Lecture 11 Origin of Biopotentials

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Lecture 11Origin of Biopotentials
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Outline of topics

• Review ECG polar / magnetic /auto diagnosis
• Class ECG measurement instructions
• Cell membrane
• Nernst equation
• Membrane model
• Action potential in heart
• Action potential in nerves
• Biphasic measurements
• EEG, EMG
• polar / magnetic / autodiagnosis

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Cell wall and ion concentrations
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Membrane ion channels
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Nernst Equation
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Calculation of membrane voltage
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Comments on sodium pump

• Large molecule that penetrates membrane
• Few needed
• Theory predicts the chararcteristics but not yet
  observed directly
• pumps Na to outside using energy
• Gives with membrane C a battery effect
• K and Chloride concentrations follow

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Solution to membrane circuit(note currents are
ions, not electrons)
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continued
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Dynamic change in ions resistances
Hodgkin-Huxley
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Resistance changes
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Action potential
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Heart action potential
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Current flow near axons
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Bioelectric signals

• ECG / EKG
• EOG (eye movement) /ERG (retina)
• EEG
• EMG
• EAG
• ENG

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Eye Anatomy
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EOG/ERG
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Brain Anatomy
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EEG normal (note uv)
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EEG examples
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EEG awake to deep sleep
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EEG Electrode locations
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EEG notes and comments

• Small signal need good contacts and high S/N
  amplifier
• Lots of connections implantable types
• Look for differences between sides
• Not much information-but new studies show
  movement patterns can be extracted
• Evoked potentials
• Nerve conduction
• Freq plane anesthethology
• Dynamic displays - movies

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EMG - examples
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EMG notes and comments

• Used to determine if muscle activated normally
• Used to measure coordination between muscles
• Poor relation of EMG to force
• Reverse stimulation of muscles
• Eye movement looks at EMG of ocular muscles

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Summary

• Origin of biopotentials is in membrane
  concentration differences