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Encyclopedia > Alpha motor neuron
Alpha motor neuron
Alpha motor neurons are derived from the basal plate (basal lamina) of the developing embryo.
[[Image:|200px|center|]]
Latin '
Gray's subject #190
System Central nervous system
Precursor Basal plate
MeSH A08.186.854.080
Dorlands/Elsevier m_20/12542868

Alpha motor neurons (α-MNs) are large lower motor neurons of the brainstem and spinal cord. They innervate extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their contraction. Alpha motor neurons are distinct from gamma motor neurons, which innervate intrafusal muscle fibers of muscle spindles. Embryos (and one tadpole) of the wrinkled frog (Rana rugosa). ... Latin is an ancient Indo-European language originally spoken in the region around Rome called Latium. ... In biology, an organ is a group of tissues which perform some function. ... A diagram showing the CNS: 1. ... Embryology is the branch of developmental biology that studies embryos and their development. ... Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. ... Elseviers logo Elsevier, the worlds largest publisher of medical and scientific literature, forms part of the Reed Elsevier group. ... Lower motor neurons (LMNs) are the motoneurons connecting the brainstem and spinal cord to muscle fibers, bringing the nerve impulses from the upper motor neurons out to the muscles. ... The brain stem is the stalk of the brain below the cerebral hemispheres. ... Cross-section through cervical spinal cord. ... Extrafusal muscle fibers are served by axons of the alpha motor neurons. ... A top-down view of skeletal muscle Skeletal muscleis a type of striated muscle, attached to the skeleton. ... A top-down view of skeletal muscle A muscle contraction (also known as a muscle twitch or simply twitch) occurs when a muscle cell (called a muscle fiber) shortens. ... 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. ...


While their cell bodies are found in the central nervous system (CNS), alpha motor neurons are also considered part of the somatic nervous system—a branch of the peripheral nervous system (PNS)—because their axons extend into the periphery to innervate skeletal muscles. The cell body or soma is a structure in a neuron consisting of the main part of the cell and containing the nucleus. ... A diagram showing the CNS: 1. ... The somatic nervous system is that part of the peripheral nervous system associated with the voluntary control of body movements through the action of skeletal muscles, and also reception of external stimuli. ... The peripheral nervous system or PNS, is part of the nervous system, and consists of the nerves and neurons that reside or extend outside the central nervous system--to serve the limbs and organs, for example. ... An axon, or nerve fiber, is a long slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... A top-down view of skeletal muscle Skeletal muscleis a type of striated muscle, attached to the skeleton. ...


An alpha motor neuron and the muscle fibers it innervates is a motor unit. A motor neuron pool contains all the alpha motor neurons involved in contracting a single muscle. 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. ...

Contents


Location

Alpha motor neurons innervating the head and neck are found in the brainstem; the remaining α-MNs innervate the rest of the body and are found in the spinal cord. Because there are fewer muscles in the head and neck than in the rest of the body, there are more α-MNs in the spinal cord than in the brainstem. A human head In anatomy, the head of an animal is the anterior part (from anatomical position) that usually comprises the brain, eyes, ears, nose, and mouth (all of which aid in various sensory functions, such as sight, hearing, smell, and taste). ... The neck is the part of the body on many limbed vertebrates that distinguishes the head from the torso or trunk. ... The brain stem is the stalk of the brain below the cerebral hemispheres. ... Cross-section through cervical spinal cord. ...


In general, α-MNs on one side of the brainstem or spinal cord innervate muscles on that same side of body. The one exception is the trochlear nucleus in the brainstem, which innervates the superior oblique muscle of the eye on the opposite side of the face. The nucleus of the trochlear nerve is located in the midbrain, at the level of the inferior colliculus. ... The superior oblique muscle is a muscle in the orbit that causes the eye to look downwards when it is already directed medially (looking towards the nose). ...


