Cathode rays or electron beams (e-beam) are streams of electrons observed in discharge tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow, due to electrons emitted from the cathode. They were first observed in 1859 by German physicist Julius Plücker and Johann Wilhelm Hittorf, and were named in 1876 by Eugen Goldstein Kathodenstrahlen, or cathode rays. In 1897, British physicist J. J. Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, which was later named the electron. Cathode-ray tubes (CRTs) use a focused beam of electrons deflected by electric or magnetic fields to render an image on a screen.
Magnetoencephalography (MEG) is a functional neuroimaging technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using very sensitive magnetometers. Arrays of SQUIDs are currently the most common magnetometer, while the SERF magnetometer is being investigated for future machines. Applications of MEG include basic research into perceptual and cognitive brain processes, localizing regions affected by pathology before surgical removal, determining the function of various parts of the brain, and neurofeedback. This can be applied in a clinical setting to find locations of abnormalities as well as in an experimental setting to simply measure brain activity.
The sucrose gap technique is used to create a conduction block in nerve or muscle fibers. A high concentration of sucrose is applied to the extracellular space, which prevents the correct opening and closing of sodium and potassium channels, increasing resistance between two groups of cells. It was originally developed by Robert Stämpfli for recording action potentials in nerve fibers, and is particularly useful for measuring irreversible or highly variable pharmacological modifications of channel properties since untreated regions of membrane can be pulled into the node between the sucrose regions.
Bioelectromagnetics, also known as bioelectromagnetism, is the study of the interaction between electromagnetic fields and biological entities. Areas of study include electromagnetic fields produced by living cells, tissues or organisms, the effects of man-made sources of electromagnetic fields like mobile phones, and the application of electromagnetic radiation toward therapies for the treatment of various conditions.
Biomagnetism is the phenomenon of magnetic fields produced by living organisms; it is a subset of bioelectromagnetism. In contrast, organisms' use of magnetism in navigation is magnetoception and the study of the magnetic fields' effects on organisms is magnetobiology.
Low field NMR spans a range of different nuclear magnetic resonance (NMR) modalities, going from NMR conducted in permanent magnets, supporting magnetic fields of a few tesla (T), all the way down to zero field NMR, where the Earth's field is carefully shielded such that magnetic fields of nanotesla (nT) are achieved where nuclear spin precession is close to zero. In a broad sense, Low-field NMR is the branch of NMR that is not conducted in superconducting high-field magnets. Low field NMR also includes Earth's field NMR where simply the Earth's magnetic field is exploited to cause nuclear spin-precession which is detected. With magnetic fields on the order of μT and below magnetometers such as SQUIDs or atomic magnetometers are used as detectors. "Normal" high field NMR relies on the detection of spin-precession with inductive detection with a simple coil. However, this detection modality becomes less sensitive as the magnetic field and the associated frequencies decrease. Hence the push toward alternative detection methods at very low fields.
The squid giant synapse is a chemical synapse found in squid. It is the largest known chemical junction in nature.
Magnetic Field Imaging (MFI) is a non-invasive and side-effect-free cardiac diagnostic method. In more recent technology, magnetocardiography (MCG) has become the clinically predominant application for recording the heart's magnetic signals. that detects and records the electromagnetic signals that are associated with the heartbeat using a multi-channel magnetic sensor array. The electric signals are known from the ECG. In the 1990s and beyond, more recent technology has supplanted the MFI, particularly MCG (xref. Cardiomag Imaging, Inc.). Through clinical research in Europe, Asia, and the U.S. (see publications in footnotes), MCG has been proven to have practical application for diagnosis of cardiac disease, and has become the clinically predominant application for recording the heart's magnetic signals. In comparison to MCG, MFI, among others, records the whole relevant area above the chest of the person.
In neurophysiology, several mathematical models of the action potential have been developed, which fall into two basic types. The first type seeks to model the experimental data quantitatively, i.e., to reproduce the measurements of current and voltage exactly. The renowned Hodgkin–Huxley model of the axon from the Loligo squid exemplifies such models. Although qualitatively correct, the H-H model does not describe every type of excitable membrane accurately, since it considers only two ions, each with only one type of voltage-sensitive channel. However, other ions such as calcium may be important and there is a great diversity of channels for all ions. As an example, the cardiac action potential illustrates how differently shaped action potentials can be generated on membranes with voltage-sensitive calcium channels and different types of sodium/potassium channels. The second type of mathematical model is a simplification of the first type; the goal is not to reproduce the experimental data, but to understand qualitatively the role of action potentials in neural circuits. For such a purpose, detailed physiological models may be unnecessarily complicated and may obscure the "forest for the trees". The FitzHugh–Nagumo model is typical of this class, which is often studied for its entrainment behavior. Entrainment is commonly observed in nature, for example in the synchronized lighting of fireflies, which is coordinated by a burst of action potentials; entrainment can also be observed in individual neurons. Both types of models may be used to understand the behavior of small biological neural networks, such as the central pattern generators responsible for some automatic reflex actions. Such networks can generate a complex temporal pattern of action potentials that is used to coordinate muscular contractions, such as those involved in breathing or fast swimming to escape a predator.
