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Bioelectricity exam summary
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NotesLecture 1
-Bioelectromagnetism is a discipline that examines the electric, electromagnetic, and
magnetic phenomena which arise in biological tissues.
-ECG: Recordings of the electrical activity of the heart ,Non-invasive:
electrodes placed on the body andUsed for monitoring the patient’s
health
-Electrical impedance tomography (EIT): Measurement of
bioimpedance to produce a map (image) of impedance or changes
of impedance across a region, non-invasive and used for monitoring
of the brain function, detecting and localising tumors
-Cells exhibit a voltage difference across their membrane
-when there are bioelectric fields there always are also biomagnetic fields, and vice versa (Maxwell
equation).
-Nerve and muscle cells are excitable and the impulse propagates
along them in the same manner
-receive signals from other neurons (afferent) , conducts nerve
impulses (efferent)
-Electrical conduction: along the neuron (via ion channels) and Chemical conduction:
between neurons (via neurotransmitters) the ways nerve impulses are transmitted
-Membrane voltage (Vm = Φi-Φo) ,Resting: − 70 to − 90 mV
-Response to stimulus graded vs action potential
,-If the magnitude does not exceed the threshold, the response will be nonpropagating
(electrotonic). If the response is great enough, a nerve impulse (action potential impulse) will
be produced which obeys the all-or-nothing law
-Rheobase current: smallest current adequate to initiate activation (sensitivity)
Chronaxy: time needed to excite the cell with twice the rheobase current (speed of response)
strength-duration curve
+
-The concentration of sodium ions (Na ) is about 10 times higher outside the membrane than inside,
+
whereas the concentration of the potassium (K ) ions is about 30 times higher inside as compared to
outside.
-Once activation has been initiated, the membrane is insensitive to new stimuli, no matter how large
the magnitude. This phase is called the absolute refractory period. Near the end of the activation
impulse, the cell may be activated, but only with a stimulus stronger than normal. This phase is called
the relative refractory period.
-A myelinated axon (surrounded by the myelin sheath) can produce a nerve impulse only at
the nodes of Ranvier. In these axons the nerve impulse propagates from one node to anothe
-If depolarisation exceeds – 60mV, the cell ‘fires’ an AP.
-Size and shape of AP are independent of the of the stimulus.
Lecture 2
-Membrane at resting state: Slightly permeable to Na+ Highly permeable to K+ and Cl-
-Nernst eq. Equilibrium potential for a specific ion
-The principle whereby ions flow from regions of high to low concentration is called diffusion.
-The Nernst equation is derived from two basic concepts involving ionic flow - those resulting from
an electric field force and those resulting from a diffusional force.
, -
-Flow of ions through the membrane does not depend on the presence of other ions
Lecture 3
-The sodium potassium pump moves ions in and out of the membrane against the
electromotive force.
-The length constant is a measure of the distance from the site of stimulation over which
a significant response is obtained.
-The time constant is a measure of the time it takes for the signal to reach its maximum
value.
- goal is to measure selectively the flow of each constituent ion of the total membrane current.
-Space clamp: With appropriate instrumentation, it is possible to stimulate the axon simultaneously
throughout the entire length of the preparation. Elimination of the axial currents by keeping the
voltage same along the axial space
-Voltage clamp: The capacitive component can be eliminated by keeping the membrane voltage
constant during the measurement. Such a procedure is called voltage clamp. Elimination of the
capacitive current
-Series of voltage clamps:At a certain voltage the membrane voltage is at zero meaning
the system is at eq. for a specific ion. For instance at 52 mv it is the nernst voltage of Na
and at this Na is at equilibrium. So we have current only due to the potassium and we
ignore the leakage current.
-Slide 16because we oushed the voltage up now the Vna and membrane voltage Vm
has tha same value and Vm-Vna=0 so electromotive force 0 meaning there is no ion
movement
-How much chance in ionic conductances? Hodgkin – Huxley K+ and Na+ conductance
model (how channels open and close Na-K)
- Hodgkin and Huxley developed a method to quantitatively describe how ionic conductances
change during activation.
-Conductance of ions at rest are constant
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