Brainstem

In the brainstem, α-MNs and other neurons reside within clusters of cells called nuclei, some of which contain the cell bodies of neurons belonging to the cranial nerves. Not all cranial nerve nuclei contain α-MNs; those that do are motor nuclei, while others are sensory nuclei. Motor nuclei are found throughout the brainstem—medulla, pons, and midbrain—and for developmental reasons are found near the midline of the brainstem. Drawing by Santiago Ramón y Cajal of cells in the pigeon cerebellum. ... In neuroanatomy, a nucleus is a central nervous system structure that is composed mainly of gray matter, and which acts as a hub or transit point for electrical signals in a single neural subsystem. ... Cranial nerves are nerves which start directly from the brainstem instead of the spinal cord. ... A cranial nerve nucleus is a collection of neurons (gray matter) in the brain stem that is associated with one or more cranial nerves. ... The medulla oblongata is the lower portion of the brainstem. ... Position of the pons in the human brain The pons (sometimes pons Varolii after Costanzo Varolio) is a knob on the brain stem. ... In biological anatomy, the mesencephalon (or midbrain) is the middle of three vesicles that arise from the neural tube that forms the brain of developing animals. ...


Generally, motor nuclei found higher in the brainstem (ie, more rostral) innervate muscles that are higher on the face. For example, the oculomotor nucleus contains α-MNs that innervate muscles of the eye, and is found in the midbrain, the most rostral brainstem component. By contrast, the hypoglossal nucleus, which contains α-MNs innervates the tongue, is found in the medulla, the most caudal (ie, towards the bottom) of the brainstem structures. The fibers of the oculomotor nerve arise from a nucleus in the midbrain, which lies in the gray substance of the floor of the cerebral aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle. ... The hypoglossal nucleus extends the length of the medulla, and being a motor nucleus, is close to the midline. ...


Spinal cord

The corticospinal tract is one of the major descending pathways from the brain to the α-MNs of the spinal cord.
Enlarge
The corticospinal tract is one of the major descending pathways from the brain to the α-MNs of the spinal cord.

In the spinal cord, α-MNs are located within the gray matter that forms the ventral horn of the spinal cord. These α-MNs provide the motor component of the spinal nerves that innervate muscles of the body. The corticospinal or pyramidal tract is a massive collection of axons that travel between the cerebral cortex of the brain and the spinal cord. ... Comparative brain sizes In animals, the brain, or encephalon (Greek for in the head), is the control center of the central nervous system. ... Cross-section through cervical spinal cord. ... Grey matter is a category of nervous tissue with many nerve cell bodies and few myelinated axons. ... The anterior horn is the anterior division of the lateral ventricle of the brain. ... The term spinal nerve generally refers to the mixed spinal nerve, which is formed from the dorsal and ventral roots that come out of the spinal cord. ...


As in the brainstem, higher segments of the spinal cord contain α-MNs that innervate muscles higher on the body. For example, the biceps brachii muscle, a muscle of the arm, is innervated by α-MNs in spinal cord segments C5, C6, and C7, which are found rostrally in the spinal cord. On the other hand, the gastrocnemius muscle, one of the muscles of the leg, is innervated by α-MNs within segments S1 and S2, which are found caudally in the spinal cord. In human anatomy, the biceps brachii is a muscle located on the upper arm. ... The gastrocnemius (pronounced ) muscle is a powerful superficial muscle that is in the back part of the lower leg (the calf). ...


Connectivity

Like other neurons, lower motor neurons have both afferent (incoming) and efferent (outgoing) connections. α-MNs receive input from a number of sources, including upper motor neurons, sensory neurons, and interneurons. The primary output of α-MNs is to extrafusal muscle fibers. This afferent and efferent connectivity is required to achieve coordinated muscle activity. Upper motor neurons, or Betz cells, are motoneurons located in the primary motor cortex. ... 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. ... An interneuron (also called relay neuron or association neuron) is a neuron that communicates only to other neurons. ... Extrafusal muscle fibers are served by axons of the alpha motor neurons. ...


