Neural backpropagation is when an impulse moves backwards through a neural circuit, causing depolarization of the cell body and potentially changing cell firing properties. It is regulated by ion channels and is associated with synaptic plasticity and learning.
Neural backpropagation is the name given to the phenomenon of an impulse moving backwards through a neural circuit. While action potentials usually travel from the cell—starting specifically at the axon hillock point—down the axon to terminal buttons that form synapses with recipient cells, an action potential that propagates backwards it actually moves backwards by diffusion of incoming ions, causing voltage-gated ion channels to open the axon instead of lowering it. Usually, neural backpropagation has a short range of effects, but has the potential to travel through an entire neural circuit.
An action potential in a neuron is initiated at the axon hillock, which is where the axon meets the soma of a neural cell. Most neurons have a single axon that can fork many times. This neurite is the process that sends out signals from the cell, while dendrites, which are the other neurites on a neuron, are commonly processes that receive signals. Neural backpropagation is regulated by ion channels in the axon and on the cell body.
An axon functions in its role of conducting action potentials from the axon mound to the axon’s terminal points, called terminal buttons, by opening channels in the axonal membrane that allow positively charged ions into the cell, depolarizing it and causing voltage-gated channels to open. Voltage-gated channels allow more positively charged ions into the cell, such as calcium and potassium. When a cell loses its -70mV resting potential and depolarizes due to the positive charges of incoming ions, it “fires” and releases neurotransmitter-filled vesicles from terminal buttons at the end of an axon.
Signal propagation works like ion channels along an axon causing other nearby channels to open, but this signal propagation can move in the reverse direction and when it does, it is referred to as neural back propagation. This process occurs when an action potential is initiated at the axon hillock and, while it might proceed along the axon as usual, it also conducts a signal in the opposite direction, causing depolarization of the cell body, including synapses and segments of neighboring dendrites. When a dendritic segment is depolarized, the postsynaptic densities located within that region respond differently to incoming signals from other neurons. Some possible consequences of neural backpropagation include phenomena such as dendro-dendritic inhibition and a change in membrane potential, which can change cell firing properties.
Synaptic plasticity such as long-term potentiation (LTP) and long-term depression (LTD) are associated with neural backpropagation because a backpropagation signal modifies incoming signals. While the concept may seem elementary, the notion of future behavior change based on past experience is one possible definition of learning. In one sense, then, one could say that neural backpropagation allows individual cells to “learn” at the molecular level. Neural backpropagation is often seen in the neocortex, hippocampus, and other brain regions often associated with memory, learning, or a high degree of neural plasticity.
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