Postsynaptic potential
Postsynaptic potentials are changes in the
The role of ions
One way receptors can react to being bound by a neurotransmitter is to open or close an ion channel, allowing ions to enter or leave the cell. It is these ions that alter the membrane potential. Ions are subject to two main forces,
Relation to action potentials
Neurons have a resting potential of about −70 mV. If the opening of the ion channel results in a net gain of positive charge across the membrane, the membrane is said to be depolarized, as the potential comes closer to zero. This is an excitatory postsynaptic potential (EPSP), as it brings the neuron's potential closer to its firing threshold (about −55 mV).
If, on the other hand, the opening of the ion channel results in a net gain of negative charge, this moves the potential further from zero and is referred to as hyperpolarization. This is an inhibitory postsynaptic potential (IPSP), as it changes the charge across the membrane to be further from the firing threshold.
Neurotransmitters are not inherently excitatory or inhibitory: different receptors for the same neurotransmitter may open different types of ion channels. [3]
EPSPs and IPSPs are transient changes in the membrane potential, and EPSPs resulting from transmitter release at a single synapse are generally far too small to trigger a spike in the postsynaptic neuron. However, a neuron may receive synaptic inputs from hundreds, if not thousands, of other neurons, with varying amounts of simultaneous input, so the combined activity of afferent neurons can cause large fluctuations in membrane potential or subthreshold membrane potential oscillations. If the postsynaptic cell is sufficiently depolarized, an action potential will occur. For example, in low-threshold spikes depolarizations by the T-type calcium channel occur at low, negative, membrane depolarizations resulting in the neuron reaching the threshold. Action potentials are not graded; they are all-or-none responses.
Termination
Postsynaptic potentials begin to be terminated when the neurotransmitter detaches from its receptor. The receptor is then free to return to its previous structural state. Ion channels that had been opened by the receptor when the neurotransmitter was bound to it will now close. Once the channels are closed, ions return to their equilibrium states, and the membrane is returned to its equilibrium potential.
Algebraic summation
Postsynaptic potentials are subject to summation, spatially and/or temporally.
See also
- Action potential
- Electrophysiology
- Goldman equation
- Membrane potential
- Nernst equation
- Neuron
- Neurotransmission
- Postsynaptic
- Synapse
- End-plate potential
External links
- Postsynaptic+Potentials at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
References
- ^ Henley, Casey (2021-01-01). "Postsynaptic Potentials".
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- PMC 4458710.