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Encyclopedia > Motor neuron
Motor neuron
Motor neuron - Section through the spinal cord. Motor neuron projection through ventral root is shown in red.
Section through the spinal cord. Motor neuron projection through ventral root is shown in red.
Location Ventral horn of the spinal cord
Function Excitatory projection (to NMJ)
Neurotransmitter ACh
Morphology Projection neuron
Presynaptic connections M1 via the Corticospinal tract
Postsynaptic connections Muscle fibers and other neurons

In vertebrates, the term motor neuron (or motoneuron) classically applies to neurons located in the central nervous system (CNS) which project their axons outside the CNS and directly or indirectly control muscles. Motor neuron is often synonymous with efferent neuron. Image File history File links Medulla_spinalis_-_Section_-_English. ... In anatomy and neurology, the ventral root is the efferent motor root of a spinal nerve. ... The anterior horn is the anterior division of the lateral ventricle of the brain. ... The Spinal cord nested in the vertebral column. ... Electron micrograph showing a cross section through the neuromuscular junction. ... ACH is a three letter abbreviation that can refer to: Acetylcholine (ACh), a neurotransmitter Achondroplasia, a type of genetic disorder that is a common cause of dwarfism Achnashellach railway station (United Kingdom), as the National Rail code for the station Acholi language (ach), as the ISO 639 code for the... The term morphology in biology refers to the outward appearance (shape, structure, colour, pattern) of an organism or taxon and its component parts. ... The primary motor area is a group of networked cells in mammalian brains that controls movements of specific body parts associated with cell groups in that area of the brain. ... The corticospinal or pyramidal tract is a massive collection of axons that travel between the cerebral cortex of the brain and the spinal cord. ... A simplified, global view of a neuromuscular junction: 1. ... Drawing by Santiago Ramón y Cajal of neurons in the pigeon cerebellum. ... This article does not cite any references or sources. ... Neurons (also called nerve cells) are the primary cells of the nervous system. ... A diagram showing the CNS: 1. ... An axon, or nerve fiber, is a long slender projection of a nerve cell, or neuron, which conducts electrical impulses away from the neurons cell body or soma. ... A top-down view of skeletal muscle Muscle (from Latin musculus little mouse [1]) is contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. ... In vertebrates, motoneurons (also called motor neurons) are efferent neurons that originate in the spinal cord and synapse with muscle fibers to facilitate muscle contraction and with muscle spindles to modify proprioceptive sensitivity. ...

Contents

Anatomy and physiology

Branch of NS Position Neurotransmitter
Somatic n/a Acetylcholine
Parasympathetic Preganglionic Acetylcholine
Parasympathetic Ganglionic Acetylcholine
Sympathetic Preganglionic Acetylcholine
Sympathetic Ganglionic Norepinephrine*
*Except fibers to sweat glands and certain blood vessels
Motoneuron neurotransmitters

According to their targets, motoneurons are classified into three broad categories: In humans, there are four kinds of sudoriferous or sweat glands which differ greatly in both the composition of the sweat and its purpose. ... f you all The blood vessels are part of the circulatory system and function to transport blood throughout the body. ...


"Somatic motoneurons", which directly innervate skeletal muscles, involved in locomotion (such as muscles of the limbs, abdominal and intercostal muscles). Structure of a skeletal muscle Skeletal muscle is a type of striated muscle, attached to the skeleton. ... Intercostal muscles are several groups of muscles that run between the ribs. ...


Special visceral motoneurons — also called “branchial motoneurons”— which directly innervate branchial muscles (that motorize the gills in fish and the face and neck in land vertebrates). Special visceral efferent (SVE) refers to efferent nerves which supply muscles which derived from the branchial arches. ... Branchiomeric Muscles are striated muscles of the head and neck. ... In aquatic organisms, gills are a respiratory organ for the extraction of oxygen from water and for the excretion of carbon dioxide. ... Typical classes Petromyzontidae (lampreys) Placodermi - extinct Chondrichthyes (cartilaginous fish) Acanthodii - extinct Actinopterygii (ray-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ...


