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Voltage Clamp
The voltage clamp is an experimental method used by electrophysiologists to measure the ion currents through the membranes of excitable cells, such as neurons, while holding the membrane voltage at a set level. A basic voltage clamp will iteratively measure the membrane potential, and then change the membrane potential (voltage) to a desired value by adding the necessary current. This "clamps" the cell membrane at a desired constant voltage, allowing the voltage clamp to record what currents are delivered. Because the currents applied to the cell must be equal to (and opposite in charge to) the current going across the cell membrane at the set voltage, the recorded currents indicate how the cell reacts to changes in membrane potential. Cell membranes of excitable cells contain many different kinds of ion channels, some of which are voltage-gated. The voltage clamp allows the membrane voltage to be manipulated independently of the ionic currents, allowing the current–voltag ...
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Voltage Clamp Setup
Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to move a positive test charge from the first point to the second point. In the International System of Units (SI), the derived unit for voltage is the ''volt'' (''V''). The voltage between points can be caused by the build-up of electric charge (e.g., a capacitor), and from an electromotive force (e.g., electromagnetic induction in a generator). On a macroscopic scale, a potential difference can be caused by electrochemical processes (e.g., cells and batteries), the pressure-induced piezoelectric effect, and the thermoelectric effect. Since it is the difference in electric potential, it is a physical scalar quantity. A voltmeter can be used to measure the voltage between two points in a system. Often a common reference potential such as t ...
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Electrical Insulation
Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwell's equations. Common phenomena are related to electricity, including lightning, static electricity, electric heating, electric discharges and many others. The presence of either a positive or negative electric charge produces an electric field. The motion of electric charges is an electric current and produces a magnetic field. In most applications, Coulomb's law determines the force acting on an electric charge. Electric potential is the work done to move an electric charge from one point to another within an electric field, typically measured in volts. Electricity plays a central role in many modern technologies, serving in electric power where electric current is used to energise equipment, and in electronics dealing wi ...
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Operational Amplifier
An operational amplifier (often op amp or opamp) is a direct coupling, DC-coupled Electronic component, electronic voltage amplifier with a differential input, a (usually) Single-ended signaling, single-ended output, and an extremely high gain (electronics), gain. Its name comes from its original use of performing mathematical operations in analog computers. By using negative feedback, an Op amp circuits, op amp circuit's characteristics (e.g. its gain, input and output impedance, bandwidth (signal processing), bandwidth, and functionality) can be determined by external components and have little dependence on temperature coefficients or engineering tolerance in the op amp itself. This flexibility has made the op amp a popular building block in analog circuits. Today, op amps are used widely in consumer, industrial, and scientific electronics. Many standard integrated circuit op amps cost only a few cents; however, some integrated or hybrid operational amplifiers with special p ...
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Feedback Amplifier
A negative-feedback amplifier (or feedback amplifier) is an electronic amplifier that subtracts a fraction of its output from its input, so that negative feedback opposes the original signal. The applied negative feedback can improve its performance (gain stability, linearity, frequency response, step response) and reduces sensitivity to parameter variations due to manufacturing or environment. Because of these advantages, many amplifiers and control systems use negative feedback. An idealized negative-feedback amplifier as shown in the diagram is a system of three elements (see Figure 1): * an ''amplifier'' with gain ''A''OL, * a ''feedback network'' ''β'', which senses the output signal and possibly transforms it in some way (for example by attenuating or filtering it), * a summing circuit that acts as a ''subtractor'' (the circle in the figure), which combines the input and the transformed output. Overview Fundamentally, all electronic devices that provide power gai ...
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Electrical Ground
In electrical engineering, ground or earth may be a reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the Earth. Electrical circuits may be connected to ground for several reasons. Exposed conductive parts of electrical equipment are connected to ground to protect users from electrical shock hazards. If internal insulation fails, dangerous voltages may appear on the exposed conductive parts. Connecting exposed conductive parts to a "ground" wire which provides a low-impedance path for current to flow back to the incoming neutral (which is also connected to ground, close to the point of entry) will allow circuit breakers (or RCDs) to interrupt power supply in the event of a fault. In electric power distribution systems, a protective earth (PE) conductor is an essential part of the safety provided by the earthing system. Connection to ground also limits the build-up of static el ...
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Transmembrane Voltage
Membrane potential (also transmembrane potential or membrane voltage) is the difference in electric potential between the interior and the exterior of a biological cell. It equals the interior potential minus the exterior potential. This is the energy (i.e. work) per charge which is required to move a (very small) positive charge at constant velocity across the cell membrane from the exterior to the interior. (If the charge is allowed to change velocity, the change of kinetic energy and production of radiation must be taken into account.) Typical values of membrane potential, normally given in units of milli volts and denoted as mV, range from −80 mV to −40 mV. For such typical negative membrane potentials, positive work is required to move a positive charge from the interior to the exterior. However, thermal kinetic energy allows ions to overcome the potential difference. For a selectively permeable membrane, this permits a net flow against the gradient. This is a kind o ...
