Poly Electronic Theory Wk 1-2 Ch 1,

Poly Electronic Theory wk 1-2 ch 1, ch 2 , ch 5, ch 9

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Frequency
Frequency of a wave is characterized by the number of times it repeats or oscillates in a second.
Measured in Hertz or cycle per second (cps)
A wave that oscillates 3 times in one second (or makes 3 complete upward and downward motions) has a frequency of 3 Hz.
Waves that look wide are slow and have a low frequency.
Amplitude
Amplitude of a wave is directly affected by the voltage of the of the associated signal. When sensitivity and gain settings are identical, a taller wave is derived from a higher voltage signal than a shorter wave.
Hertz
Measured in Hertz or cycle per second (cps)
A wave that oscillates 3 times in one second (or makes 3 complete upward and downward motions) has a frequency of 3 Hz.
Time Constant
Also, Fall time or Fall time constant defined as the amount of time for a calibration wave to fall from its highest point or peak to 37% of its peak.
Time Constant performs the same function as the low frequency filter in that they both place limits on the amt of slow wave activity displayed by attenuating (decrease) the amplitude of the signals with frequencies below the filter settings.
Rise time
Defined as the amt of time it takes for the calibration wave to reach 63% of its peak, which is a very short time (usually in the hundredths of a second).
Rise time of a calibration wave increases and decreases with the HFF setting.
Conversely, a decreased LFF setting allows slower waves to enter the signal which causes the calibration wave to fall more slowly. Therefore, a decreased LFF setting increases the time constant.
Action Potential Overview
A potential, or electrical voltage, always exist between the inside and outside of a cell
the potential of an inactive cell is ALWAYS NEGATIVE
An action Potential is a rapid swing in the polarity of the membrane potential from NEGATIVE TO POSITIVE and back
The entire cycle lasts a FEW MILLISECONDS
Action Potentials
Physiologic electrical activity is based on the concentration of and flow of ions across the cell membrane.
Transmembrance Potential is based on the concentration of ionic charges
inside the cell compared to charges outside the cell
Action Potentials
When activated sodium channels open from an instant increasing sodium permeability
Positively charged sodium ions diffuse inward across the negatively charged cell membrane
The cell membrane momentarily becomes Positive
Action Potentials
The sodium channels close quickly and potassium channels open briefly
Potassium channels diffuse outward and inside of membrane returns to Negative
The Brain
In Poly the head is used as a signal source.
All bio-electric activity is based on the concentration and flow of ions across the cellular membrane
This trans-membrane potential is based on the concentration of ions (charges) inside the cell to those outside the cells
Local Potentials of the Brain
Are responsible for EEG (Electroencephalogram) signals
IPSP (inhibitory Post Synaptic Potential)- inhibits neuron from firing
EPSP (Excitatory Post Synaptic Potential)- causes the neuron to fire causing action potential
We measure a large grouping of these cells in order to get an EEG signal
Bio-Electric Activity
Changes in electrical potential recorded from a point on the scalp come from a summation of membrane potentials
It is NOT recording the activity of individual neurons in the brain
It IS recording the synchronously occurring post-synaptic potentials of thousands of neurons
BRAIN
Electrical Potentials from the brain are grouped into two categories
Slow potentials
Fast potentials
Differential amplifiers are used for EEG recordings
CARDIAC
The cardiac action potential is the electrical activity of the individual cells of the electrical conduction system of the heart
These are responsible for the recording of EKG (electrocardiogram)
Muscle
The action potential of muscles activates the calcium ion on the axon and calcium rushes in
This will cause the axon to fuse with the membrane- releasing acetyl-choline