Basic component of bioelectrical signals Caused by the flow of
Na +, K + and Cl - ions across the cell membrane
Slide 4
Resting potential: In their resting state, the membrane readily
permit the entry of K + and Cl - ions, but effectively block the
entry of Na + ions. The permeability of membrane for K + is 50-100
times that for Na + ions. A cell in resting state is said to be
polarized. The resting potential is in order of -60 to -100 mV
Slide 5
Slide 6
Depolarization: When a cell is excited the membrane changes its
characteristics and begins to allow Na + ions to enter the cell.
This movement of Na + ions constitutes an ionic current, which
further reduces the membrane barrier to Na + ions. This leads to an
avalache effect: Na + ions rush into the cell. The inside of the
cell becomes positive. The peak value of action potential is about
20 mV
Slide 7
Repolarization: Membrane depolarization also increases the
permeability of membrane for K + ions via a voltage-dependent K +
channels. The permeability of membrane for Na + ions decrease near
the peak of depolarization. The efflux of K + ions from the cell
makes the inside more negative thereby effecting repolarization
back to the resting potential. Duration in nerve and muscle cells
~1 ms, in heart muscle cells 150-300 ms
Slide 8
All-or-none phenomenon Absolute refractory period: 1 ms in
nerve cells Relative refractory period: several ms in nerve
cells
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The ENG is an electrical signal observed as a stimulus and the
associated nerve action potential propagate over the length of
nerve. ENGs may be recorded using contcentric needle electrodes or
Ag-AgCl electrodes at the surface of the body. In order to minimize
muscle contraction strong but short stimulus is applied (100 V
amplitude, 100-300 s). ENGs have amplitudes of the order of 10
V.
Slide 12
Wirst BElbow - below the elbow AElbow above the elbow
Slide 13
Typical values of propagation rate or nerve conduction velocity
are: 45-70 m/s in nerve fibers 0.2-0.4 m/s in heart muscle
0.03-0.05 m/s in time delay fibers between the atria and
ventricles. Neural diseases may cause a decrease in conduction
velocity.
Slide 14
Motor units Single Motor Unit Action Potential (SMUAP)
Slide 15
Normal SMUAPs are usually biphasic or triphasic 3-15 ms in
duration, 100- 300 V in amplitude, 6-30 Hz in frequency range
Slide 16
The 10-20 system of electrode placement for EEG recording.
Slide 17
The commonly used terms for EEG frequency range: Delta (0.5-4
Hz): deep sleep Theta (4-8 Hz): beginning stages of sleep Alpha
(8-13 Hz): principal resting rhythm Beta (>13 Hz): background
activity in tense and anxious subjects
The electrical activity of the stomach consists of rhytmic
waves of depolarization and repolarization of its constituent
smooth muscle cells. The activity originates in the mid-corpus of
the stomach, with intervals of about 20 s in human. Recorded by
abdomen electrodes e.g. three electrodes along the antral axis of
stomach and the common reference electrode
Slide 20
The CP is a pressure signal recorded over the carotid artery.
Parts of CP: P (percussion wave): ejection of blood from the left
ventricle T (tidal wave): reflected pulse from the upper body D
(dicrotic notch): closure of the aortic valve DW (dicrotic wave):
reflected pulse from the lower body
Slide 21
Direct mechanical manifestation of contraction of a skeletal
muscle. Accompanies the EMG Recorded by contact microphones or
accelerometers placed on the muscle surface.
Slide 22
The VAG is the vibration signal recorded from a joint during
movement (articulation) of the joint. Normal joint surfaces are
smooth and produce little or no sound. Joint affected by
osteoarthiritis and other degnereative diseases may have suffered
cartilage loss and produce grinding sounds. The VAG is complex
signal and difficult to analyze.