General visceral motoneurons — "visceral motoneurons" for short— which indirectly innervate smooth muscles of the viscera (like the heart, or the muscles of the arteries): they synapse onto neurons located in ganglia of the autonomic nervous system (sympathetic and parasympathetic), located in the peripheral nervous system (PNS), which themselves directly innervate visceral muscles (and also some gland cells). The general visceral efferent fibers (GVE or sympathetic efferent fibers), probably arise from cells in the lateral column or the base of the anterior column and emerge through the anterior roots and white rami communicantes. ... Smooth muscle is a type of non-striated muscle, found within the walls of hollow organs; such as blood vessels, bladders, uteri. ... In anatomy, the viscera are the internal organs of an animal, in particular the internal organs of the head, thorax and abdomen. ... The heart and lungs, from an older edition of Grays Anatomy. ... Section of an artery An artery or arterial is also a class of highway. ... Illustration of the major elements in a prototypical synapse. ... GÃ…NGLÃŽÃ… is a 1 man electronic grindcore band from Los Angeles California that began in August of 1999. ... This article or section is in need of attention from an expert on the subject. ... Grays FIG. 838– The right sympathetic chain and its connections with the thoracic, abdominal, and pelvic plexuses. ... Anatomy and Physiology of the A.N.S. In contrast to the voluntary nervous system, the involuntary or autonomic nervous system is responsible for homeostasis, maintaining a relatively constant internal environment by controlling such involuntary functions as digestion, respiration, and metabolism, and by modulating blood pressure. ... The Peripheral nervous system resides or extends outside the CNS central nervous system (the brain and spinal cord) to serve the limbs and organs. ...


In other words:

  • the motor command of skeletal and branchial muscles is monosynaptic (involving only one motoneuron —respectively “somatic “ and “branchial”— which synapses onto the muscle).
  • the command of visceral muscles is disynaptic (involving two neurons: the “general visceral motoneuron” located in the CNS, which synapses onto a ganglionic neuron, located in the PNS, which synapses onto the muscle).

It could be argued that, in the command of visceral muscles, the ganglionic neuron —parasympathetic or sympathetic— is the real “motoneuron”, being the one that directly innervates the muscle (while the “general visceral motoneuron” is, strictly speaking, a “preganglionic” neuron). But, for historical reasons, the term motoneuron is reserved for the CNS neuron. This article or section does not cite any references or sources. ... Smooth muscle Layers of Esophageal Wall: 1. ... Anatomy and Physiology of the A.N.S. In contrast to the voluntary nervous system, the involuntary or autonomic nervous system is responsible for homeostasis, maintaining a relatively constant internal environment by controlling such involuntary functions as digestion, respiration, and metabolism, and by modulating blood pressure. ... The word sympathetic means different things in different contexts. ... In the autonomic nervous system, fibers from the CNS to the ganglion are known as preganglionic fibers. ...


All motoneurons are cholinergic (that is, release the neurotransmitter acetylcholine). Parasympathetic ganglionic neurons are also cholinergic, while most sympathetic ganglionic neurons are noradrenergic (that is, release the neurotransmitter noradrenaline). (see Table) A synapse is cholinergic if it uses acetylcholine as its neurotransmitter. ... The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. ... Norepinephrine (INN) or noradrenaline (BAN) is a catecholamine and a phenethylamine with chemical formula C8H11NO3. ... Norepinephrine, known as noradrenaline outside the USA, is a catecholamine and a phenethylamine with chemical formula C8H11NO3. ...


Function

The interface between a motoneuron and muscle fiber is a specialized synapse called the neuromuscular junction. Upon adequate stimulation, the motoneuron releases a flood of neurotransmitters that bind to postsynaptic receptors and triggers a response in the muscle fiber. Illustration of the major elements in a prototypical synapse. ... A neuromuscular junction is the junction of the axon terminal of a motoneuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscles surface. ... Chemical structure of D-aspartic acid, a common amino acid neurotransmitter. ... In biochemistry, a receptor is a protein on the cell membrane or within the cytoplasm or cell nucleus that binds to a specific molecule (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates the cellular response to the ligand. ...

  • In invertebrates, depending on the neurotransmitter released and the type of receptor it binds, the response in the muscle fiber could either be excitatory or inhibitory.
  • For vertebrates, however, the response of a muscle fiber to a neurotransmitter can only be excitatory, in other words, contractile. Muscle relaxation and inhibition of muscle contraction in verterbrates is obtained only by inhibition of the motoneuron itself. Although muscle innervation may eventually paly a role in the maturation of motor activity. This is why muscle relaxants work by acting on the motoneurons that innervate muscles (by decreasing their electrophysiological activity) or on cholinergic neuromuscular junctions, rather than on the muscles themselves.

