depolarization

Examples of depolarization in the following topics:

• Nerve Impulse Transmission within a Neuron: Action Potential

  • Signals are transmitted from neuron to neuron via an action potential, when the axon membrane rapidly depolarizes and repolarizes.
  • Once the sodium channels open, the neuron completely depolarizes to a membrane potential of about +40 mV.
  • Once the threshold potential is reached, the neuron completely depolarizes.
  • As soon as depolarization is complete, the cell "resets" its membrane voltage back to the resting potential.
  • The action potential is conducted down the axon as the axon membrane depolarizes, then repolarizes.

• Synaptic Transmission

  • When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated Na+ channels.
  • Na+ ions enter the cell, further depolarizing the presynaptic membrane.
  • This depolarization causes voltage-gated Ca2+ channels to open.
  • When the presynaptic membrane is depolarized, voltage-gated Ca2+ channels open and allow Ca2+ to enter the cell.
  • 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.

• Excitation–Contraction Coupling

  • This reduces the voltage difference between the inside and outside of the cell, which is called depolarization.
  • As ACh binds at the motor end plate, this depolarization is called an end-plate potential.
  • The depolarization then spreads along the sarcolemma and down the T tubules, creating an action potential.

• Balance and Determining Equilibrium

  • The moving otolith layer, in turn, bends the sterocilia to cause some hair cells to depolarize as others hyperpolarize.
  • The exact tilt of the head is interpreted by the brain on the basis of the pattern of hair-cell depolarization .

• Signal Summation

  • Sometimes, a single excitatory postsynaptic potential (EPSP) is strong enough to induce an action potential in the postsynaptic neuron, but often multiple presynaptic inputs must create EPSPs around the same time for the postsynaptic neuron to be sufficiently depolarized to fire an action potential.

• Transduction and Perception

  • In the nervous system, a positive change of a neuron's electrical potential (also called the membrane potential), depolarizes the neuron.
  • If the magnitude of depolarization is sufficient (that is, if membrane potential reaches a threshold), the neuron will fire an action potential.

• Synaptic Plasticity

  • However, when the postsynaptic neuron is depolarized by multiple presynaptic inputs in quick succession (either from one neuron or multiple neurons), the magnesium ions are forced out and Ca2+ ions pass into the postsynaptic cell.
  • The next time glutamate is released from the presynaptic cell, it will bind to both NMDA and the newly-inserted AMPA receptors, thus depolarizing the membrane more efficiently.

• Reception and Transduction

  • Binding of an acid or other sour-tasting molecule triggers a change in the ion channel which increases hydrogen ion (H+) concentrations in the taste neurons; thus, depolarizing them.

• 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 .

• Nerve Impulse Transmission within a Neuron: Resting Potential

  • A nerve impulse causes Na+ to enter the cell, resulting in (b) depolarization.