They focused on a part of the eye called the retinal nerve-fibre layer (RNFL).
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The nerve fibre is a thread-like extension of a nerve cell that includes the axon which may or may not be encased in a myelinated sheath. The androgenic nerve fibre when myelinated increases the speed of transmission for an action potential across the length of the cell. The gaps in the sheath along the axon are call the node of ranvier.
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There are two types of nerve fibre relevant to pain in fish. Group C nerve fibres are a type of sensory nerve fibre which lack a myelin sheath and have a small diameter, meaning they have a low nerve conduction velocity. The suffering that humans associate with burns, toothaches, or crushing injury are caused by C fibre activity. A typical human cutaneous nerve contains 83% Group C nerve fibres.
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Early electrophysiological studies in frogs report that noxious mechanical, thermal and chemical stimuli excite primary afferent fibres with slowly conducting axons. There are two types of nerve fibre relevant to pain in amphibians. Group C nerve fibres are a type of sensory nerve fibre which lack a myelin sheath and have a small diameter, meaning they have a low nerve conduction velocity. The suffering associated with burns, toothaches, or crushing injury are caused by C fibre activity.
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For example, a cortical efferent is a fibre coming from elsewhere, and arriving to the cortex. Note that that is the opposite of the direction in which the nerve fibre conducts signals.
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Also, she discovered that when two nerve fibres are close in proximity, the activity of a single nerve fibre can generate activity in a nearby nerve fibre. Arvanitaki and her husband Chalazonitis both explored the methodology of electrophysiological activity of the nervous system of the sea hare genus Aplysia. In 1955, Arvanitaki and Chalazonitis as well as Ladislav Tauc created the first intracellular recordings of large neurons of the California sea hare. Arvanitaki's and Chalazonitis' explored photoexcitability of certain neurons.
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Art and Medicine Die Photographie als Hülfsmittel mikroskopischer Forschung Along with Camillo Golgi, he was a major proponent of the reticular theory that the brain's nervous system consisted of processes of contiguous cells fused to create a massive meshed network. Gerlach summed up his theory by stating: > the finest divisions of the protoplasmic processes ultimately take part in > the formation of the fine nerve fibre network which I consider to be an > essential constituent of the gray matter of the spinal cord. The divisions > are none other than the beginnings of this nerve fibre net. The cells of the > gray matter are therefore doubly connected by means the nerve process which > becomes the axis fibre and through the finest branches of the protoplasmic > processes which become a part of the fine nerve fibre net of the gray > matter.
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Information in each nerve fibre is represented by the rate of action potentials as well as the particular timing of individual action potentials. The particular physiology and morphology of each cochlear nucleus cell type enhances different aspects of sound information.
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The inner mesaxon (Terminologia histologica: Mesaxon internum) is the connection between the myelin sheath and the inner part of the cell membrane of the Schwann cell which is directly opposite the axolemma, i.e. the cell membrane of the nerve fibre ensheathed by the Schwann cell.
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Phoronis ovalis is a small horseshoe worm growing to an extended length of and a diameter of . It exhibits many primitive traits. The lophophore is simple and oval in shape, with 11 to 28 tentacles. The giant nerve fibre typical of the genus is not present.
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The gonads are located in the metacoel. There are two blood vessels running along the ventral and dorsal sides of the body with capillaries in the tentacles. These are made easily visible by the haemoglobin in the red blood cells. There is a single nerve fibre on the left side of the body.
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A-delta fibres are another type of sensory nerve fibre, however, these are myelinated and therefore transmit impulses faster than non-myelinated C fibres. A-delta fibres carry cold, pressure and some pain signals, and are associated with acute pain that results in "pulling away" from noxious stimuli. The skin of frogs contains both Group C fibres and A-delta fibres.
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As long as the stimulus reaches the threshold, the full response would be given. Larger stimulus does not result in a larger response, vice versa. The magnitude of the action potential set up in any single nerve fibre is independent of the strength of the exciting stimulus, provided the latter is adequate. An electrical stimulus below threshold strength fails to elicit a propagated spike potential.
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Furthermore, scanning laser polarimetry utilises the birefringence of the optic nerve fibre layer to indirectly quantify its thickness, which is of use in the assessment and monitoring of glaucoma. Birefringence characteristics in sperm heads allow the selection of spermatozoa for intracytoplasmic sperm injection. Likewise, zona imaging uses birefringence on oocytes to select the ones with highest chances of successful pregnancy. Birefringence of particles biopsied from pulmonary nodules indicates silicosis.
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His team investigated the biochemical conditions which control nerve fibre growth and also sought ways to accelerate the repair of peripheral nerves severed by injury. Working with Peter Medawar, Young found a way to rejoin small peripheral nerves using a "glue" of plasma. This method was eventually modified and used in surgery. After WWII, Young's research interests turned to investigating the central nervous system and the functions of the brain.
