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username3835832
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In my a level text book is says with electrocardiograms, ''a bigger wave means more electrical charge, so a bigger wave means more contraction.''
I thought contraction means depolarization so loss of electrical charge?
I thought contraction means depolarization so loss of electrical charge?
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Jpw1097
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(Original post by chemquestion)
In my a level text book is says with electrocardiograms, ''a bigger wave means more electrical charge, so a bigger wave means more contraction.''
I thought contraction means depolarization so loss of electrical charge?
In my a level text book is says with electrocardiograms, ''a bigger wave means more electrical charge, so a bigger wave means more contraction.''
I thought contraction means depolarization so loss of electrical charge?
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2007PSanHa
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Polarisation is when the electrical charge inside and outside of a cell becomes further apart.
Depolarisation is when the electrical charge inside and outside of a cell becomes closer together.
The bigger the ECG wave the larger the change in charge between the inside and outside of the cell.
I think this is right. Hope it makes sense!
Depolarisation is when the electrical charge inside and outside of a cell becomes closer together.
The bigger the ECG wave the larger the change in charge between the inside and outside of the cell.
I think this is right. Hope it makes sense!
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macpatgh-Sheldon
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Hi,
I think sometimes an attempt at simplification introduces error.
The author of your A level book is probs a biologist, not a doctor. Jpw1097 has provided a completely correct summary of how the ECG works, but might be too detailed for an A level student.
I would simplify it for you thus:-
Think physics for the moment (GCSE level will do): charge refers to STORED electrical energy (measured in coulombs) -electrical activity, effectively current, only occurs when there is change in charge through movement of electrons.
The y axis on an ECG is in mV (millivolts) i.e. potential difference or voltage, which is proportional to current for a fixed system (i.e. if resistance is constant). So it is the voltage level that is manifested by a positive or negative deflection on the ECG, NOT charge.
As JPW says, the total MOVEMENT of electrical activity of all the muscle cells of the heart (Greek: cardio = of heart; myo = muscle; cytos = cell) produces the deflections on the ECG. For A level purposes, just remember that the greater the muscle volume, the taller the R wave (in general ONLY) e.g. a patient with e.g. longstanding essential hypertension (=high blood pressure) will have an enlarged heart and his/her ECG will have taller R waves in certain leads to put it simply (a lead is one recording that "looks" at the heart from a particular direction - there are 12 leads in a standard ECG).
Try and remember only this much - ignore the book on this point!
M (former medical student)
I think sometimes an attempt at simplification introduces error.
The author of your A level book is probs a biologist, not a doctor. Jpw1097 has provided a completely correct summary of how the ECG works, but might be too detailed for an A level student.
I would simplify it for you thus:-
Think physics for the moment (GCSE level will do): charge refers to STORED electrical energy (measured in coulombs) -electrical activity, effectively current, only occurs when there is change in charge through movement of electrons.
The y axis on an ECG is in mV (millivolts) i.e. potential difference or voltage, which is proportional to current for a fixed system (i.e. if resistance is constant). So it is the voltage level that is manifested by a positive or negative deflection on the ECG, NOT charge.
As JPW says, the total MOVEMENT of electrical activity of all the muscle cells of the heart (Greek: cardio = of heart; myo = muscle; cytos = cell) produces the deflections on the ECG. For A level purposes, just remember that the greater the muscle volume, the taller the R wave (in general ONLY) e.g. a patient with e.g. longstanding essential hypertension (=high blood pressure) will have an enlarged heart and his/her ECG will have taller R waves in certain leads to put it simply (a lead is one recording that "looks" at the heart from a particular direction - there are 12 leads in a standard ECG).
Try and remember only this much - ignore the book on this point!
M (former medical student)
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