The P wave is caused by electrical potentials generated when the atria depolarize before an atrial contraction begins. The QRS complex is caused by potentials generated when the ventricles depolarize before contraction—that is, as the depolarization wave spreads through the ventricles.
Therefore, both the P wave and the components of the QRS complex are depolarization waves. The T wave is caused by potentials generated as the ventricles recover from depolarization. This process normally occurs in ventricular muscle 0. The T wave is known as a repolarization wave. Thus, the ECG is composed of both depolarization and repolarization waves. The principles of depolarization and repolarization are discussed in Chapter 5.
The distinction between depolarization waves and repolarization waves is so important in electrocardiography that further clarification is necessary.
Figure shows a single cardiac muscle fiber in four stages of depolarization and repolarization, with the color red designating depolarization. During depolarization, the normal negative potential inside the fiber reverses and becomes slightly positive inside and negative outside. In Figure A, depolarization, demonstrated by red positive charges inside and red negative charges outside, is traveling from left to right.
The first half of the fiber has already depolarized while the remaining half is still polarized. Therefore, the left electrode on the outside of the fiber is in an area of negativity, and the right electrode is in an area of positivity, which causes the meter to record positively. To the right of the muscle fiber is shown a record of changes in potential between the two electrodes, as recorded by a highspeed recording meter.
Note that when depolarization has reached the halfway mark in Figure A, the recording on the right has risen to a maximum positive value. In Figure B, depolarization has extended over the entire muscle fiber, and the recording to the right has returned to the zero baselines because both electrodes are now in areas of equal negativity. The completed wave is a depolarization wave because it results from the spread of depolarization along the muscle fiber membrane.
Figure C shows halfway repolarization of the same muscle fiber, with positivity returning to the outside of the fiber. At this point, the left electrode is in an area of positivity, and the right electrode is in an area of negativity.
This polarity is opposite to the polarity in Figure 2A. Consequently, the recording, as shown to the right, becomes negative. In Figure D, the muscle fiber has completely repolarized, and both electrodes are now in areas of positivity so that no potential difference is recorded between them. Thus, in the recording on the right, the potential returns once more to zero. This completed negative wave is a repolarization wave because it results from the spread of repolarization along the muscle fiber membrane.
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Calcular el volumen de un cono. Calcular el volumen de una esfera. Ver menos Reconoce un cubo. Un cubo es una forma tridimensional que tiene seis caras cuadradas iguales. Halla la longitud de un lado del cubo.
Aprende a identificar un cilindro. Halla el radio de la base. Mide el objeto si no se te da el radio. Si no lo son, vuelve a revisarlas.
Halla la altura del cilindro. Aprende las propiedades de un cono. Para hacer esto, tienes que saber el radio de la base, el cual debe figurar en el diagrama. En el ejemplo del diagrama, el radio de la base circular del cono es de 7,5 cm 3 pulgadas. Halla la altura del cono. En nuestro ejemplo, la altura del cono es de 12 cm 5 pulgadas. Identifica a una esfera. Una esfera es un objeto tridimensional perfectamente redondo en el que cada punto de la superficie se encuentra a igual distancia del centro.
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