Otis Singleton
An electrical impulse refers to the flow of electricity generated by specific cells in the heart's electrical system, which triggers the contraction of the heart muscles. These cells, known as pacemaker cells, have the ability to spontaneously generate electrical signals, initiating the heart's rhythmic activity. As you read these words, billions upon billions of electrical impulses are flying through your brain. These impulses are generated by the sinus node (also called the sinoatrial node, or SA node), which is a small mass of specialized tissue located in the right upper chamber (atria) of the heart.
| Characteristics | Values |
|---|---|
| Definition | An electrical impulse refers to the flow of electricity generated by specific cells in the heart's electrical system, which triggers the contraction of the heart muscles. |
| Cells responsible | Pacemaker cells |
| Location of pacemaker cells | Sinus node, cells responsible for atrial conduction, area immediately above the atrioventricular (AV) node, low portion of the AV node, His bundle, and Purkinje ventricular system |
| Rate of electrical stimulus | 60 to 100 times per minute under normal conditions |
| Direction of electrical impulse | From the sinus node to the AV node, then into the ventricles |
| Conduction pathways | Right and left bundle branches of Purkinje fiber |
| Mechanism of origination | 1. Automaticity 2. Re-entry |
| Role in the brain | Electrical impulses encode thoughts and are involved in information processing |
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What You'll Learn
Electrical impulses in the brain
The electrical impulses in the brain are generated by certain cells in the brain's electrical system, which have the ability to spontaneously generate electrical signals. These cells are known as pacemaker cells and are found in the sinus node, the cells responsible for atrial conduction, the area above the atrioventricular (AV) node, the lower portion of the AV node, the His bundle, and the Purkinje ventricular system. The sinus node, or sinoatrial (SA) node, acts as the primary pacemaker, generating the normal rhythmic impulse.
The process of myelination, or insulation, speeds up communication among brain cells. Neurons are more efficient conductors of electrical impulses if they are covered with an insulating material called myelin. The amount of myelin coating on neurons is influenced by mental activity, with neglected children having less myelin in certain brain regions and animals raised in stimulating environments having increased myelin production. Myelination also appears to be influenced by the learning process, with activities such as learning to play the piano fostering myelination.
The study of electrical impulses in the brain has been challenging due to the difficulty in observing the activity of individual neurons within larger circuits. Traditional methods, such as inserting an electrode into the brain, are labour-intensive and only allow for the recording of activity from one neuron at a time. More advanced techniques, such as multielectrode arrays and calcium imaging, have been developed to monitor electrical activity from multiple neurons simultaneously.
Recently, researchers have engineered a molecule called Archon1, which can be genetically inserted into neurons and fluoresces brighter when neuronal electrical activity increases. This molecule has been used to image electrical activity in the brains of transparent worms, zebrafish embryos, and mouse brain slices. By modifying the probe, researchers were able to use it in living, awake mice as they engaged in specific behaviours, providing valuable insights into the functioning of the brain.
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Electrical impulses in the heart
The heart is a pump made of muscle tissue. Its pumping action is regulated by electrical impulses, which trigger heartbeats. These electrical impulses are generated by specific cells in the heart's electrical system, known as pacemaker cells. These cells have the ability to spontaneously generate electrical signals, initiating the heart's rhythmic activity.
Pacemaker cells are found in the sinus node, in the cells responsible for atrial conduction, in the area immediately above the atrioventricular (AV) node, in the lower portion of the AV node, in the His bundle, and in the Purkinje ventricular system. The sinus node, or sinoatrial (SA) node, acts as the primary pacemaker, generating the normal rhythmical impulse. The electrical impulse flows from the sinus node to the AV node, then to the ventricles. The left and right bundle branches of Purkinje fiber conduct the cardiac impulse to all parts of the ventricles. Each time the impulse completes a circuit, the heart beats.
The electrical impulses in the heart can be too slow, causing a decrease in heart rate, known as bradycardia. This can be caused by heart block, where the electrical signal cannot get through from the upper to the lower chambers of the heart. Alternatively, the impulses can be abnormally fast, a condition called tachycardia. In many cases of tachycardia, there is an extra electrical path in addition to the normal path, which can be either separate from or within the AV node. This extra pathway allows the electrical impulse to make a continuous loop, resulting in a very rapid heartbeat.
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How electrical impulses are generated
An electrical impulse refers to the flow of electricity generated by specific cells in the heart's electrical system, which triggers the contraction of the heart muscles. These cells, known as pacemaker cells, have the ability to spontaneously generate electrical signals, initiating the heart's rhythmic activity.
Pacemaker cells are found in the sinus node, in the cells responsible for atrial conduction, in the area immediately above the atrioventricular (AV) node, in the low portion of the AV node, in the His bundle, and in the Purkinje ventricular system. The sinus node or sinoatrial (SA) node, in which the normal rhythmical impulse is generated, has the highest rate of spontaneous depolarization and acts as the primary pacemaker.
There are two basic mechanisms related to the origination of an electrical impulse in the myocardium. The first is automaticity, where the impulse is generated through the mechanism of automaticity. The second is re-entry, where the basic components of the re-entry mechanisms include two conduction pathways, one of which has unidirectional locking (or a long refractory period), and the other has slow conduction.
