Neural circuit

Neural circuit is a population of neurons interconnected by synapses to carry out a specific function when activated. Neural circuits interconnect to one another to form large scale brain networks.

The basic kinds of connections between neurons are synapses: both chemical and electrical synapses.

The establishment of synapses enables the connection of neurons into millions of overlapping, and interlinking neural circuits. Presynaptic proteins called neurexins are central to this process.

One principle by which neurons work is neural summation – potentials at the postsynaptic membrane will sum up in the cell body.

If the depolarization of the neuron at the axon hillock goes above threshold an action potential will occur that travels down the axon to the terminal endings to transmit a signal to other neurons.

Excitatory and inhibitory synaptic transmission is realized mostly by excitatory postsynaptic potentials, and inhibitory postsynaptic potentials.

An example of a neural circuit is the trisynaptic circuit in the hippocampus. Another is the Papez circuit linking the hypothalamus to the limbic lobe. There are several neural circuits in the cortico-basal ganglia-thalamo-cortical loop.

These circuits carry information between the cortex, basal ganglia, thalamus, and back to the cortex. The largest structure within the basal ganglia, the striatum, is seen as having its own internal microcircuitry.

Neural circuits in the spinal cord called central pattern generators are responsible for controlling motor instructions involved in rhythmic behaviours. Rhythmic behaviours include walking and urination. The central pattern generators are made up of different groups of spinal interneurons.

There are four principal types of neural circuits that are responsible for a broad scope of neural functions.

These circuits are a diverging circuit (one neuron synapses with a number of postsynaptic cells), a converging circuit (inputs from many sources are converged into one output, affecting just one neuron or a neuron pool), a reverberating circuit(produces a repetitive output. In a signalling procedure from one neuron to another in a linear sequence, one of the neurons may send a signal back to initiating neuron), and a parallel after-discharge circuit (after-discharge circuit, a neuron inputs to several chains of neurons).

Different neuroimaging techniques have been developed to investigate the activity of neural circuits and networks. The use of “brain scanners” or functional neuroimaging to investigate the structure or function of the brain is common, either as simply a way of better assessing brain injury with high resolution pictures, or by examining the relative activations of different brain areas.

Such technologies may include functional magnetic resonance imaging, brain positron emission tomography and computed axial tomography scans.

Functional neuroimaging uses specific brain imaging technologies to take scans from the brain, usually when a person is doing a particular task, in an attempt to understand how the activation of particular brain areas is related to the task.

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