Invertebrate is a term coined by Chevalier de Lamarck to describe any animal without a backbone or vertebra, like insects, squids and worms. ... Typical classes Petromyzontidae (lampreys) Placodermi - extinct Chondrichthyes (cartilaginous fish) Acanthodii - extinct Actinopterygii (ray-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ... Chemical structure of D-aspartic acid, a common amino acid neurotransmitter. ... In medicine, a muscle relaxant is a drug that causes skeletal muscle contraction to cease. ... Current Clamp is a common technique in electrophysiology. ... The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. ... A neuromuscular junction is the junction of the axon terminal of a motoneuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscles surface. ...

Somatic motoneurons

Somatic motoneurons are further subdivided into two types: alpha efferent neurons and gamma efferent neurons. (Both types are called efferent to indicate the flow of information from the central nervous system (CNS) to the periphery.) Efferent nerve fibers carry information away from the brain. ... A diagram showing the CNS: 1. ... The Peripheral nervous system resides or extends outside the CNS central nervous system (the brain and spinal cord) to serve the limbs and organs. ...

In addition to voluntary skeletal muscle contraction, alpha motoneurons also contribute to muscle tone, the continuous force generated by noncontracting muscle to oppose stretching. When a muscle is stretched, sensory neurons within the muscle spindle detect the degree of stretch and send a signal to the CNS. The CNS activates alpha motoneurons in the spinal cord which cause extrafusal muscle fibers to contract and thereby resist further stretching. This process is also called the stretch reflex. Alpha motor neurons (α-MNs) are large lower motor neurons of the brainstem and spinal cord. ... Extrafusal muscle fibers are served by axons of the alpha motor neurons. ... γ-motoneurons (gamma-motoneurons or motor neurons) are a component of the fusimotor system, the system by which the CNS controls muscle spindle sensitivity. ... Intrafusal fibers are muscle fibers that comprise the muscle spindle. ... A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ... Bodybuilder showing highly developed muscle tone. ... The mechanism of the reflex arc Sensory neurons (or neurones) are nerve cells within the nervous system responsible for converting external stimuli from the organisms environment into internal [[electrical poop is responsible for it aright underlie motor reflex loops and several forms of involuntary behavior, including pain avoidance. ... A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ... It is reflex muscle contraction in response of its stretch. ...


Gamma motoneurons regulate the sensitivity of the spindle to muscle stretching. With activation of gamma neurons, intrafusal muscle fibers contract so that only a small stretch is required to activate spindle sensory neurons and the stretch reflex.


Motor units

A single motoneuron may synapse with one or more muscle fibers. The motoneuron and all of the muscle fibers to which it connects is a motor unit. A motor unit is a group of cells under the control of a single motor neuron; groups of motor units work together, as a single muscle. ...


See also

A neuromuscular junction is the junction of the axon terminal of a motoneuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscles surface. ... A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ... A motor unit is a group of cells under the control of a single motor neuron; groups of motor units work together, as a single muscle. ... The motor neurone diseases (MND) are a group of progressive neurological disorders that destroy motor neurones, the cells that control voluntary muscle activity such as speaking, walking, breathing, and swallowing. ... Motor nerves allow the brain to stimulate muscle contraction. ... In the nervous system, efferent nerves otherwise known as motor or effector neuron carry nerve impulses away from the central nervous systemto effectors - either muscles or glands. ... In the nervous system, efferent nerves otherwise known as motor or effector neuron carry nerve impulses away from the central nervous systemto effectors - either muscles or glands. ...

References

  • Sherwood, L. (2001). Human Physiology: From Cells to Systems (4 ed.). California: Brooks/Cole.
  • Marieb, E. N., Mallatt, J. (1997). Human Anatomy (2 ed.). California: Benjamin/Cummings.

  Results from FactBites:
 
BrainConnection.com - The Anatomy of Movement (932 words)
Fibers in the corticospinal tract synapse onto motor neurons and interneurons in the ventral horn of the spine.
Furthermore, neurons of extensors (muscles that increase the joint angle such as the triceps muscle) are found near the edge of the gray matter, but the flexors (muscles which decrease the joint angle such as the biceps muscle) are more interior.
The motor unit is composed of the motor neuron, its axon and the muscle fibers it innervates.
Motor Systems (1173 words)
The upper motor neuron axon extends all the way from the brain down to the spinal cord, a distance 1-3 feet or more, and the lower motor neuron axon extends from the spinal cord to the skeletal muscles of the arms or legs, a distance 4-5 feet in very tall people.
Neurons which control movements of the face and mouth are located near the Sylvian or lateral fissue and neurons which control the muscles of the thighs and legs are located near the medial longitudinal fissure and within the central sulcus.
Upper motor neurons which innervate the muscles of the face and head are located near the lateral fissure of the brain.
  More results at FactBites »

 
 

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