Electrophysiology: What It Is And How It Is Investigated
Electrophysiology is responsible for analyzing and studying the electrical processes that occur in different organs, tissues and structures of our body, such as the heart, muscles or brain. Its application in clinical practice helps us observe and diagnose different pathologies and diseases.
In this article we explain what is electrophysiology and what the main techniques for recording electrical activity consist of.
Electrophysiology is the science that studies the electrical properties of the cells and biological tissue of an organism Although the best known study is that related to the cardiac system, measurements (such as the change in voltage or electrical current) can also be recorded in other types of body structures, such as muscles or the brain, through the use of electrodes that measure electrical activity.
In the mid-19th century, Italian physicist Carlo Matteuci was one of the first scientists to study electrical currents in pigeons. In 1893, the Swiss physiologist Wilhelm His, famous for being the founder of histology and inventor of the microtome (an instrument that allows biological tissue to be sectioned to be analyzed under a microscope), contributed new findings in cardiac electrophysiology. And already in 1932, Holzmann and Scherf discovered and invented the electrocardiogram.
Currently, Neuroscience is nourished by research and advances in new electrophysiological techniques that allow micro (from a simple ion channel) and macro (up to the entire brain) analysis of brain structures.
Advances in the knowledge of the functioning of behavior and the human nervous system are based on studies in which electrical signals from individual neurons and large-scale neuronal groups are recorded In neuropsychology, for example, we seek to explore the correlations between certain areas of the brain and higher cognitive functions or certain behaviors, which is why the electrical activity recording techniques used in electrophysiology are so important.
In electrophysiology, when we talk about the study of electrical properties we refer to the ion flux analysis (an atom or a group of them with an electrical charge, which can be positive or cation, and negative or anion) and to the state of rest and activity of excitable cells (neurons, cardiac cells, etc.).
The excitability of a cell is a property that allows them to respond actively to the application of a stimulus, that is, any energetic variation in the environment. These stimuli can be of multiple types: mechanical, thermal, sound, light, etc. For example, in neurons, this excitability gives them the ability to change its electrical potential to transmit that nervous impulse through the axon, to other neurons.
The membrane that covers the cell regulates the passage of ions from the outside to the inside, since they contain different concentrations of them. All cells have a potential difference between the inside and outside of the cell, called the membrane potential, which is due to the existence of ionic concentration gradients on both sides of the membrane, as well as differences in the relative permeability of the membrane. cell to the different ions present.
Furthermore, excitable cells exert their functions by producing electrical signals in terms of membrane potential changes, a key concept in electrophysiology. These electrical signals can be: brief and of great amplitude (such as action potentials), responsible for transmitting information quickly and over long distances; slower and lower voltage, with an integrating function; and low voltage (such as synaptic potentials), which originate through synaptic action.
Types of electrophysiological readings
The recording of electrical activity can occur in different biological tissues and cells, as well as with different electrophysiology techniques.
The most common electrophysiological recordings They include: electrocardiogram, electroencephalography and electromyography. Below, we explain in more detail what each of them consists of.
1. Electrocardiogram
The electrocardiogram (ECG) is an electrophysiology technique that is responsible for recording the electrical activity of the heart, through the study of voltage changes during a certain time (which usually does not exceed 30 seconds). A graph is usually recorded on the monitor, similar to a television screen, of the electrocardiograph.
The electrical activity of the heart that is recorded in the ECG can be observed in the form of a trace that presents different waves that correspond to the path of the electrical impulses through the different structures of the cardiac system.
This test is essential for the study of cardiac problems such as arrhythmias, heart disease or acute episodes in coronary heart disease such as myocardial infarction.
An ECG is performed as follows:
2. Electroencephalogram
An electroencephalogram (EEG) is an electrophysiology technique that allows detecting and recording the electrical activity of the brain, through small electrodes fixed on the person’s scalp. This test is non-invasive and is commonly used in neuroscience to observe and study the functioning of the central nervous system and, more specifically, the cerebral cortex.
With this technique, neurological alterations that suggest diseases such as epilepsy, encephalopathies, narcolepsy, dementia or neurodegenerative diseases can be diagnosed. In addition, the EEG also allows us to identify the normal and pathological rhythms of brain activity, as well as the waves that we usually have both when awake and during sleep: alpha, beta, delta, theta and gamma.
This test also It is frequently used in studies of sleep phases (polysomnography), to detect possible abnormalities in the recordings of rapid eye movement (REM) cycles and normal sleep cycles (NREM), as well as to detect other possible sleep disorders.
The EEG lasts approximately 30 minutes and can be performed in a hospital or neurophysiology unit. To perform it, the patient sits in a chair and the electrodes (between 15 and 25 sensors) are attached to the scalp, using a hair gel so that the electrical activity is recorded correctly. And while the person is relaxed, the test is performed.
3. Electromyogram
The electromyogram (EMG) is a procedure used to study the electrical activity of muscles and their nerve cells or motor neurons These neurons transmit electrical signals that produce muscle activity and contraction.
To perform an EMG, electrodes are needed that are placed on the muscles, either at rest or during exercise. To detect the muscle response, it is necessary to insert a small needle, which can sometimes be uncomfortable for the patient.
The only complication of this test is that a small bleeding may occur at the electrode insertion site, hence patients with a coagulation disorder or those undergoing anticoagulant treatment must be taken into account.
Another electrophysiology technique that sometimes accompanies EMG is electroneurography, which studies the speed of conduction of impulses through the nerves To do this, a nerve is stimulated with low-intensity electrical impulses, using sensors placed on the skin that collect the response from other sensors located at a distance, thus recording how long it takes for the response to occur when driving from one side to the other. .
