The of the synapse gives rise toThe of the synapse gives rise to

The EEG is a recording of the
electrical activity in the brain. It results from the activity of large
populations of neurons. There are three ways in which a signal is measured:
Action potentials along axons of neurones, currents through synapses which
connect axons with neurons and finally, currents along dendrites from the
synapse to the neurone. The electrical activity arises from the cortical
neurons in the brain which generates electrical currents which spread
throughout the head. These currents spread to the surface of the scalp where
they are detected by the electrodes in the form of voltage changes. The
physiological basis behind an EEG signal can be explained by considering the
electrical activity of the single pyramidal cell activated by an afferent
pathway. The incoming signal of the synapse gives rise to a postsynaptic
potential resulting from the positive charged ions rushing into the cell. As
this current propagates down the conductive dendron of the neurone the size of
the EPSP decreases. This leaves a relatively negative charge in the
extracellular space immediately surrounding the synapse. This creates a dipole
with separation of charge wontedly orientated in the cortex. Every neuron that
receive somatic inputs can therefore be thought as a dipole with specific
orientation and polarity. Signals cannot be detected from single neurons as the
potentials are very small magnitude and on a cellular scale are considered
distance from cell to scalp surface. The signal detected is the summation of
all the titles created at each on the thousand neurons. Hyperventilation
triggers “typical” seizures and is performed by the child during EEGs which
explains why Kaden also suffered an attack when asked to hyperventilate.

 

EEGs are measured using the International
Federation 10-20 system. In preparation, 21 silver-silver electrodes are placed
at specific anatomical points on the head of the patient. A differential signal
is amplified and sprayed as a channel of EEG activity. Montage is the
representation of the EEG channels and there are many types: Bipolar (which is
the difference between two adjacent electrodes), common reference (difference
between one electrode and a common electrode) and finally average reference
(activity from all electrodes summed and averaged and then used as a reference
electrode.

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