Information about Neurobiology
Neurobiology is the study of cells of the nervous system and the organization of these cells into functional circuits that process information and mediate behavior.[1] It is a subdiscipline of both biology and neuroscience. Neurobiology differs from neuroscience, a much broader field that is concerned with any scientific study of the nervous system. Neurobiology should also not be confused with other subdisciplines of neuroscience such as computational neuroscience, cognitive neuroscience, behavioral neuroscience, biological psychiatry, neurology, and neuropsychology despite the overlap with these subdisciplines. Scientists that study neurobiology are called neurobiologists.
Neurons are cells that are specialized to receive, propagate, and transmit electrochemical impulses. In the human brain alone, there are over a hundred billion neurons. Neurons are diverse with respect to morphology and function. Thus, not all neurons correspond to the stereotypical motor neuron with dendrites and myelinated axons that conduct action potentials. Some neurons such as photoreceptors, for example, do not have myelinated axons that conduct action potentials. Other unipolar neurons found in invertebrates do not even have distinguishing processes such as dendrites. Moreover, the distinctions based on function between neurons and other cells such as cardiac and muscle cells are not helpful. Thus, the fundamental difference between a neuron and a nonneuronal cell is a matter of degree.
Another major class of cells found in the nervous system are glial cells. Despite the abundance of glial cells relative to neurons in the nervous system (there are ten glial cells for every single neuron), glial cells are only recently beginning to receive attention from neurobiologists for being involved not just in nourishment and support of neurons, but also in modulating synapses. For example, Schwann cells, a type of glial cells found in the peripheral nervous system, modulate synaptic connections between the presynaptic terminal from a motor neuron and endplate muscle fiber in the neuromuscular junction.
The Hodgkin-Huxley Model of an action potential in the squid giant axon has been the basis for much of the current understanding of the ionic bases of action potentials. Briefly, the model states that the generation of an action potential is determined by two ions: Na+ and K+. An action potential can be divided into several sequential phases: threshold, rising phase, falling phase, undershoot phase, and recovery. Following several local graded depolarizations of the membrane potential, the threshold of excitation is reached, voltage-gated sodium channels are activated, which leads to an influx of Na+ ions. As Na+ ions enter the cell, the membrane potential is further depolarized, and more voltage-gated sodium channels are activated. Such a process is also known as a positive-feedback loop. As the rising phase reaches its peak, voltage-gated Na+ channels are inactivated whereas voltage-gated K+ channels are activated, resulting in a net outward movement of K+ ions, which repolarizes the membrane potential towards the resting membrane potential. Repolarization of the membrane potential continues, resulting in an undershoot phase or absolute refractory period. The undershoot phase occurs because unlike voltage-gated sodium channels, voltage-gated potassium channels inactivate much more slowly. Nevertheless, as more voltage-gated K+ channels become inactivated, the membrane potential recovers to its normal resting steady state.
Neurons communicate with one another via synapses. Synapses are specialized junctions between two cells in close apposition to one another. In a synapse, the neuron that sends the signal is the presynaptic neuron and the target cell receives that signal is the postsynaptic neuron or cell. Synapses can be either electrical or chemical. Electrical synapses are characterized by the formation of gap junctions that allow ions and other organic compound to instantaneously pass from one cell to another.[2] Chemical synapses are characterized by the presynaptic release of neurotransmitters that diffuse across a synaptic cleft to bind with postsynaptic receptors. A neurotransmitter is a chemical messenger that is synthesized within neurons themselves and released by these same neurons to communicate with their postsynaptic target cells. A receptor is a transmembrane protein molecule that a neurotransmitter or drug binds. Chemical synapses are slower than electrical synapses.
Postsynaptic depolarizations can be either excitatory or inhibitory. Those that are excitatory are referred to as excitatory postsynaptic potential (EPSP). Alternatively, some postsynaptic receptors allow Cl- ions to enter the cell or K+ ions to leave the cell, which results in an inhibitory postsynaptic potential (IPSP). If the EPSP is dominant, the threshold of excitation in the postynaptic neuron may be reached, resulting in the generation and propagation of an action potential in the postynaptic neuron.