The bidomain model is a mathematical model to define the electrical activity of the heart. It consists in a continuum (volume-average) approach in which the cardiac microstructure is defined in terms of muscle fibers grouped in sheets, creating a complex three-dimensional structure with anisotropical properties. Then, to define the electrical activity, two interpenetrating domains are considered, which are the intracellular and extracellular domains, representing respectively the space inside the cells and the region between them.
Quatrefoil reentry is a type of cardiac arrhythmia that consists of two adjacent figure-of-eight reentrant circuits.
Robert Plonsey was the Pfizer-Pratt University Professor Emeritus of Biomedical Engineering at Duke University. He is noted for his work on bioelectricity.
Magnetomyography (MMG) is a technique for mapping muscle activity by recording magnetic fields produced by electrical currents occurring naturally in the muscles, using arrays of SQUIDs. It has a better capability than electromyography for detecting slow or direct currents. The magnitude of the MMG signal is in the scale of pico (10−12) to femto (10−15) Tesla (T). Miniaturizing MMG offers a prospect to modernize the bulky SQUID to wearable miniaturized magnetic sensors.
Bioelectrodynamics is a branch of medical physics and bioelectromagnetism which deals with rapidly changing electric and magnetic fields in biological systems, i.e. high frequency endogenous electromagnetic phenomena in living cells. Unlike the events studied by the electrophysiology, the generating mechanism of bioelectrodynamic phenomenon is not connected with currents of ions and its frequency is typically much higher. Examples include vibrations of electrically polar intracellular structures and non-thermal emission of photons as a result of metabolic activity.
A peripheral nerve interface is the bridge between the peripheral nervous system and a computer interface which serves as a bi‐directional information transducer recording and sending signals between the human body and a machine processor. Interfaces to the nervous system usually take the form of electrodes for stimulation and recording, though chemical stimulation and sensing are possible. Research in this area is focused on developing peripheral nerve interfaces for the restoration of function following disease or injury to minimize associated losses. Peripheral nerve interfaces also enable electrical stimulation and recording of the peripheral nervous system to study the form and function of the peripheral nervous system. For example, recent animal studies have demonstrated high accuracy in tracking physiological meaningful measures, like joint angle. Many researchers also focus in the area of neuroprosthesis, linking the human nervous system to bionics in order to mimic natural sensorimotor control and function. Successful implantation of peripheral nerve interfaces depend on a number of factors which include appropriate indication, perioperative testing, differentiated planning, and functional training. Typically microelectrode devices are implanted adjacent to, around or within the nerve trunk to establish contact with the peripheral nervous system. Different approaches may be used depending on the type of signal desired and attainable.
John Harris Miller Jr. is an American physicist with important contributions to the fields of physics, biophysics, Impedance spectroscopy, and material science, mainly known for his role in Charge density wave, research work on Cuprates and Impedance spectroscopy of living organisms. He is particularly known for an effect "Collective Quantum Tunneling of CDW Electrons" and for a well-known paper on the topic written by him and his colleagues, as published in Physical Review Letters. He was a noteworthy student of the twice Nobel laureate physicist John Bardeen who mentioned him at several places in his biography "True Genius: The Life and Science of John Bardeen".
John Walter Woodbury (1923–2017) was an American electrophysiologist and author of the first textbook explanation of the Hodgkin-Huxley_model studies of the action potential. He applied physical and mathematical techniques to experimentally elucidate the nature of electrical excitability in cells. He was also involved in the experimental and theoretical investigations of the mechanisms of ion penetration through the ion channels in muscle membranes, the regulation of cellular acid-base balance and the control of epileptic seizures by repetitive Vagus nerve stimulation.
Donald Choy Chang is a founding professor of the Hong Kong University of Science and Technology (HKUST). He was also the founding President of the Biophysical Society of Hong Kong. He is currently Professor Emeritus and Adjunct Professor in HKUST. Chang has wide research interests. He was an experimental physicist by training; but his publication ranges from nuclear magnetic resonance, biophysics and quantum physics. He was elected American Physical Society Fellow in 2023.
Brian M. Salzberg is an American neuroscientist, biophysicist and professor. He is Professor of Neuroscience and of Physiology at the Perelman School of Medicine, University of Pennsylvania.
William Archer Hagins was an American medical researcher. He was chief of the Section of Membrane Biophysics in National Institute of Diabetes and Digestive and Kidney Diseases's Laboratory of Chemical Physics upon his retirement in 2007. Hagins and colleagues made the seminal discovery of the dark current in photoreceptor cells. This finding became central to understanding how the visual cells worked and led to knowledge of the importance of reattaching a detached retina as soon as possible for continued use. As a fellow of Fulbright Program, he'd also served in the United States Navy as a Research Medical Officer. He joined NIDDK's Laboratory of Physical Biology in 1958, doing independent research in the Section of Photobiology, headed by Frederick Sumner Brackett. Hagins was a mentor to many, particularly through his work with the Brackett Foundation.
