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- 您请求的操作仅限于组中的用户:==功能改变的机制== ==== " '(a)去神经超敏感:" ' ====这种现象发生在皮质神经元丢失时。由于神经元受损，没有神经信号通过这些神经元。因此，为了弥补这一点，突触后膜产生了更多的神经递质受体来传递神经信号。这种突触后膜受体增加的现象导致其去神经支配阶段的超敏感。==== ''(b)长时程增强'' ====在这种现象中，在突触后膜上，有少量谷氨酸的释放。此外，这种谷氨酸与存在于细胞膜上的受体结合。这导致AMPA (α氨基-3-羟基-5-甲基4-异恶唑丙酸)受体的刺激，使钠(Na+)流入突触后膜。此外，镁离子被释放，随后阻断NMDA (n -甲基d -天冬氨酸)受体。总的来说，这个过程导致谷氨酸在突触后膜上进一步释放。因此，更多的钠离子进入突触后膜，增加了正电荷。 Furthermore, this event leads to expelling of magnesium ions from the NMDA receptors, which allows more calcium influx into the post-synaptic cells. All this leads to activation of ‘Protein Kinase C and Calmodulin Kinase’, which causes the addition of more AMPA receptors over the pos-synaptic membrane. This leads to further stimulation of post-synaptic membrane to release more glutamate which enhances ‘strengthening of the synapse and thus potentiation has occurred’ '''Properties of Long term potentiation''' '''(i) Cooperativity''': A presynaptic membrane should reach to a threshold to produce an impulse '''(ii) Specificity''': Long term potentiation can only be generated at one particular synaptic junction. However, the adjacent which is not activated cannot show long term potentiation '''(iii) Associativity''': There is a connection between the two adjacent synapses. In which stronger stimulus at one synapse can lead to the generation of impulse at a weaker synapse ==== '''(c) Long-term Depression''' ==== This long term depression follows the low-frequency stimulation of the post-synaptic membrane. In this process, the release of glutamate over the post-synaptic membrane leads to a lower level of depolarisation. This slow gradual stimulus leads to the passage of calcium through NMDA receptors, which gradually builds up the number of calcium ions at the receptor site. This process leads to activation of the ‘Phosphatases’ protein, which further dephosphorylates the substrate to maintain AMPA receptors to carry out generation or stimulation of the post-synaptic membrane. Therefore, leading to the generation of ‘Weaker post-synaptic response’ ==== '''(d) Synaptic strengthening''' ==== In this process, there occur structural changes in the synapse to facilitate neurotransmission. Basically this works on the ‘Hebbs Postulate’ in which coordinated activity of a presynaptic terminal and a postsynaptic membrane would make the synaptic connection stronger (‘Hebbian plasticity).