The auditory system is a sensory system for the sense of hearing. It consists of the outer ear, the middle ear, and the inner ear.
The olfactory system is the sensory system used for olfaction. The accessory olfactory system senses pheromones. The olfactory system is often spoken of along with the gustatory system as the chemosensory senses because both transduce chemical signals into perception. Linda B. Buck and Richard Axel won the 2004 Nobel Prize in Physiology or Medicine for their work on the olfactory system.
The visual system is the part of the nervous system which allows organisms to see. It interprets the information from visible light to build a representation of the world surrounding the body. The visual system has the complex task of (re)constructing a three dimensional world from a two dimensional projection of that world. Note that different species are able to see different parts of the light spectrum; for example, some can see into the ultraviolet, while others can see into the infrared.
Dendrites (from Greek dendron, “tree”) are the branched projections of a neuron that act to conduct the electrical stimulation received from other neural cells to the cell body, or
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Neurons and glial cells
Main articles: neuron, glial cell)
stained neuron
Neurons are cells that are specialized to receive, propagate, and transmit electrochemical impulses. In the human brain alone, there are over a hundred billion neurons. Neurons are diverse with respect to morphology and function. Thus, not all neurons correspond to the stereotypical motor neuron with dendrites and myelinated axons that conduct action potentials. Some neurons such as photoreceptors, for example, do not have myelinated axons that conduct action potentials. Other unipolar neurons found in invertebrates do not even have distinguishing processes such as dendrites. Moreover, the distinctions based on function between neurons and other cells such as cardiac and muscle cells are not helpful. Thus, the fundamental difference between a neuron and a nonneuronal cell is a matter of degree.
Another major class of cells found in the nervous system are glial cells. Despite the abundance of glial cells relative to neurons in the nervous system (there are ten glial cells for every single neuron), glial cells are only recently beginning to receive attention from neurobiologists for being involved not just in nourishment and support of neurons, but also in modulating synapses. For example, Schwann cells, a type of glial cells found in the peripheral nervous system, modulate synaptic connections between the presynaptic terminal from a motor neuron and endplate muscle fiber in the neuromuscular junction.
Neuronal function
One prominent characteristic of many neurons is excitability. Neurons generate electrical impulses or changes in voltage of two types: graded potentials and action potentials. Graded potentials occur when the membrane potential depolarizes and hyperpolarizes in a graded fashion relative to the amount of stimulus that is applied to the neuron. An action potential on the other hand is an all-or-none electrical impulse. Despite being slower than graded potentials, action potentials have the advantage of traveling long distances in axons with little or no decrement. Much of the current knowledge of action potentials comes from squid axon experiments by Sir Alan Lloyd Hodgkin and Sir Andrew Huxley.Action potential
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"Current Clamp" is a common technique in electrophysiology. This is a whole cell current clamp recording of a neuron firing a train of action potentials due to it being depolarized by current injection
The Hodgkin-Huxley Model of an action potential in the squid giant axon has been the basis for much of the current understanding of the ionic bases of action potentials. Briefly, the model states that the generation of an action potential is determined by two ions: Na+ and K+. An action potential can be divided into several sequential phases: threshold, rising phase, falling phase, undershoot phase, and recovery. Following several local graded depolarizations of the membrane potential, the threshold of excitation is reached, voltage-gated sodium channels are activated, which leads to an influx of Na+ ions. As Na+ ions enter the cell, the membrane potential is further depolarized, and more voltage-gated sodium channels are activated. Such a process is also known as a positive-feedback loop. As the rising phase reaches its peak, voltage-gated Na+ channels are inactivated whereas voltage-gated K+ channels are activated, resulting in a net outward movement of K+ ions, which repolarizes the membrane potential towards the resting membrane potential. Repolarization of the membrane potential continues, resulting in an undershoot phase or absolute refractory period. The undershoot phase occurs because unlike voltage-gated sodium channels, voltage-gated potassium channels inactivate much more slowly. Nevertheless, as more voltage-gated K+ channels become inactivated, the membrane potential recovers to its normal resting steady state.