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Nobel Prize In Physiology Or Medicine
The Nobel Prize in Physiology or Medicine () is awarded yearly by the Nobel Assembly at the Karolinska Institute for outstanding discoveries in physiology or medicine. The Nobel Prize is not a single prize, but five separate prizes that, according to Alfred Nobel's 1895 will, are awarded "to those who, during the preceding year, have conferred the greatest benefit to humankind". Nobel Prizes are awarded in the fields of Physics, Medicine or Physiology, Chemistry, Literature, and Peace. The Nobel Prize is presented annually on the anniversary of Alfred Nobel's death, 10 December. As of 2024, 115 Nobel Prizes in Physiology or Medicine have been awarded to 229 laureates, 216 men and 13 women. The first one was awarded in 1901 to the German physiologist, Emil von Behring, for his work on serum therapy and the development of a vaccine against diphtheria. The first woman to receive the Nobel Prize in Physiology or Medicine, Gerty Cori, received it in 1947 for her role in elucida ...
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Hodgkin–Huxley Model
The Hodgkin–Huxley model, or conductance-based model, is a mathematical model that describes how action potentials in neurons are initiated and propagated. It is a set of nonlinear differential equations that approximates the electrical engineering characteristics of excitable cells such as neurons and muscle cells. It is a continuous-time dynamical system. Alan Hodgkin and Andrew Huxley described the model in 1952 to explain the ionic mechanisms underlying the initiation and propagation of action potentials in the squid giant axon. They received the 1963 Nobel Prize in Physiology or Medicine for this work. Basic components The typical Hodgkin–Huxley model treats each component of an excitable cell as an electrical element (as shown in the figure). The lipid bilayer is represented as a capacitance (Cm). Voltage-gated ion channels are represented by electrical conductances (''g''''n'', where ''n'' is the specific ion channel) that depend on both voltage and time. Leak chann ...
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Action Potential
An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific Cell (biology), cell rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of Membrane potential#Cell excitability, excitable cells, which include animal cells like neurons and myocyte, muscle cells, as well as some plant cells. Certain endocrine cells such as pancreatic beta cells, and certain cells of the anterior pituitary gland are also excitable cells. In neurons, action potentials play a central role in cell–cell interaction, cell–cell communication by providing for—or with regard to saltatory conduction, assisting—the propagation of signals along the neuron's axon toward axon terminal, synaptic boutons situated at the ends of an axon; these signals can then connect wit ...
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Andrew Huxley
Sir Andrew Fielding Huxley (22 November 191730 May 2012) was an English physiologist and biophysicist. He was born into the prominent Huxley family. After leaving Westminster School in central London, he went to Trinity College, Cambridge, on a scholarship, after which he joined Alan Hodgkin to study nerve impulses. Their eventual discovery of the basis for propagation of nerve impulses (called an action potential) earned them the Nobel Prize in Physiology or Medicine in 1963. They made their discovery from the giant axon of the Atlantic squid. Soon after the outbreak of the Second World War, Huxley was recruited by the British Anti-Aircraft Command and later transferred to the Admiralty. After the war he resumed research at the University of Cambridge, where he developed interference microscopy that would be suitable for studying muscle fibres. In 1952, he was joined by a German physiologist Rolf Niedergerke. Together they discovered in 1954 the mechanism of muscle co ...
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Alan Lloyd Hodgkin
Sir Alan Lloyd Hodgkin (5 February 1914 – 20 December 1998) was an English physiologist and biophysicist who shared the 1963 Nobel Prize in Physiology or Medicine with Andrew Huxley and John Eccles. Early life and education Hodgkin was born in Banbury, Oxfordshire, on 5 February 1914. He was the oldest of three sons of Quakers George Hodgkin and Mary Wilson Hodgkin. His father was the son of Thomas Hodgkin and had read for the Natural Science Tripos at Cambridge where he had befriended electrophysiologist Keith Lucas. Because of poor eyesight, he was unable to study medicine and eventually ended up working for a bank in Banbury. As members of the Society of Friends, George and Mary opposed the Military Service Act of 1916, which introduced conscription, and had to endure a great deal of abuse from their local community, including an attempt to throw George in one of the town canals. In 1916, George Hodgkin travelled to Armenia as part of an investigation of distress. ...
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Squid Giant Axon
The squid giant axon is the very large (up to 1.5 mm in diameter; typically around 0.5 mm) axon that controls part of the water jet propulsion system in squid. It was first described by L. W. Williams in 1909, but this discovery was forgotten until English zoologist and neurophysiologist J. Z. Young demonstrated the axon's function in the 1930s while working in the Stazione Zoologica in Naples, the Marine Biological Association in Plymouth and the Marine Biological Laboratory in Woods Hole. Squids use this system primarily for making brief but very fast movements through the water. On the underside of the squid's body, between the head and the mantle, is a siphon through which water can be rapidly expelled by the fast contractions of the body wall muscles of the animal. This contraction is initiated by action potentials in the giant axon. Action potentials travel faster in an axon with a large diameter than a smaller one, and squid have evolved the giant axon ...
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