from where "automaticity" of heart came?

cardiology medicine question.

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from cells that act like a bypass, those nodes r everywhere in the heart; they generate they own action potential by Ca++, K+, Na+. This potential is what makes the heart beat. systole and diastole. They dont need any stimulation from parasimpatic or simpatic systems. they activate by themselves.

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I am not quite sure what your question is so i will answer it based on what I think you are trying to ask. Automaticity deals with a region just above your heart between the superior vena cava and the right atrium (there are four chambers, ie. right atrium, left atrium, right ventricle, left ventricle. In a normally functioning heart, there is an area called the sino-atrial node which is normal area that fires an electrical impulse to induce normal rhythm and contraction of the heart. From the SA node, the electrical impulse fires down into the heart then spreads throughout the rest of the cardiac muscle to induce a normal beat. Typically it fires the impulse about 60 to 90 times per minute which allows the heart chambers to contract and push blood from the right atrium into the right ventricle then to the lungs to oxygenate the blood. From the lungs, the blood is then pumped into the left atrium and finally into the left ventricle where the blood is sent to the arteries of your body to oxygenate all tissues. However, in some cases as in diseased cardiac muscle, either the SA node doesnt fire consistently and when this happens another area of the heart will take over and become the electrical stimulator. In extreme circumstances, there may be several stimulator nodes which can cause irregular beats, skipped beats and premature contractions, causing the heart to be less efficient in getting oxygenated blood to the body tissues. That in a nutshell describes the "automaticity" of the heart. I hope this was helpful for you.
Regards,
Warren Shaffer, M.D.
Source(s):
www.familydoctor.org
www.webmd.org or com (cant remember which one)
www.aha.org
or do a search for "sino-atrial node" or "SA node of the heart".
You should be able to find in more detail what I was describing to you.
Good luck!

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Generally it comes from the Sino-Atrial node in the heart.the so-called pacemaker.

However, a more detailed explanation is as follows:
Cardiac cells have a membrane potential, which means electrically these cells have differing amounts of ions such as sodium (Na+), potassium(K+) Chloride(Cl-) and others. These special pacemaker cells have a rather unstable membrane potential compared to the rest of the heart (meaning it is not as negative as the others and is easy to depolarize). They lack the K+ inward rectifier channel that helps to further negatively polarize the membrane.

Also these cells begin to slowly depolarize over time. They have a slow but steady leak of Na+ ions inside which further depolarize the cell. The membrane slowly becomes less permeable to K+ which further prevents repolarization until Ca+ floods in and initiates a depolarization of the pacemaker cell which then causes depolarization of the surrounding cells and an overall transmission of a depolarization for the atrial cardiomyocytes to contract.

How exactly all the pacemaker cells coordinate with each other is still a bit of a mystery and how physiologial factors such as you running work to speed up the rate of depolarization at the molecular level is still under investigation. More can be found undoubtedly at http://www.pubmed.com/ if you search for terms such as "pacemaker potential" "sino-atrial node" etc

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AUTOMATICITYThe tissues in the conduction system and most of the myocardial cells have the ability to initiate an electrical impulse - a property known automaticity. Each area in the conduction system generates electric impulses at different rates.

The SA node, the primary pacemaker, generates impulses at a rate of 60-100 times per minute; the AV node 40-60 impulses per minute; and the ventricle at 20-40 impulses per minute. The further down the conduction system, the slower the pace maker at initiating impulses. If the SA node fails, the next fastest pacemaker - usually the AV node - maintains the heart rate and acts as backup to the system.

Heart Conduction System

The sinoatrial node (SAN), located within the wall of the right atrium (RA), normally generates electrical impulses that are carried by special conducting tissue to the atrioventricular node (AVN).

Upon reaching the AVN, located between the atria and ventricles, the electrical impulse is relayed down conducting tissue (Bundle of HIS) that branches into pathways that supply the right and left ventricles. These paths are called the right bundle branch (RBBB) and left bundle branch (LBBB) respectively. The left bundle branch further divides into two sub branches (called fascicles).

Electrical impulses generated in the SAN cause the right and left atria to contract first. Depolarization (heart muscle contraction caused by electrical stimulation) occurs nearly simultaneously in the right and left ventricles 1-2 tenths of a second after atrial depolarization. The entire sequence of depolarization, from beginning to end (for one heart beat), takes 2-3 tenths of a second.

All heart cells, muscle and conducting tissue, are capable of generating electrical impulses that can trigger the heart to beat. Under normal circumstances all parts of the heart conducting system can conduct over 140-200 signals (and corresponding heart beats) per minute.

The SAN is known as the "heart's pacemaker" because electrical impulses are normally generated here. At rest the SAN usually produces 60-70 signals a minute. It is the SAN that increases its' rate due to stimuli such as exercise, stimulant drugs, or fever.

Should the SAN fail to produce impulses the AVN can take over. The resting rate of the AVN is slower, generating 40-60 beats a minute. The AVN and remaining parts of the conducting system are less capable of increasing heart rate due to stimuli previously mentioned than the SAN.

The Bundle of HIS can generate 30-40 signals a minute. Ventricular muscle cells may generate 20-30 signals a minute.

Heart rates below 35-40 beats a minute for a prolonged period usually cause problems due to not enough blood flow to vital organs.

Problems with signal conduction, due to disease or abnormalities of the conducting system, can occur anyplace along the heart's conduction pathway. Abnormally conducted signals , resulting in alterations of the heart's normal beating, are called arrhythmias or dysrrythmia.

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from where "automaticity" of heart came?

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