Structure and formation of synapses
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Illustration of the major elements in a prototypical synapse. Synapses allow nerve cells to communicate with one another through axons and dendrites, converting electrical impulses into chemical signals.
Neurons communicate with one another via synapses. Synapses are specialized junctions between two cells in close apposition to one another. In a synapse, the neuron that sends the signal is the presynaptic neuron and the target cell receives that signal is the postsynaptic neuron or cell. Synapses can be either electrical or chemical. Electrical synapses are characterized by the formation of gap junctions that allow ions and other organic compound to instantaneously pass from one cell to another.[2] Chemical synapses are characterized by the presynaptic release of neurotransmitters that diffuse across a synaptic cleft to bind with postsynaptic receptors. A neurotransmitter is a chemical messenger that is synthesized within neurons themselves and released by these same neurons to communicate with their postsynaptic target cells. A receptor is a transmembrane protein molecule that a neurotransmitter or drug binds. Chemical synapses are slower than electrical synapses.
Neurotransmitter transporters, receptors, and signaling mechanisms
After neurotransmitters are synthesized, they are packaged and stored in vesicles. These vesicles are pooled together in terminal boutons of the presynaptic neuron. When there is a change in voltage in the terminal bouton, voltage-gated calcium channels embedded in the membranes of these boutons become activated. These allow Ca2+ ions to diffuse through these channels and bind with synaptic vesicles within the terminal buttons. Once bounded with Ca2+, the vesicles dock and fuse with the presynaptic membrane, and release neurotransmitters into the synaptic cleft by a process known as exocytosis. The neurotransmitters then diffuse across the synaptic cleft and binds to postsynaptic receptors embedded on the postsynaptic membrane of another neuron. There are two families of receptors: ionotropic and metabotropic receptors. Ionotropic receptors are a combination of a receptor and an ion channel. When ionotropic receptors are activated, certain ion species such as Na+ to enter the postsynaptic neuron, which depolarizes the postsynaptic membrane. If more of the same type of postsynaptic receptors are activated, then more Na+ will enter the postsynaptic membrane and depolarize cell. Metabotropic receptors on the other hand activate second messenger cascade systems that result in the opening of ion channel located some place else on the same postsynaptic membrane. Although slower than ionotropic receptors that function as on-and-off switches, metabotropic receptors have the advantage of changing the cell's responsiveness to ions and other metabolites, examples being Gamma Amino-Butyric Acid (inhibitory transmitter), Glutamic Acid (excitatory transmitter), Dopamine, Norepinephrine, Epinephrine, Melanin, Serotonin, Melatonin, and Substance-P.Postsynaptic depolarizations can be either excitatory or inhibitory. Those that are excitatory are referred to as excitatory postsynaptic potential (EPSP). Alternatively, some postsynaptic receptors allow Cl- ions to enter the cell or K+ ions to leave the cell, which results in an inhibitory postsynaptic potential (IPSP). If the EPSP is dominant, the threshold of excitation in the postynaptic neuron may be reached, resulting in the generation and propagation of an action potential in the postynaptic neuron.
Synaptic plasticity
Synaptic plasticity is the process whereby strengths of synaptic connections are altered. For example, long-term changes in synaptic connection may result in more postynaptic receptors being embedded in the postsynaptic membrane, resulting in the strengthening of the synapse. Synaptic plasticity is also found to be the neural mechanism that underlies learning and memory.Sensory systems
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Gray's FIG. 722– Scheme showing central connections of the optic nerves and optic tracts.
The auditory system is a sensory system for the sense of hearing. It consists of the outer ear, the middle ear, and the inner ear.
