Where does the source of heartbeat control come from?

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In summary, the brain does not initiate heartbeat, but it does have control over the rate through the autonomic nervous system. The SA node at the top of the heart sets the pace, but the medulla in the brain stem can release adrenaline into the bloodstream to increase sympathetic activity, which can influence the heart rate. However, the heart is still an autonomous organ and can function without input from the brain. Defibrillation is used to temporarily stop the heart in certain rhythms, in the hopes that it will return to a normal rhythm after the shock. The mechanism for controlling heart rate involves a unique membrane channel in the SA node that spontaneously depolarizes after hyperpolarization.
  • #1
Johninch
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I thought that the brain, specifically the medulla in the lower brain stem, controls heatbeat. But according to what I am reading, heartbeat is caused by electrical impulses in the heart which cause the heart muscles to contract. What is the source flow of this electricity? Does it come from the medulla, or does the medulla only regulate the pulse when there is already a pulse?

In the case of sudden cardiac arrest, defillibration is applied to the heart directly. Is there then a feedback from the heart to the medulla causing it to adjust its heatbeat commands? What exactly causes the electrical activity of the heart to become irregular?

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  • #2
Johninch said:
I thought that the brain, specifically the medulla in the lower brain stem, controls heatbeat. But according to what I am reading, heartbeat is caused by electrical impulses in the heart which cause the heart muscles to contract. What is the source flow of this electricity? Does it come from the medulla, or does the medulla only regulate the pulse when there is already a pulse?

In the case of sudden cardiac arrest, defillibration is applied to the heart directly. Is there then a feedback from the heart to the medulla causing it to adjust its heatbeat commands? What exactly causes the electrical activity of the heart to become irregular?

.

In a healthy heart, it is the Sinus Node at the top of the heart that sets the pace:

http://www.nhlbi.nih.gov/health/health-topics/topics/hhw/electrical.html

When the Sinus Node malfunctions, the AV Node will generally set the pace, albeit slower than the normal sinus rhythm.
 
  • #3
berkeman said:
In a healthy heart, it is the Sinus Node at the top of the heart that sets the pace:

http://www.nhlbi.nih.gov/health/health-topics/topics/hhw/electrical.html

When the Sinus Node malfunctions, the AV Node will generally set the pace, albeit slower than the normal sinus rhythm.

Thanks, a very good animation!

Meantime I made some progress concerning the function of the Medulla. It seems that the Medulla can release adrenaline into the bloodstream which increases overall sympathetic activity, including being received by adrenoceptors at the Sinus Node. Thus the Sinus Node is influenced by the brain to increase heartbeat, but the brain does not initiate heartbeat. In this sense, the heart is autonomous.

If this is correct, the only piece of my question which I am now missing is the mechanism which causes the Sinus Node to malfunction.

.
 
  • #4
Johninch said:
Thanks, a very good animation!

Meantime I made some progress concerning the function of the Medulla. It seems that the Medulla can release adrenaline into the bloodstream which increases overall sympathetic activity, including being received by adrenoceptors at the Sinus Node. Thus the Sinus Node is influenced by the brain to increase heartbeat, but the brain does not initiate heartbeat. In this sense, the heart is autonomous.

If this is correct, the only piece of my question which I am now missing is the mechanism which causes the Sinus Node to malfunction.

.

There are a number of things that can cause the SA node to stop firing regularly. A Google search on Sinus Node Malfunction gives a number of helpful links. Here is one of them:

http://emedicine.medscape.com/article/158064-overview

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  • #5
Thanks. It seems that the answer to my question "What controls heartbeat?" is as follows:

The Wiki entry on the Autonomic Nervous System (ANS), which is located in the Medulla Oblongata in the brain stem, explains that the Sympathetic and Parasympathetic nervous systems have excitory and dampening effects respectively on various organs including the heart. There is a neuron pathway via ganglions from the Medulla to the heart (and to other organs). Sympathetic ganglionic neurons release noradrenalin and other transmitters such as ATP at the end synapses, which act on adrenergic receptors at the SA Node, AV Node and heart muscles. This increases the heart rate when necessary for fight or flight actions or for other movements which would otherwise result in a fall in blood pressure.

Thus it seems to be confirmed that, although the heart is an autonomous organ, the rate of heartbeat is determined by the brain, provided the Medulla Oblongata is working. If this part of the brain is out of action, the heart may continue to function at a normal frequency, assuming that the lungs are also working. The purpose of CPR and defillibration is to maintain minimum heart and lung action, in the case that they have been disturbed, in order to delay tissue death, brain damage and other problems, until the ANS can resume its normal heartbeat control function.

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  • #6
Mostly right, but the heart rate is usually set by the SA node, and *modified* by the sympathetic and parasympathetic systems.

The purpose of CPR is as you described, to provide pumping action to keep blood circulating and perfusing the body. The purpose of defibrillation is to temporarily stop the heart when it is in certain (bad) rhythms, in the hope that the heart will return to a better rhythm after the shock.
 
  • #7
Its a membrane channel of the SA node cells that causes a current called If (channel is called the funny channel or HCN)- that spontaneously depolarizes after hyperpolarization that sets heart rate - the CNS then only acts as a modifier of the intrinsic rate of the SA node by modifying the rate of depolarization caused by If by changing the activity of this channel. So heart rate is set by a type of membrane channel that is quite unusual in its activation!
 

1. What is the main organ responsible for controlling heartbeat?

The main organ responsible for controlling heartbeat is the heart itself. More specifically, it is the sinoatrial (SA) node, also known as the "pacemaker" of the heart, that controls the heartbeat by generating electrical impulses.

2. How does the SA node control the heartbeat?

The SA node is a small cluster of specialized cells located in the right atrium of the heart. It generates electrical impulses that spread throughout the heart and stimulate the heart muscles to contract and relax, resulting in a regular heartbeat.

3. What factors can affect the SA node and disrupt the heartbeat?

The SA node can be affected by various factors such as hormones, nerve signals, and electrolyte imbalances. Certain medications, diseases, and lifestyle habits like smoking, excessive alcohol consumption, and stress can also disrupt the SA node and cause irregular heartbeats.

4. Can the heartbeat be controlled voluntarily?

No, the heartbeat is controlled involuntarily by the autonomic nervous system. This means that we cannot consciously control or change the rate or rhythm of our heartbeat. However, certain relaxation techniques like deep breathing and meditation can indirectly influence the heartbeat by calming the body and reducing stress levels.

5. Can the heart continue to beat without the SA node?

Yes, in some cases, the heart can continue to beat without the SA node. This is because other cells in the heart also have the ability to generate electrical impulses and take over as the pacemaker. However, this can result in an irregular heartbeat and may require medical treatment to restore a normal rhythm.

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