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An axon or nerve fiber 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,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 can be the cause of many inherited and acquired neurological disorders that affect both the peripheral and central neurons. Nerve fibers are classed into three types –group A nerve fibers,group B nerve fibers,and group C nerve fibers. Groups A and B are myelinated,and group C are unmyelinated. These groups include both sensory fibers and motor fibers. Another classification groups only the sensory fibers as Type I,Type II,Type III,and Type IV.
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.
Myelin is a lipid-rich material that surrounds nerve cell axons to insulate them and increase the rate at which electrical impulses pass along the axon. The myelinated axon can be likened to an electrical wire with insulating material (myelin) around it. However,unlike the plastic covering on an electrical wire,myelin does not form a single long sheath over the entire length of the axon. Rather,myelin ensheaths the axon segmentally:in general,each axon is encased in multiple long sheaths with short gaps between,called nodes of Ranvier. At the nodes of Ranvier,which are approximately one thousandth of a mm in length,the axon's membrane is bare of myelin.
A neuron,neurone,or nerve cell is an excitable cell that fires electric signals called action potentials across a neural network in the nervous system. Neurons communicate with other cells via synapses,which are specialized connections that commonly use minute amounts of chemical neurotransmitters to pass the electric signal from the presynaptic neuron to the target cell through the synaptic gap.
Chemical synapses are biological junctions through which neurons' signals can be sent to each other and to non-neuronal cells such as those in muscles or glands. Chemical synapses allow neurons to form circuits within the central nervous system. They are crucial to the biological computations that underlie perception and thought. They allow the nervous system to connect to and control other systems of the body.
Electrophysiology is the branch of physiology that studies the electrical properties of biological cells and tissues. It involves measurements of voltage changes or electric current or manipulations on a wide variety of scales from single ion channel proteins to whole organs like the heart. In neuroscience,it includes measurements of the electrical activity of neurons,and,in particular,action potential activity. Recordings of large-scale electric signals from the nervous system,such as electroencephalography,may also be referred to as electrophysiological recordings. They are useful for electrodiagnosis and monitoring.
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.
In biology,depolarization or hypopolarization is a change within a cell,during which the cell undergoes a shift in electric charge distribution,resulting in less negative charge inside the cell compared to the outside. Depolarization is essential to the function of many cells,communication between cells,and the overall physiology of an organism.
The supraoptic nucleus (SON) is a nucleus of magnocellular neurosecretory cells in the hypothalamus of the mammalian brain. The nucleus is situated at the base of the brain,adjacent to the optic chiasm. In humans,the SON contains about 3,000 neurons.
Magnocellular neurosecretory cells are large neuroendocrine cells within the supraoptic nucleus and paraventricular nucleus of the hypothalamus. They are also found in smaller numbers in accessory cell groups between these two nuclei,the largest one being the circular nucleus. There are two types of magnocellular neurosecretory cells,oxytocin-producing cells and vasopressin-producing cells,but a small number can produce both hormones. These cells are neuroendocrine neurons,are electrically excitable,and generate action potentials in response to afferent stimulation. Vasopressin is produced from the vasopressin-producing cells via the AVP gene,a molecular output of circadian pathways.
End plate potentials (EPPs) are the voltages which cause depolarization of skeletal muscle fibers caused by neurotransmitters binding to the postsynaptic membrane in the neuromuscular junction. They are called "end plates" because the postsynaptic terminals of muscle fibers have a large,saucer-like appearance. When an action potential reaches the axon terminal of a motor neuron,vesicles carrying neurotransmitters are exocytosed and the contents are released into the neuromuscular junction. These neurotransmitters bind to receptors on the postsynaptic membrane and lead to its depolarization. In the absence of an action potential,acetylcholine vesicles spontaneously leak into the neuromuscular junction and cause very small depolarizations in the postsynaptic membrane. This small response (~0.4mV) is called a miniature end plate potential (MEPP) and is generated by one acetylcholine-containing vesicle. It represents the smallest possible depolarization which can be induced in a muscle.
In cellular neuroscience,the soma,perikaryon,neurocyton,or cell body is the bulbous,non-process portion of a neuron or other brain cell type,containing the cell nucleus. Although it is often used to refer to neurons,it can also refer to other cell types as well,including astrocytes,oligodendrocytes,and microglia. There are many different specialized types of neurons,and their sizes vary from as small as about 5 micrometres to over 10 millimetres for some of the smallest and largest neurons of invertebrates,respectively.
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.
Neurotransmission is the process by which signaling molecules called neurotransmitters are released by the axon terminal of a neuron,and bind to and react with the receptors on the dendrites of another neuron a short distance away. A similar process occurs in retrograde neurotransmission,where the dendrites of the postsynaptic neuron release retrograde neurotransmitters that signal through receptors that are located on the axon terminal of the presynaptic neuron,mainly at GABAergic and glutamatergic synapses.
In the nervous system,a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another neuron or to the target effector cell.
The squid giant synapse is a chemical synapse found in squid. It is the largest known chemical junction in nature.
