Need help ASAP. Only have 20 mins.

The human heart beats day and night without a person giving much thought to the intricate process. How is the impulse generated? Describe the generation of the impulse (through the heart) including the anatomical features of the heart that are involved. Relate the impulse movement through the heart with the stages of the cardiac cycle.

Answer:

Human heart is basically an autoregulatory organ. It depends on the depolarization of SA node which acts as a pacemaker for the heart. SA node have a a highly sensitive membrane potential which undergoes self depolarization by reaching the threshold potential on its own.

Now talking about the Impulse generation.

Impulse generation or action potential generation is one and the same thing. it is a process which is divided in phase 1 phase 2,phase3,phase 4,

phase 1 . the resting membrane potential is -70 mv in the SA node when at -70 mv the sodium channels gets open which results in the increase in the membrane potential upto the threshold which is -40 mv.

phase 2- the rapid depolarizaton of potential takes place due to opening of the calcium channel for a long time which results the potential to be slightly above 0.

phase 3. this results in the opening of the potassium channel which results in the efllux of potassium causing quiick repolarization resulting in the getting back of the repolarized state.

phase4. the membrane potential again starts to increase due to the leakage of sodium ions which cause the potential to reach the threshold value.

and the cycle continues.

now this action potential generated is passed to the av node and then bundle of his and then to purkinjje fibres which are further distributed in the whole heart causing the contraction of the heart.

this 1 cycle takes place in 0.8secs which is equal to the cardiac cycle that is there is a relationship between the cardiac cycle and the AP generation.

when the AP is generated it travels through the coducting system and causes ventricular systole in response for 0.3secs and then this AP travels to the auricles which causes further contraction of auricles which takes place in 0.1sec and simultaneosly the the ventricles undergoes relaxation.

After this the auricles also go for a relaxation.

The ventricular relaxation takes 0.5sec and the auricular relaxtion takes 0.7sec of the cardiac cycle.

together they are in relaxation for 0.4secs. this is called the joint diastole again waiting for the new impulse from the SA node to get contracted.