltage gradient of the cell, thus bringing it further away from an action potential), while excitatory neurotransmitters cause depolarization (bringing it closer to an action potential).
  • The depolarizing (more likely to reach an action potential) or hyperpolarizing (less likely to reach an action potential) effect is also dependent on the receptor.
  • However, when acetylcholine binds to the muscarinic receptor, it might cause depolarization or hyperpolarization of the target cell.
  • Glycine and GABA are considered inhibitory amino acids, again because their receptors cause hyperpolarization, making the receiving cell less likely to reach an action potential.

• Postsynaptic Potentials and Their Integration at the Synapse

  • When the opening of the ion channels results in a net gain of negative charge, the potential moves further from zero and is referred to as hyperpolarization.

• Agonists, Antagonists, and Drugs

  • Gi-protein activation also leads to the activation of KACh channels that increase potassium efflux and hyperpolarizes the cells.
  • By hyperpolarizing the cells, vagal activation increases the cell's threshold for firing, which contributes to the reduction the firing rate.

• Synaptic Transmission

  • The neurotransmitter diffuses across the synaptic cleft and binds to ligand-gated ion channels in the postsynaptic membrane, resulting in a localized depolarization or hyperpolarization of the postsynaptic neuron.

• Balance and Determining Equilibrium

  • The moving otolith layer, in turn, bends the sterocilia to cause some hair cells to depolarize as others hyperpolarize.

• Membrane Potentials as Signals

  • This is called a depolarization if the interior voltage becomes more positive (say from –70 mV to –60 mV), or a hyperpolarization if the interior voltage becomes more negative (say from –70 mV to –80 mV).

• Nerve Impulse Transmission within a Neuron: Resting Potential

  • At the peak action potential, K+ channels open and the cell becomes (c) hyperpolarized.