Voltage-sensitive dyes,also known as potentiometric dyes,are dyes which change their spectral properties in response to voltage changes. They are able to provide linear measurements of firing activity of single neurons,large neuronal populations or activity of myocytes. Many physiological processes are accompanied by changes in cell membrane potential which can be detected with voltage sensitive dyes. Measurements may indicate the site of action potential origin,and measurements of action potential velocity and direction may be obtained.
In neurophysiology,a dendritic spike refers to an action potential generated in the dendrite of a neuron. Dendrites are branched extensions of a neuron. They receive electrical signals emitted from projecting neurons and transfer these signals to the cell body,or soma. Dendritic signaling has traditionally been viewed as a passive mode of electrical signaling. Unlike its axon counterpart which can generate signals through action potentials,dendrites were believed to only have the ability to propagate electrical signals by physical means:changes in conductance,length,cross sectional area,etc. However,the existence of dendritic spikes was proposed and demonstrated by W. Alden Spencer,Eric Kandel,Rodolfo Llinás and coworkers in the 1960s and a large body of evidence now makes it clear that dendrites are active neuronal structures. Dendrites contain voltage-gated ion channels giving them the ability to generate action potentials. Dendritic spikes have been recorded in numerous types of neurons in the brain and are thought to have great implications in neuronal communication,memory,and learning. They are one of the major factors in long-term potentiation.
Axon terminals are distal terminations of the branches of an axon. An axon,also called a nerve fiber,is a long,slender projection of a nerve cell that conducts electrical impulses called action potentials away from the neuron's cell body to transmit those impulses to other neurons,muscle cells,or glands. Most presynaptic terminals in the central nervous system are formed along the axons,not at their ends.
Cellular neuroscience is a branch of neuroscience concerned with the study of neurons at a cellular level. This includes morphology and physiological properties of single neurons. Several techniques such as intracellular recording,patch-clamp,and voltage-clamp technique,pharmacology,confocal imaging,molecular biology,two photon laser scanning microscopy and Ca2+ imaging have been used to study activity at the cellular level. Cellular neuroscience examines the various types of neurons,the functions of different neurons,the influence of neurons upon each other,and how neurons work together.
References
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- ↑ Salzberg, B.M., H.V. Davila, and L.B. Cohen. (1973). Optical recording of impulses in individual neurones of an invertebrate central nervous system. Nature, 246, 508-509.
- 1 2 Salzberg, Brian M. (2017). "Reminiscences of time spent with Amiram Grinvald". Neurophotonics. 4 (3): 031201. doi:10.1117/1.NPh.4.3.031201. PMC 5533194 . PMID 28785599.
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- ↑ Brown, J. E.; Cohen, L. B.; De Weer, P.; Pinto, L. H.; Ross, W. N.; Salzberg, B. M. (1975). "Rapid changes in intracellular free calcium concentration. Detection by metallochromic indicator dyes in squid giant axon". Biophysical Journal. 15 (11): 1155–60. Bibcode:1975BpJ....15.1155B. doi:10.1016/S0006-3495(75)85891-7. PMC 1334796 . PMID 1201331.
- ↑ "Large and rapid changes in light scattering accompany secretion by nerve terminals in the mammalian neurohypophysis".
- ↑ Parsons, T. D.; Kleinfeld, D.; Raccuia-Behling, F.; Salzberg, B. M. (1989). "Optical recording of the electrical activity of synaptically interacting Aplysia neurons in culture using potentiometric probes". Biophysical Journal. 56 (1): 213–221. Bibcode:1989BpJ....56..213P. doi:10.1016/S0006-3495(89)82666-9. PMC 1280466 . PMID 2752089.
- ↑ Rohr, S.; Salzberg, B. M. (1994). "Multiple site optical recording of transmembrane voltage (MSORTV) in patterned growth heart cell cultures: assessing electrical behavior, with microsecond resolution, on a cellular and subcellular scale". Biophysical Journal. 67 (3): 1301–15. Bibcode:1994BpJ....67.1301R. doi:10.1016/S0006-3495(94)80602-2. PMC 1225487 . PMID 7811945.
- ↑ Salzberg, B. M.; Davila, H. V.; Cohen, L. B. (1973). "Optical Recording of Impulses in Individual Neurones of an Invertebrate Central Nervous System". Nature. 246 (5434): 508–509. Bibcode:1973Natur.246..508S. doi:10.1038/246508a0. PMID 4357630. S2CID 3337830.
- ↑ Vergara, J.; Bezanilla, F.; Salzberg, B. M. (1978). "Nile blue fluorescence signals from cut single muscle fibers under voltage or current clamp conditions". The Journal of General Physiology. 72 (6): 775–800. doi:10.1085/jgp.72.6.775. PMC 2228492 . PMID 310445.
- ↑ Konnerth, A.; Obaid, A. L.; Salzberg, B. M. (1987). "Optical recording of electrical activity from parallel fibres and other cell types in skate cerebellar slices in vitro". The Journal of Physiology. 393: 681–702. doi:10.1113/jphysiol.1987.sp016848. PMC 1192418 . PMID 3446807.
- ↑ "Brian Salzberg-Scopus".
- ↑ "PROFILE--Brian Salzberg has finished every Falmouth Road Race (45 in a row)".
- ↑ "Aug. 11: It Takes More Than Good Legs to Run 37 Straight Falmouth Road Races". 2010-08-11.