The olfactory system is the sensory system used for olfaction. The accessory olfactory system senses pheromones. The olfactory system is often spoken of along with the gustatory system as the chemosensory senses because both transduce chemical signals into perception. Linda B. Buck and Richard Axel won the 2004 Nobel Prize in Physiology or Medicine for their work on the olfactory system.
The visual system is the part of the nervous system which allows organisms to see. It interprets the information from visible light to build a representation of the world surrounding the body. The visual system has the complex task of (re)constructing a three dimensional world from a two dimensional projection of that world. Note that different species are able to see different parts of the light spectrum; for example, some can see into the ultraviolet, while others can see into the infrared.
Neural development
Neural development is the process whereby the nervous system grows and develops. Aside from the primitive gut, the nervous system is the first organ system to develop and the last system to finish. Development of the nervous system begins when the ectoderm thickens to form a neural plate. The neural plate in turns thickens to form the neural tube, which then twists, turns and kinks to form the three primary brain vesicles and five secondary brain vesicles. Within this neural tube, totipotent cells migrate and differentiate into neurons and glial cells. The neural plate will form the neural tubeReferences
1. ^ Shepard, G. M. (1994). Neurobiology. 3rd Ed. Oxford University Press. ISBN 0-19-508843-3
2. ^ Martin, A. R., Wallace, B. G., Fuchs, P. A. & Nicholls, J. G. (2001). From Neuron to Brain: A Cellular and Molecular Approach to the Function of the Nervous System. 4th Ed. Sinauer Associates. ISBN 0-87893-439-1
2. ^ Martin, A. R., Wallace, B. G., Fuchs, P. A. & Nicholls, J. G. (2001). From Neuron to Brain: A Cellular and Molecular Approach to the Function of the Nervous System. 4th Ed. Sinauer Associates. ISBN 0-87893-439-1
External links
- Journal of Neurobiology — Original research articles on the nervous system
- Neuroscience News — Neuroscience news, neurobiology articles, links, forum, books and gifts
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nervous system of an animal coordinates the activity of the muscles, monitors the organs, constructs and also stops input from the senses, and initiates actions. Prominent parts of a nervous system include neurons and nerves, which are used in coordination.
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Biology (from Greek: βίος, bio, "life"; and λόγος, logos, "knowledge"), also referred to as the biological sciences, is the scientific study of life.
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Neuroscience is a field that is devoted to the scientific study of the nervous system. Such studies may include the structure, function, evolutionary history, development, genetics, biochemistry, physiology, pharmacology, and pathology of the nervous system.
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Computational neuroscience is an interdisciplinary science that links the diverse fields of neuroscience, cognitive science, electrical engineering, computer science, physics and mathematics. Historically, the term was introduced by Eric L.
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Cognitive neuroscience is an academic field concerned with the scientific study of biological mechanisms underlying cognition, with a specific focus on the neural substrates of mental processes and their behavioral manifestations.
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biological psychology or psychobiology[1] is the application of the principles of biology to the study of mental processes and behavior. A psychobiologist, for instance, may compare the imprinting behavior in goslings to the early attachment behavior in human
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Biological psychiatry, or biopsychiatry is an approach to psychiatry that aims to understand mental disorder in terms of the biological function of the nervous system.
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Neurology is a branch of medicine dealing with disorders of the nervous system. Medical professionals (such as Biomedical Doctors and Physicians) specializing in the field of neurology are called neurologists
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Neuropsychology is an interdisciplinary branch of psychology and neuroscience that aims to understand how the structure and function of the brain relate to specific psychological processes and overt behaviors.
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Neurobiologist is a life scientist who is devoted to the study of neurobiology. Although the term is sometimes synonymous with neuroscientist, neurobiologists nevertheless take a biological approach to the study of the nervous system.
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Neurons (also known as neurones and nerve cells) are electrically excitable cells in the nervous system that process and transmit information. In vertebrate animals, neurons are the core components of the brain, spinal cord and peripheral nerves.