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NEC are also found in all four gill arches within several different structures, such as along the filaments, at the ends of the gill rakers and throughout the lamellae. Two separate neural pathways have been identified within the zebrafish gill arches both the motor and sensory nerve fibre pathways. Since neuroepithelial cells are distributed throughout the gills, they are often ideally situated to detect both arterial as well as environmental oxygen.
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Muscarinic antagonists can bind to muscarinic receptors and block the receptors. Acetylcholine cannot interact with muscarinic receptors so transmission of nerve impulses cannot be passed from neurons to organs to bring about the original physiological response. For inhibitors of acetylcholine release, they can impede the release of acetylcholine from the presynaptic nerve fibre. In this way, there is a decline in neurotransmission and the corresponding physiological effect will be diminished.
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Stimuli too weak to produce a spike do, however, set up a local electrotonus, the magnitude of the electronic potential progressively increasing with the strength of the stimulus, until a spike is generated. This demonstrates the all-or-none relationship in spike production. The above account deals with the response of a single nerve fibre. If a nerve trunk is stimulated, then as the exciting stimulus is progressively increased above a threshold, a larger number of fibres respond.
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The retinal nerve fibre layer should also be studied and commented on. It is also a useful tool in objectively measuring torsion as well as in documenting and recording progression of diseases over time. Fundus photography does not replace binocular indirect ophthalmoscopy; it is a tool to supplement and complement existing findings and to maintain a record of disease progression. Fundus photography is mainly used to monitor the progression of a retinal or optic nerve head disorder.
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The exact position of the electrode tip within the nerve is then adjusted in minute steps until the electrode discriminates impulses of the neural system of interest. A unique feature and a significant strength of the microneurography method is that subjects are fully awake and able to cooperate in tests requiring mental attention, while impulses in a representative nerve fibre or set of nerve fibres are recorded, e.g. when cutaneous sense organs are stimulated or subjects perform voluntary precision movements.
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Nerve fiber innervation is much denser for inner hair cells than for outer hair cells. A single inner hair cell is innervated by numerous nerve fibers, whereas a single nerve fiber innervates many outer hair cells. Inner hair cell nerve fibers are also very heavily myelinated, which is in contrast to the unmyelinated outer hair cell nerve fibers. The region of the basilar membrane supplying the inputs to a particular afferent nerve fibre can be considered to be its receptive field.
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In 1849, while at Königsberg, Helmholtz measured the speed at which the signal is carried along a nerve fibre. At that time most people believed that nerve signals passed along nerves immeasurably fast. He used a recently dissected sciatic nerve of a frog and the calf muscle to which it attached. He used a galvanometer as a sensitive timing device, attaching a mirror to the needle to reflect a light beam across the room to a scale which gave much greater sensitivity.
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It has been shown that odontoblasts secrete the extracellular matrix protein reelin. A pulpal A-delta (noxious, short sharp pain) nerve fibre is either wrapped around the base of this process, or travels a short way into the dentinal tubule with the odontoblast process (max ~0.1 mm) This process lies in the dentinal tubule. In an erupted tooth, this process rarely extends beyond 1/3 the depth of the dentin, which is why the odontoblast transduction theory of dentinal hypersensivity is unlikely.
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The rate of information processing in biological neural systems are constrained by the speed at which an action potential can propagate down a nerve fibre. This conduction velocity ranges from 1 m/s to over 100 m/s, and generally increases with the diameter of the neuronal process. Slow in the timescales of biologically-relevant events dictated by the speed of sound or the force of gravity, the nervous system overwhelmingly prefers parallel computations over serial ones in time-critical applications.
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Virginia–Maryland Regional College of Veterinary Medicine From closest to farthest from the vitreous body: # Inner limiting membrane – basement membrane elaborated by Müller cells. # Nerve fibre layer – axons of the ganglion cell bodies (note that a thin layer of Müller cell footplates exists between this layer and the inner limiting membrane). # Ganglion cell layer – contains nuclei of ganglion cells, the axons of which become the optic nerve fibres, and some displaced amacrine cells. # Inner plexiform layer – contains the synapse between the bipolar cell axons and the dendrites of the ganglion and amacrine cells.
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Alan Lloyd Hodgkin spent a year (1937–38) at the Rockefeller Institute, during which he joined Cole to measure the D.C. resistance of the membrane of the squid giant axon in the resting state. In 1939 they began using internal electrodes inside the giant nerve fibre of the squid and Cole developed the voltage clamp technique in 1947. Hodgkin and Andrew Huxley later presented a mathematical model for transmission of electrical signals in neurons of the giant axon of a squid and how they are initiated and propagated, known as the Hodgkin–Huxley model.
