Electrical activity of cells, tissues and organs

Electrical Biosignals

 Electrical activity of cells, tissues and organs 

What is Electrical Activity?

Electrical activity or electrophysiology is the study of the electrical properties of biological cells, tissues and organs. It is a branch of physiology that deals with the electrical phenomena relating nervous and other bodily activities. It includes measurements of change in voltage or electric current on a far-ranging variety of scales from single ion channel proteins to entire organs like the heart. In neuroscience, it involves measurements of the electrical activity of neurons and action potential activity.

 Nerve Impulses- Electricity in the body 

Human electrical energy is generated by chemical processes in nerve cells. Billions of nerve impulses travel throughout the human brain and nervous system. A nerve impulse is a wave of electrical activity that passes from one end of nerve cell to another. Each impulse is the same size that carries information about the intensity of the nerve signal. Neurons, basic unit of nervous system, are responsible for sending, receiving, and interpreting information from all parts of the body.

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Our body is a complex and carefully-balanced superhighway of cells, tissues and fluids that direct an incomprehensible array of electrical impulses almost every second. This is only possible due to a homeostatic environment where electricity is well conducted to carry the signals to their intended destinations. They key to maintaining this conductive superhighway lies within the ELECTROLYTES. Electrolytes regulate our nerve and muscle function, our body’s hydration, blood pH, blood pressure and the rebuilding of damaged tissues. Various mechanisms exist in our body that keep the concentrations of different electrolytes under strict control.

 Examples of Electrical Activities & principles  http://uni-em.com/wp-content/themes/uniem/i/products/cardiomin-2k.jpg
 * Electro-cardiogram (ECG) - ECG is a transthoracic interpretation of the electrical activity of the heart over time captured and externally recorded by skin electrodes.
 * Electroencephalogram (EEG) - EEG is the recording of electrical activity along the scalp produced by the firing of neurons within the brain.
 * Magnetoencephalogram (MEG) - MEG is a technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using arrays of SQUIDS (Superconduction Quantum Interference Devices).
 * Electromyogram (EMG) - EMG is a technique for evaluating and recording the electrical activity produced by skeletal muscles.

 Electrical Activity of Cells 

One of the simplest physiological units is the cell. It has the power of maintaining itself alive, being the smallest structural and functional unit of an organism, given suitable surroundings. Animal and plant cells consist of many molecular structures that are electrically responsive. The cell is often described as a miniature electrical factory.
 * Glucose-induced electrical activities - Diabetes mellitus or diabetes is a chronic metabolic disease which could be either insulin insufficient (type 1) or insulin resistant (type 2). Insulin insufficiency and impairment in pancreatic islet β-cells is also found combined with insulin resistance in type 2 diabetes. The cause of Insulin insufficiency is generally considered to be a result of β-cell damage by autoimmunity. Glucose stimulated insulin secretion is associated with a complex electrical activity in the pancreatic islet β-cell, which is characterized by a slow membrane depolarization superimposed with bursts of action potentials. Closing adenosine triphosphate (ATP)-sensitive K+ channels (KATP) in response to glucose increase is generally considered the initial event that depolarizes the β-cell membrane and activates the voltage-dependent Ca2+ channels, leading to the increase in intracellular Ca2+ that triggers the release of insulin. The β-cells become electrically active in glucose concentrations known to produce insulin secretion. The type of electrical activity depends on glucose concentration.

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 Electrical Activity of Organs  The functions of the brain depend on the ability of neurons to transmit electrochemical signals to other cells, and their ability to respond appropriately to electrochemical signals received from other cells. Neurotransmitters are chemicals that are released at synapses when an action potential activates them. They then attach themselves to receptor molecules on the membrane of the synapse's target cell, and thereby alter the electrical or chemical properties of the receptor molecules. With few exceptions, each neuron in the brain releases the same chemical neurotransmitter at all the synaptic connections it makes with other neurons; this rule is known as Dale’s Principle.
 * Brain - an organ of soft nervous tissue contained in the skull of vertebrates, functioning as the coordinating centre of sensation and intellectual and nervous activity.

As a side effect of the electrochemical processes used by neurons for signaling, brain tissue generates electric fields when it is active. When large numbers of neurons show synchronized activity, the electric fields that they generate can be large enough to detect outside the skull, using electroencephalography  (EEG)undefinedor magnetocephalography (MEG). During an epileptic seizure, the brain's inhibitory control mechanisms fail to function and electrical activity rises to pathological levels, producing EEG traces that show large wave and spike patterns not seen in a healthy brain.

