Long-term Potentiation

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Long-Term Potentiation (LTP) is the process by which repetitive stimulation at a synapse increases the efficiency of transmission at that synapse. This process depends on the diffusion of calcium ions through NMDA receptors. Neurotransmitter glutamate diffuses across synaptic cleft and it binds to two inotropic receptors. The AMPA receptor is a sodium ion channel and so triggers an EPSP. Depending on what modulation is going on in that cell body, the EPSP may or may not trigger an action potential. The NMDA receptor is blocked by magnesium ions and so has no effect, however, repetitive stimulation results in greater depolarization and magnesium ion is ejected from the NMDA receptor. This enables calcium ions flow through the NMDA receptor, it is the diffusion of calcium ions cause the postsynaptic cell to become more sensitive to glutamate and enhances glutamate release from the presynaptic cell [1]. If only LTP is expressed at synapses, they would be of limited value as an information storage device as they would become saturated. Synapses also exhibit long-term depression (LTD) which also requires the activation os the NMDA receptor and a rise in Ca2+. The magnitude in the rise  in Ca2+ determines the bidirectional control of synaptic strength. Hig Ca2+ levels activate LTP, whereas modest Ca2+ levels activate LTD. [2]

References

  1. Bruce Alberts et al (2008) Molecular Biology Of The Cell, 5th edition, Garland Science Taylor and Francis Group
  2. Bruce Alberts et al (2008) Molecular Biology Of The Cell, 5th edition, Garland Science Taylor and Francis Group
 
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