Orthodromic

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An orthodromic impulse runs along an axon in its anterograde direction, away from the soma. [1]

Action potential A process in which membrane potential cycles through a depolarizing spike, triggered in response to depolarization above some threshold, followed by repolarization. This cycle is driven by the flow of ions through various voltage gated channels with

In physiology, an action potential occurs when the membrane potential of a specific axon location rapidly rises and falls: this depolarisation then causes adjacent locations to similarly depolarise. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, endocrine cells, glomus cells, and in some plant cells.

Axon The long process of a neuron that conducts nerve impulses, usually away from the cell body to the terminals and varicosities, which are sites of storage and release of neurotransmitter.

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 has caused many inherited and acquired neurological disorders which can 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.

Soma (biology) The portion of the cell soma (neuronal cell body) that excludes the nucleus.

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. The word 'soma' comes from the Greek 'σῶμα', meaning 'body'. 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 millimetre for some of the smallest and largest neurons of invertebrates, respectively.

In the heart, orthodromic may also refer to an impulse going in the correct direction from the dendrites to axon terminal (from the atria to the ventricles) in contrast to some impulses in re-entry.

Heart organ for the circulation of blood in animal circulatory systems

The heart is a muscular organ in most animals, which pumps blood through the blood vessels of the circulatory system. Blood provides the body with oxygen and nutrients, as well as assisting in the removal of metabolic wastes. In humans, the heart is located between the lungs, in the middle compartment of the chest.

Atrium (heart) chamber of the heart

The atrium is the upper chamber through which blood enters the heart. There are two atria in the human heart – the left atrium connected to the lungs, and the right atrium connected to the venous circulation. The atria receive blood, and when the heart muscle contracts they pump blood to the ventricles. All animals with a closed circulatory system have at least one atrium.

Ventricle (heart) chamber of the heart

A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The atrium primes the pump. Interventricular means between the ventricles, while intraventricular means within one ventricle.

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Dendrite neuron projection that has a short, tapering, often branched, morphology, receives and integrates signals from other neurons or from sensory stimuli, and conducts a nerve impulse towards the axon or the cell body

Dendrites, also dendrons, are branched protoplasmic extensions of a nerve cell that propagate 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. Dendrites play a critical role in integrating these synaptic inputs and in determining the extent to which action potentials are produced by the neuron. Dendritic arborization, also known as dendritic branching, is a multi-step biological process by which neurons form new dendritic trees and branches to create new synapses. The morphology of dendrites such as branch density and grouping patterns are highly correlated to the function of the neuron. Malformation of dendrites is also tightly correlated to impaired nervous system function. Some disorders that are associated with the malformation of dendrites are autism, depression, schizophrenia, Down syndrome and anxiety.

Neuron electrically excitable cell

A neuron, also known as a neurone or nerve cell, is an electrically excitable cell that communicates with other cells via specialized connections called synapses. It is the main component of nervous tissue. All animals except sponges and placozoans have neurons, but other multicellular organisms such as plants do not.

Nervous tissue main component of the nervous system

Nervous tissue, also called neural tissue or nerve tissue, is the main tissue component of the nervous system. The nervous system regulates and controls bodily functions and activity and consists of two parts: the central nervous system (CNS) comprising the brain and spinal cord, and the peripheral nervous system (PNS) comprising the branching peripheral nerves. It is composed of neurons, or nerve cells, which receive and transmit impulses, and neuroglia, also known as glial cells or glia, which assist the propagation of the nerve impulse as well as provide nutrients to the neurons.

An artificial neuron is a mathematical function conceived as a model of biological neurons, a neural network. Artificial neurons are elementary units in an artificial neural network. The artificial neuron receives one or more inputs and sums them to produce an output. Usually each input is separately weighted, and the sum is passed through a non-linear function known as an activation function or transfer function. The transfer functions usually have a sigmoid shape, but they may also take the form of other non-linear functions, piecewise linear functions, or step functions. They are also often monotonically increasing, continuous, differentiable and bounded. The thresholding function has inspired building logic gates referred to as threshold logic; applicable to building logic circuits resembling brain processing. For example, new devices such as memristors have been extensively used to develop such logic in recent times.

Pyramidal cell

Pyramidal cells, or pyramidal neurons, are a type of multipolar neuron found in areas of the brain including the cerebral cortex, the hippocampus, and the amygdala. Pyramidal neurons are the primary excitation units of the mammalian prefrontal cortex and the corticospinal tract. Pyramidal neurons are also one of two cell types where the characteristic sign, Negri bodies, are found in post-mortem rabies infection. Pyramidal neurons were first discovered and studied by Santiago Ramón y Cajal. Since then, studies on pyramidal neurons have focused on topics ranging from neuroplasticity to cognition.

Axoplasm is the cytoplasm within the axon of a neuron. Neurites contain about 99.6% of the cell’s cytoplasm, and 99.7% of that is in the axons.

Basket cell

Basket cells are inhibitory GABAergic interneurons of the brain, found throughout different regions of the cortex and cerebellum.