The heart constantly generates a sequence of electrical activity with every single heart beat. This can be recorded on paper or displayed on a monitor by attaching special electrodes to a machine that can amplify and record an EKG or ECG (electrocardiogram). Note how the chambers of the heart contract when  they are electrically stimulated. This in turn makes the heart valves open and shut.
 * Heart - a hollow muscular organ that pumps the blood through the circulatory system by rhythmic contraction and dilation.

https://courses.kcumb.edu/physio/ecg%20primer/normecg1.GIF

The heart muscle is made of tiny cells. Its electrical system controls the timing of your heartbeat by sending an electrical signal through these cells.Two different types of cells in your heart enable the electrical signal to control your heartbeat: The electrical signal travels through the network of conducting cell "pathways," which stimulates your upper chambers (atria) and lower chambers (ventricles) to contract. The signal is able to travel along these pathways by means of a complex reaction that allows each cell to activate one next to it, stimulating it to "pass along" the electrical signal in an orderly manner. As cell after cell rapidly transmits the electrical charge, the entire heart contracts in one coordinated motion, creating a heartbeat.
 * Conducting cells carry your heart's electrical signal.
 * Muscle cells enable your heart's chambers to contract, an action triggered by your heart's electrical signal.

The electrical signal starts in a group of cells at the top of your heart called the sinoatrial (SA) node. The signal then travels down through your heart, triggering first your two atria and then your two ventricles. In a healthy heart, the signal travels very quickly through the heart, allowing the chambers to contract in a smooth, orderly fashion.

The heartbeat happens as follows: This cycle of an electrical signal followed by a contraction is one heartbeat.
 * The SA node (called the pacemaker of the heart) sends out an electrical impulse.
 * The upper heart chambers (atria) contract.
 * The AV node sends an impulse into the ventricles.
 * The lower heart chambers (ventricles) contract or pump.
 * The SA node sends another signal to the atria to contract, which starts the cycle over again.

 Importance in Clinical Medicine 
 * An Electrolyte imbalance can be manifested in several ways. The symptoms will depend on which electrolyte is out of balance. An altered level of magnesium, sodium, potassium, or calcium may produce one or more of the following symptoms:
 * 1) Irregular heartbeat
 * 2) Weakness
 * 3) Blood pressure changes
 * 4) Seizures
 * 5) Nervous system disorders

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 * A device which measures electrical activity in the brain is called EEG. Electroencephalography (EEG) is an electrophysiological monitoring method to record electrical activity of the brain. It is typically noninvasive, with the electrodes placed along the scalp, although invasive electrodes are sometimes used in specific applications. EEG measures voltage fluctuations resulting from ionic current within the neurons of the brain. In clinical contexts, EEG refers to the recording of the brain's spontaneous electrical activity over a period of time,undefinedas recorded from multiple electrodes placed on the scalp. With every good thing comes a bad. EEG causes low spatial resolution on the scalp, it poorly measures neural activity that occurs below the upper layers of the brain (the cortex). Unlike PET and MRS, it cannot identify specific locations in the brain at which various neurotransmitters, drugs, etc can be found.
 * The electrocardiogram (ECG or EKG) is a noninvasive test that is used to reflect underlying heart conditions by measuring the electrical activity of the heart. An EKG shows the heart’s electrical activity as line tracings on paper. The spikes and the dips are called waves. A natural electrical system causes the heart muscle to contract. This pumps blood through the heart to the lungs and the rest of the body.

- An EKG is done to:
 * Check the heart's electrical activity.
 * Find the cause of unexplained chest pain or pressure. This could be caused by a  heart attack or an inflammation of the sac surrounding the heart. However, the EKG is a static picture and may not reflect severe underlying heart problems at a time when the patient is not having any symptoms. Many abnormal patterns on an EKG may be non-specific, meaning that they may be observed with a variety of different conditions.

Bioelectricity has many effects other than the hazards discussed here. Devices such as pacemakers and defibrillators have saved countless lives. The measurement of the electrical characteristics and electrical activity of the human body have proved essential in ECG, EEG and other techniques. The uses of electricity and electromagnetic effects in healthcare are immense and are only going to grow in the future.

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