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The undershoot phase occurs because unlike voltage-gated sodium channels, voltage-gated potassium channels inactivate much more slowly.Nevertheless, as more voltage-gated K channels become inactivated, the membrane potential recovers to its normal resting steady state..There are two families of receptors: ionotropic and metabotropic receptors.Ionotropic receptors are a combination of a receptor and an ion channel.Neurons are cells that are specialized to receive, propagate, and transmit electrochemical impulses.In the human brain alone, there are over eighty billion neurons.
There are several underlying mechanisms that cooperate to achieve synaptic plasticity, including changes in the quantity of neurotransmitters released into a synapse and changes in how effectively cells respond to those neurotransmitters.Synaptic plasticity in both excitatory and inhibitory synapses has been found to be dependent upon postsynaptic calcium release Two molecular mechanisms for synaptic plasticity (researched by the Eric Kandel laboratories) involve the NMDA and AMPA glutamate receptors.Opening of NMDA channels (which relates to the level of cellular depolarization) leads to a rise in post-synaptic Ca2 concentration and this has been linked to long-term potentiation, LTP (as well as to protein kinase activation); strong depolarization of the post-synaptic cell completely displaces the magnesium ions that block NMDA ion channels and allows calcium ions to enter a cell – probably causing LTP, while weaker depolarization only partially displaces the Mg2 ions, resulting in less Ca2 entering the post-synaptic neuron and lower intracellular Ca2 concentrations (which activate protein phosphatases and induce long-term depression, LTD).Some neurons such as photoreceptor cells, for example, do not have myelinated axons that conduct action potentials.
Other unipolar neurons found in invertebrates do not even have distinguishing processes such as dendrites.
In neuroscience, synaptic plasticity is the ability of synapses to strengthen or weaken over time, in response to increases or decreases in their activity.