A dendrite or dendron is a branched protoplasmic extension of a nerve cell that propagates the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project. Electrical stimulation is transmitted onto dendrites by upstream neurons via synapses which are located at various points throughout the dendritic tree.
Einsteinium is a synthetic chemical element; it has symbol Es and atomic number 99. It was named in honor of Albert Einstein and is a member of the actinide series and is the seventh transuranium element.
Fermium is a synthetic chemical element; it has symbol Fm and atomic number 100. It is an actinide and the heaviest element that can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities, although pure fermium metal has not yet been prepared. A total of 20 isotopes are known, with 257Fm being the longest-lived with a half-life of 100.5 days.
Morphogenesis is the biological process that causes a cell, tissue or organism to develop its shape. It is one of three fundamental aspects of developmental biology along with the control of tissue growth and patterning of cellular differentiation.
A synthetic element is one of 24 known chemical elements that do not occur naturally on Earth: they have been created by human manipulation of fundamental particles in a nuclear reactor, a particle accelerator, or the explosion of an atomic bomb; thus, they are called "synthetic", "artificial", or "man-made". The synthetic elements are those with atomic numbers 95–118, as shown in purple on the accompanying periodic table: these 24 elements were first created between 1944 and 2010. The mechanism for the creation of a synthetic element is to force additional protons into the nucleus of an element with an atomic number lower than 95. All known synthetic elements are unstable, but they decay at widely varying rates: the half-lives of their longest-lived isotopes range from microseconds to millions of years.
Sir Andrew Fielding Huxley 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 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.
An action potential occurs when the membrane potential of a specific cell rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of excitable cells, which include animal cells like neurons and 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.
Haemophilia B, also spelled hemophilia B, is a blood clotting disorder causing easy bruising and bleeding due to an inherited mutation of the gene for factor IX, and resulting in a deficiency of factor IX. It is less common than factor VIII deficiency.
Sir Alan Lloyd Hodgkin was an English physiologist and biophysicist who shared the 1963 Nobel Prize in Physiology or Medicine with Andrew Huxley and John Eccles.
The year 1949 in science and technology involved some significant events, listed below.
Eric Francis Wieschaus is an American evolutionary developmental biologist and 1995 Nobel Prize-winner.
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.
The squid giant axon is the very large 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.
The soliton hypothesis in neuroscience is a model that claims to explain how action potentials are initiated and conducted along axons based on a thermodynamic theory of nerve pulse propagation. It proposes that the signals travel along the cell's membrane in the form of certain kinds of solitary sound pulses that can be modeled as solitons. The model is proposed as an alternative to the Hodgkin–Huxley model in which action potentials: voltage-gated ion channels in the membrane open and allow sodium ions to enter the cell. The resulting decrease in membrane potential opens nearby voltage-gated sodium channels, thus propagating the action potential. The transmembrane potential is restored by delayed opening of potassium channels. Soliton hypothesis proponents assert that energy is mainly conserved during propagation except dissipation losses; Measured temperature changes are completely inconsistent with the Hodgkin-Huxley model.
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 Department of Physiology, Development and Neuroscience, (PDN) is a part of the School of Biological Sciences at the University of Cambridge. Research in PDN focuses on three main areas: Cellular and Systems Physiology, Developmental and Reproductive Biology, and Neuroscience and is currently headed by Sarah Bray and William Colledge. The department was formed on 1 January 2006, within the School of Biological Sciences at the University of Cambridge from the merger of the Departments of Anatomy and Physiology. The department hosts the Centre for Trophoblast Research and has links with the Cambridge Centre for Brain Repair, the Cambridge Stem Cell Institute, and the Gurdon Institute.
Neural accommodation or neuronal accommodation occurs when a neuron or muscle cell is depolarised by slowly rising current in vitro. The Hodgkin–Huxley model also shows accommodation. Sudden depolarisation of a nerve evokes propagated action potential by activating voltage-gated fast sodium channels incorporated in the cell membrane if the depolarisation is strong enough to reach threshold. The open sodium channels allow more sodium ions to flow into the cell and resulting in further depolarisation, which will subsequently open even more sodium channels. At a certain moment this process becomes regenerative and results in the rapid ascending phase of action potential. In parallel with the depolarisation and sodium channel activation, the inactivation process of the sodium channels is also driven by depolarisation. Since the inactivation is much slower than the activation process, during the regenerative phase of action potential, inactivation is unable to prevent the "chain reaction"-like rapid increase in the membrane voltage.
Gilbert Ning Ling was a Chinese-born American cell physiologist, biochemist and scientific investigator.
The sliding filament theory explains the mechanism of muscle contraction based on muscle proteins that slide past each other to generate movement. According to the sliding filament theory, the myosin of muscle fibers slide past the actin during muscle contraction, while the two groups of filaments remain at relatively constant length.
The Hodgkin family is a British Quaker family where several members have excelled in science, medicine, and arts.