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Indeed, JZ Young, Professor of Anatomy, 1945–74, discovered and was the first to investigate the squid giant axon. Young's work on squid giant axons was utilized by Andrew Huxley and Alan Hodgkin who in 1963 received the Nobel Prize for their work on the conduction of action potentials along nerve fibres. To achieve this, they developed a voltage-clamp technique to demonstrate that impulse transmission relied upon the selective permeability of the nerve fibre membrane to particular ions. This ground- breaking advance laid the foundations for much of modern-day electrophysiology.
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Hartline joined the staff of Rockefeller University, New York City, in 1953 as professor of neurophysiology. Hartline investigated the electrical responses of the retinas of certain arthropods, vertebrates, and mollusks, because their visual systems are much simpler than those of humans and thus easier to study. He concentrated his studies on the eye of the horseshoe crab (Limulus polyphemus). Using minute electrodes, he obtained the first record of the electrical impulses sent by a single optic nerve fibre when the receptors connected to it are stimulated by light.
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After his return to Cambridge he started collaborating with Andrew Huxley who had entered Trinity as a freshman in 1935, three years after Hodgkin. With a £300 equipment grant from the Rockefeller Foundation, Hodgkin managed to set up a similar physiology setup to the one he had worked with at the Rockefeller Institute. He moved all his equipment to the Plymouth Marine Laboratory in July 1939. There, he and Huxley managed to insert a fine cannula into the giant axon of squids and record action potentials from inside the nerve fibre.
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If it is of threshold strength or over, a spike (a nervous impulse) of maximum magnitude is set up. Either the single fibre does not respond with spike production, or it responds to the utmost of its ability under the conditions at the moment. This property of the single nerve fibre is termed the all-or-none relationship. This relationship holds only for the unit of tissue; for nervous tissue the unit is the nerve cell, for skeletal muscle the unit is the individual muscle fiber and for the heart the unit is the entire auricles or the entire ventricles.
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An adrenergic nerve fibre is a neuron for which the neurotransmitter is either adrenaline (epinephrine), noradrenaline or dopamine. These neurotransmitters are released at a location known as the synapse, which is a junction point between the axon of one nerve cell and the dendrite of another. The neurotransmitters are first released from the axon and then bind to the receptor site on the dendrite. Adrenergic nerve terminals are found in the secondary neurons of the sympathetic nervous system, one of two deviations of the autonomic nervous system which is responsible for the fight-or-flight response.
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A-delta fibres are another type of sensory nerve fibre, however, these are myelinated and therefore transmit impulses faster than non-myelinated C fibres. A-delta fibres carry cold, pressure and some pain signals, and are associated with acute pain that results in "pulling away" from noxious stimuli. Bony fish possess both Group C and A-delta fibres representing 38.7% (combined) of the fibres in the tail nerves of common carp and 36% of the trigeminal nerve of rainbow trout. However, only 5% and 4% of these are C fibres in the carp and rainbow trout, respectively.
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The experiments were still extremely challenging as the nerve impulses only last a fraction of a millisecond, during which time they needed to measure the changing electrical potential at different points along the nerve. Using equipment largely of their own construction and design, including one of the earliest applications of a technique of electrophysiology known as the voltage clamp, they were able to record ionic currents. In 1939, they jointly published a short paper in Nature reporting on the work done in Plymouth and announcing their achievement of recording action potentials from inside a nerve fibre. Then World War II broke out, and their research was abandoned.
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The ear filters incoming sound into different frequencies: a given place in the cochlea, and a given auditory nerve fibre, respond only to a limited range of frequencies. Consequently, researchers have examined the cues that are generated by mixtures of speech and noise at the two ears within a narrow frequency band around the signal. When a signal and narrowband noise are added, a vector summation occurs in which the resultant amplitude and phase differ from those of the noise or signal alone. For a binaural unmasking stimulus, the differences between the interaural parameters of the signal and noise mean that there will be a different vector summation at each ear.
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An axon (from Greek ἄξων áxōn, axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action potentials away from the nerve cell body. The function of the axon is to transmit information to different neurons, muscles, and glands. In certain sensory neurons (pseudounipolar neurons), such as those for touch and warmth, the axons are called afferent nerve fibers and the electrical impulse travels along these from the periphery to the cell body, and from the cell body to the spinal cord along another branch of the same axon. Axon dysfunction has caused many inherited and acquired neurological disorders which can affect both the peripheral and central neurons.
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There he met Rafael Lorente de Nó and Kenneth Stewart Cole with whom he ended up publishing a paper. During that year he also spent time at the Woods Hole Marine Biological Laboratory where he was introduced to the squid giant axon, which ended up being the model system with which he conducted most of the research that eventually led to his Nobel Prize. In spring 1938 he visited Joseph Erlanger at Washington University in St. Louis who told him he would take Hodgkin's local circuit theory of nerve impulse propagation seriously if he could show that altering the resistance of the fluid outside a nerve fibre made a difference to the velocity of nerve impulse conduction. Working with single nerve fibres from shore crabs and squids, he showed that the conduction rate was much faster in sea water than in oil, providing strong evidence for the local circuit theory.
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