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Glial cells, commonly called neuroglia or simply glia (greek for "glue"), are non-neuronal cells that provide support and nutrition, maintain homeostasis, form myelin, and participate in signal transmission in the nervous system.
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Neurons (also known as neurones and nerve cells) are electrically excitable cells in the nervous system that process and transmit information. In vertebrate animals, neurons are the core components of the brain, spinal cord and peripheral nerves.
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For the dendritic crystal structure, see .
Dendrites (from Greek dendron, “tree”) are the branched projections of a neuron that act to conduct the electrical stimulation received from other neural cells to the cell body, or
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Photoreceptor can refer to:
In anatomy/cell biology:
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In anatomy/cell biology:
- Photoreceptor cell: a photosensitive cell, most commonly referring to a specialized type of neuron found in the retina of vertebrate eyes that is capable of phototransduction;
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Sir Alan Lloyd Hodgkin, OM, KBE, FRS (born February 5, 1914, Banbury, Oxfordshire, England [1]; died December 20, 1998 Cambridge [2]) was a British physiologist and biophysicist, who won the 1963 Nobel Prize in Physiology or Medicine for his work with Andrew
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Sir Andrew Fielding Huxley, OM, FRS (born 22 November 1917, Hampstead, London [1]) is an English physiologist and biophysicist, who won the 1963 Nobel Prize in Physiology or Medicine for his work with Alan Lloyd Hodgkin on the basis of nerve action potentials, the
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Hodgkin-Huxley Model is a scientific model that describes how action potentials in neurons are initiated and propagated. It is a set of nonlinear ordinary differential equations that approximates the electrical characteristics of excitable cells such as neurons and cardiac myocytes.
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An action potential is a "spike" of electrical discharge that travels along the membrane of a cell. Action potentials are an essential feature of animal life, rapidly carrying information within and between tissues. They also occur in some plants.
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synapse. Synapses allow nerve cells to communicate with one another through axons and dendrites, converting electrical impulses into chemical signals.]]
Chemical synapses
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Chemical synapses
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Communication is a process that allows organisms to exchange information by several methods. Communication requires that all parties understand a common language that is exchanged with each other.
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Exocytosis (ek-soh-sy-TOH-sis) is the process by which a cell directs secretory vesicles to the cell membrane. These membrane-bound vesicles contain soluble proteins to be secreted to the extracellular environment, as well as membrane proteins and lipids that are sent to become
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Gaba may refer to:
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- GABA, the gamma-aminobutyric acid neurotransmitter
- GABA receptor, in biology, receptors with GABA as their endogenous ligand
- Gabâ or gabaa (Philippines), the concept of negative karma of the Cebuano people
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Glutamic acid or glutamate (abbreviated as Glu or E; Glx or Z represents either glutamic acid or glutamine), is the protonated form of glutamate (the anion). Glutamate is one of the 20 proteinogenic amino acids.
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Dopamine is a hormone and neurotransmitter occurring in a wide variety of animals, including both vertebrates and invertebrates. In chemical structure, it is a phenethylamine.
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Norepinephrine (INN)(abbr. norepi or NE) or noradrenaline (BAN) is a catecholamine and a phenethylamine with chemical formula C8H11NO3. The natural stereoisomer is L -(−)-(R)-norepinephrine.
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Epinephrine (INN) (IPA: [ˌɛpɪˈnɛfrən]) or adrenaline (European Pharmacopoeia and BAN) (IPA: [əˈdrɛnələn]
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Broadly, melanin is any of the polyacetylene, polyaniline, and polypyrrole "blacks" and "browns" or their mixed copolymers. The most common form of biological melanin is a polymer of either or both of two monomer molecules: indolequinone, and dihydroxyindole carboxylic acid.
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Serotonin (pronounced IPA: /ˌsɛrəˈtoʊnən/) (5-hydroxytryptamine, or 5-HT) is a monoamine neurotransmitter synthesized in serotonergic neurons in the central nervous system (CNS) and
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