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6 Electric and Magnetic Fields in Life
6.5.2 Electrophysiology
Intracellular Electrophysiology
To investigate electrical activity within individual biological cells, a microprobe can
be constructed as a glass pipette containing an ionic fluid or a chlorided silver wire,
and tapered to a size smaller than the cell. The probe is inserted into the live cell.
The circuit is completed by a second probe or silver plate in contact with an ionic
extracellular solution. The strength of the electric field and variations in the electric
potential across the cell wall are measurable. For nerve cells, these variations can be
as large as 100 mV.
Electroencephalography
An electroencephalograph (EEG) is a recording of the electrical activity on the skin
on skull. That activity reflects the synchronous electric field of a large number of
neurons firing near the surface of the brain, i.e. the cortex. Such activity can show
the presence of epileptic seizures, as well as states of sleep or thinking. Skin voltages
are in the range of 10–100 μV, and have characteristic frequencies from a few cycles
per second to greater than 100 Hz. The activity of individual cells requires alternate
methods, such as neural probes inserted or electrodes implanted into the brain.
Electrocardiography
Electrocardiology is the study of the electric activity of the heart. An electrocardiogram is a device for measuring and recording that activity. Our heart pulse is
regulated by nerve impulses. The electrical activity of the heart can be monitored by
small electrically conducting pads placed on the chest.
An electrocardiogram (ECG or, from the German, EKG) records the electrical
activity of the heart by measuring the cutaneous electric potential across the
thorax. When the muscle cells of the heart electrically depolarize, they contract.
During normal heart beating, the heart muscle cells of the atrium of the heart are
stimulated to contract in unison by the electrical activity of the sinoatrial node. The
depolarization synchronously spreads quickly to the right atrium and then to the
ventricles. The voltage changes involved cause a change in the electric field on the
skin of the thorax surrounding the heart. These changes are detectable by sensitive
voltmeters, and produce typically voltages of 0.1–15 mV. Atrial depolarization can
be seen as a rise and fall in voltage over a time of about an eighth of a second,
producing what is called the ‘P’ wave. The ventricular depolarization produces
the ‘QRS’ wave. The ‘Q’ and ‘S’ parts are voltages opposite to the atrial initial
voltage, with ‘S’ usually stronger than‘ Q’, while the ‘R’ part is a strong positive
voltage spike (much larger than that of the ‘P’-wave). Following the ‘QRS’ wave,
a small ‘T’ wave can be seen, which is cause by the ventricular re-polarization
6 Electric and Magnetic Fields in Life
6.5.2 Electrophysiology
Intracellular Electrophysiology
To investigate electrical activity within individual biological cells, a microprobe can
be constructed as a glass pipette containing an ionic fluid or a chlorided silver wire,
and tapered to a size smaller than the cell. The probe is inserted into the live cell.
The circuit is completed by a second probe or silver plate in contact with an ionic
extracellular solution. The strength of the electric field and variations in the electric
potential across the cell wall are measurable. For nerve cells, these variations can be
as large as 100 mV.
Electroencephalography
An electroencephalograph (EEG) is a recording of the electrical activity on the skin
on skull. That activity reflects the synchronous electric field of a large number of
neurons firing near the surface of the brain, i.e. the cortex. Such activity can show
the presence of epileptic seizures, as well as states of sleep or thinking. Skin voltages
are in the range of 10–100 μV, and have characteristic frequencies from a few cycles
per second to greater than 100 Hz. The activity of individual cells requires alternate
methods, such as neural probes inserted or electrodes implanted into the brain.
Electrocardiography
Electrocardiology is the study of the electric activity of the heart. An electrocardiogram is a device for measuring and recording that activity. Our heart pulse is
regulated by nerve impulses. The electrical activity of the heart can be monitored by
small electrically conducting pads placed on the chest.
An electrocardiogram (ECG or, from the German, EKG) records the electrical
activity of the heart by measuring the cutaneous electric potential across the
thorax. When the muscle cells of the heart electrically depolarize, they contract.
During normal heart beating, the heart muscle cells of the atrium of the heart are
stimulated to contract in unison by the electrical activity of the sinoatrial node. The
depolarization synchronously spreads quickly to the right atrium and then to the
ventricles. The voltage changes involved cause a change in the electric field on the
skin of the thorax surrounding the heart. These changes are detectable by sensitive
voltmeters, and produce typically voltages of 0.1–15 mV. Atrial depolarization can
be seen as a rise and fall in voltage over a time of about an eighth of a second,
producing what is called the ‘P’ wave. The ventricular depolarization produces
the ‘QRS’ wave. The ‘Q’ and ‘S’ parts are voltages opposite to the atrial initial
voltage, with ‘S’ usually stronger than‘ Q’, while the ‘R’ part is a strong positive
voltage spike (much larger than that of the ‘P’-wave). Following the ‘QRS’ wave,
a small ‘T’ wave can be seen, which is cause by the ventricular re-polarization