Neurons conduct electrical impulses by using the Action Potential. This phenomenon is generated through the flow of positively charged ions across the neuronal membrane. Neurons, like all cells, maintain different concentrations of certain ions (charged atoms) across their cell membranes. They pump out positively charged sodium ions and pump in positively charged potassium ions. Thus, there is a high concentration of sodium ions present outside the neuron and a high concentration of potassium ions inside.
The neuronal membrane also contains specialized proteins called channels that form pores in the membrane that are selectively permeable. When the sodium channels are opened, positively charged sodium ions flood into the neuron, making the inside of the cell momentarily positively charged - the cell is said to be depolarized. This has the effect of opening the potassium channels, allowing potassium ions to leave the cell. Thus, there is first an influx of sodium ions (depolarization) followed by a rapid efflux of potassium ions (repolarization). This cycle of depolarization and repolarization is extremely rapid, taking only about 2 milliseconds (0.002 seconds), thus allowing neurons to fire action potentials in rapid bursts, a common feature in neuronal communication.
In Functional Electrical Stimulation (FES), small electrical impulses are applied to the nerves that supply the affected muscles using either self-adhesive electrodes placed on the skin or implanted electrodes on the nerve or muscle. The electrical current generates an electric field between the pair of electrodes, and, with the right conditions, may induce a nerve impulse that is propagated along the nerve to the muscle, causing the muscle to contract in a manner very similar to natural contraction.
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How electrical impulses are conducted
An electrical impulse refers to the flow of electricity generated by specific cells in the heart's electrical system, which triggers the contraction of the heart muscles. These cells, known as pacemaker cells, have the ability to spontaneously generate electrical signals, initiating the heart's rhythmic activity.
The cells that make up the electrical system of the heart are responsible for the formation of the electric current and the conduction of this impulse to the contractile cells of the myocardium, where the depolarization activates the contraction. The internodal pathways conduct the impulse from the sinus node to the AV node. The AV bundle conducts the impulse from the atria into the ventricles, and the left and right bundle branches of Purkinje fiber conduct the cardiac impulse to all parts of the ventricles.
Neurons also conduct electrical impulses. They do this by using the Action Potential, which is generated through the flow of positively charged ions across the neuronal membrane. Neurons, like all cells, maintain different concentrations of certain ions (charged atoms) across their cell membranes. They pump out positively charged sodium ions and pump in positively charged potassium ions. This creates a high concentration of sodium ions outside the neuron and a high concentration of potassium ions inside.
The neuronal membrane also contains specialised proteins called channels, which form pores in the membrane that are selectively permeable to particles. When the sodium channels are opened, positively charged sodium ions flood into the neuron, making the inside of the cell momentarily positively charged. This is known as depolarization. Depolarization, in turn, opens the potassium channels, allowing potassium ions to leave the cell. Thus, there is first an influx of sodium ions (depolarization) followed by a rapid outflow of potassium ions (repolarization). This cycle of depolarization and repolarization is extremely rapid, taking only about 2 milliseconds (0.002 seconds) and thus allows neurons to fire action potentials in rapid bursts, a common feature in neuronal communication.
Myelin, the fatty membranes of cells, acts as an insulator, preventing the dissipation of the depolarization wave. The sodium and potassium ion channels, pumps, and other equipment associated with action potential propagation are concentrated at sites between blocks of myelin called the Nodes of Ranvier. This myelin sheath allows the action potential to jump from one node to another, greatly increasing the rate of transmission.
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Electrical impulses in the body
In the heart, electrical impulses originate in the atria, the upper chambers, and then pass to the ventricles, causing them to contract. This process is regulated by pacemaker cells, which have the ability to spontaneously generate electrical signals and initiate rhythmic activity. The sinus node, or sinoatrial (SA) node, acts as the primary pacemaker, generating the normal rhythmic impulse.
The electrical impulses in the heart can be mapped to understand and treat heart conditions. For example, in the case of atrioventricular nodal reentrant tachycardia, electrical impulses circle back immediately via a rogue pathway, causing constant signals for the ventricles to contract. This results in a rapid heart rate and can be treated with procedures like ablation.
Additionally, electrical impulses are crucial for movement. They are generated by certain cells and transmitted through neurons, resulting in muscle contractions. This process can be artificially induced through electrical stimulation, such as in the case of treating muscle conditions with Functional Electrical Stimulation (FES).
Beyond movement and heart function, electrical impulses are also vital for brain signalling. The body's nervous system conducts electrical charges using ions, primarily potassium and sodium ions, which pass through neurons. By understanding and interpreting these electrical signals, scientists aim to predict and treat illnesses, such as inflammatory bowel disease (IBD).
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Frequently asked questions
An electrical impulse is a flow of electricity generated by specific cells in the heart's electrical system, which triggers the contraction of the heart muscles.
Electrical impulses in the brain are individual jolts of electricity that travel along neurons. These impulses are often described as looking like "spikes" or "trees".
Electrical impulses in the heart are generated by the sinus node, which creates an electrical stimulus that travels through the conduction pathways, causing the heart's ventricles to contract and pump out blood.