Pseudounipolar neuron

A pseudounipolar neuron is a kind of sensory neuron in the peripheral nervous system. This neuron contains an axon that has split into two branches; one branch runs to the periphery and the other to the spinal cord.

Axonal transport The directed movement of organelles or molecules along microtubules in axons.

Axonal transport, also called axoplasmic transport or axoplasmic flow, is a cellular process responsible for movement of mitochondria, lipids, synaptic vesicles, proteins, and other cell parts to and from a neuron's cell body, through the cytoplasm of its axon. Since some axons are on the order of meters long, neurons cannot rely on diffusion to carry products of the nucleus and organelles to the end of their axons. Axonal transport is also responsible for moving molecules destined for degradation from the axon back to the cell body, where they are broken down by lysosomes.

Cochlear nerve

The cochlear nerve is one of two parts of the vestibulocochlear nerve, a cranial nerve present in amniotes, the other part being the vestibular nerve. The cochlear nerve carries auditory sensory information from the cochlea of the inner ear directly to the brain. The other portion of the vestibulocochlear nerve is the vestibular nerve, which carries spatial orientation information to the brain from the semicircular canals, also known as semicircular ducts.

An antidromic impulse in an axon refers to conduction opposite of the normal (orthodromic) direction. That is, it refers to conduction along the axon away from the axon terminal(s) and towards the soma. For most neurons, their dendrites, soma, or axons are depolarized forming an action potential that moves from the starting point of the depolarization along the axons of the neuron (orthodromic). Antidromic activation is often induced experimentally by direct electrical stimulation of a presumed target structure. Antidromic activation is often used in a laboratory setting to confirm that a neuron being recorded from projects to the structure of interest.

A neurite or neuronal process refers to any projection from the cell body of a neuron. This projection can be either an axon or a dendrite. The term is frequently used when speaking of immature or developing neurons, especially of cells in culture, because it can be difficult to tell axons from dendrites before differentiation is complete.

Neural backpropagation is the phenomenon in which after the action potential of a neuron creates a voltage spike down the axon another impulse is generated from the soma and propagates toward to the apical portions of the dendritic arbor or dendrites, from which much of the original input current originated. In addition to active backpropagation of the action potential, there is also passive electrotonic spread. While there is ample evidence to prove the existence of backpropagating action potentials, the function of such action potentials and the extent to which they invade the most distal dendrites remains highly controversial.

Axon reflex

The axon reflex is the response stimulated by peripheral nerves of the body that travels away from the nerve cell body and branches to stimulate target organs. Reflexes are single reactions that respond to a stimulus making up the building blocks of the overall signaling in the body's nervous system. Neurons are the excitable cells that process and transmit these reflex signals through their axons, dendrites, and cell bodies. Axons directly facilitate intercellular communication projecting from the neuronal cell body to other neurons, local muscle tissue, glands and arterioles. In the axon reflex, signaling starts in the middle of the axon at the stimulation site and transmits signals directly to the effector organ skipping both an integration center and a chemical synapse present in the spinal cord reflex. The impulse is limited to a single bifurcated axon, or a neuron whose axon branches into two divisions and does not cause a general response to surrounding tissue.

Dendritic spike

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, 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 terminal Terminal inflated portion of the axon, containing the specialized apparatus necessary to release neurotransmitters. The axon terminus is considered to be the whole region of thickening and the terminal bouton is a specialized region of it.

Axon terminals are distal terminations of the telodendria (branches) of an axon. An axon, also called a nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses called action potentials away from the neuron's cell body, or soma, in order to transmit those impulses to other neurons, muscle cells or glands.

Granule cell

The name granule cell has been used for a number of different types of neuron whose only common feature is that they all have very small cell bodies. Granule cells are found within the granular layer of the cerebellum, the dentate gyrus of the hippocampus, the superficial layer of the dorsal cochlear nucleus, the olfactory bulb, and the cerebral cortex.

Viral neuronal tracing

Viral neuronal tracing is the use of a virus to trace neural pathways, providing a self-replicating tracer. Viruses have the advantage of self replication over molecular tracers, but can also spread too quickly and cause degradation of neural tissue. Viruses which can infect the nervous system, called Neurotropic viruses, spread through spatially close assemblies of neurons through synapses, allowing for their use in studying functionally connected neural networks. The use of viruses to label functionally connected neurons stems from work done by Albert Sabin who developed a bioassay which could assess the infection of viruses across neurons. Subsequent research allowed for incorporation of Immunohistochemical techniques to systematically label neuronal connections. To date, viruses have been used to study multiple circuits in the nervous system.

References

  1. EYZAGUIRRE, C; KUFFLER, SW (Sep 20, 1955). "Further study of soma, dendrite, and axon excitation in single neurons". The Journal of General Physiology. 39 (1): 121–53. doi:10.1085/jgp.39.1.121. PMC   2147522 Lock-green.svg. PMID   13252238 . Retrieved 28 December 2012.