Afferent input

Selected pathways between upper motor neurons and alpha motor neurons
UMN origin α-MN target Tract name
Cerebral cortex Brainstem Corticonuclear tract
Cerebral cortex Spinal cord Corticospinal tract
Red nucleus Spinal cord Rubrospinal tract
Vestibular nuclei Spinal cord Vestibulospinal tract
Midbrain tectum Spinal cord Tectospinal tract
Reticular formation Spinal cord Reticulospinal tract

Upper motor neurons (UMNs) send input to α-MNs via several pathways, including (but not limited to) the corticonuclear, corticospinal, and rubrospinal tracts. The corticonuclear and corticospinal tracts are commonly encountered in studies of upper and lower motor neuron connectivity in the control of voluntary movements. Upper motor neurons, or Betz cells, are motoneurons located in the primary motor cortex. ... Location of the cerebral cortex Slice of the cerebral cortex, ca. ... The brain stem is the stalk of the brain below the cerebral hemispheres. ... Cross-section through cervical spinal cord. ... The corticospinal or pyramidal tract is a massive collection of axons that travel between the cerebral cortex of the brain and the spinal cord. ... The red nucleus is a structure in the rostral midbrain involved in motor coordination. ... The rubrospinal tract is part of the indirect extra-pyramidal tract and is responsible for large muscle movement such as the arms and the legs. ... The nuclei of the vestibular nerve. ... The tectospinal tract is part of the indirect extrapyramidal tract and is responsible for coordinating head and eye movements, It is responsible for impulses that are motor. ... Reticular formation is a part of the brain which is involved in stereotypical actions, such as walking, sleeping, and lying down. ... Upper motor neurons, or Betz cells, are motoneurons located in the primary motor cortex. ... The corticospinal or pyramidal tract is a massive collection of axons that travel between the cerebral cortex of the brain and the spinal cord. ... The rubrospinal tract is part of the indirect extra-pyramidal tract and is responsible for large muscle movement such as the arms and the legs. ...


The corticonuclear tract is so named because it connects the cerebral cortex to cranial nerve nuclei. (The corticonuclear tract is also called the corticobulbar tract.) It is via this pathway that upper motor neurons from the cortex descend from the cortex and synapse on α-MNs of the brainstem. Similarly, UMNs of the cerebral cortex are in direct control of α-MNs of the spinal cord via the lateral and ventral corticospinal tracts. Location of the cerebral cortex Slice of the cerebral cortex, ca. ... A cranial nerve nucleus is a collection of neurons (gray matter) in the brain stem that is associated with one or more cranial nerves. ... Illustration of the major elements in a prototypical synapse. ... Cross-section through cervical spinal cord. ... The corticospinal or pyramidal tract is a massive collection of axons that travel between the cerebral cortex of the brain and the spinal cord. ...


The sensory input to α-MNs is extensive and has its origin in Golgi tendon organs, muscle spindles, mechanoreceptors, thermoreceptors, and other sensory neurons in the periphery. These connections provide the structure for the neural circuits that underlie reflexes. There are several types of reflex circuits, the simplest consisting of a single synapse between a sensory neuron and a α-MNs. The knee-jerk reflex is an example of such a monosynaptic reflex. A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ... A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion. ... A thermoreceptor is a sensory receptor that responds to temperature, primarily within the innocuous range. ... 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 reflex action or reflex is a biological control system linking stimulus to response and mediated by a reflex arc. ... The patellar reflex is a reflex employing only two neurons. ...


The most extensive input to α-MNs is from local interneurons, which are the most numerous type of neuron in the spinal cord. Among their many roles, interneurons synapse on α-MNs to create more complex reflex circuitry. One type of interneuron is the Renshaw cell, discussed later. An interneuron (also called relay neuron or association neuron) is a neuron that communicates only to other neurons. ... Cross-section through cervical spinal cord. ... Renshaw cells are located in the spinal cord horn. ...


Efferent output

Alpha motor neurons send fibers that mainly synapse on extrafusal muscle fibers. Other fibers from α-MNs synapse on Renshaw cells, inhibitory interneurons that synapse on the α-MN and limit its activity in order to prevent muscle damage. Extrafusal muscle fibers are served by axons of the alpha motor neurons. ... Renshaw cells are located in the spinal cord horn. ... An interneuron (also called relay neuron or association neuron) is a neuron that communicates only to other neurons. ...


Signaling

Like other neurons, α-MNs transmit signals as action potentials, rapid changes in electrical activity that propagate from the cell body to the end of the axon. To increase the speed at which action potentials travel, α-MN axons have large diameters and are heavily myelinated by both oligodendrocytes and Schwann cells. Oligodendrocytes myelinate the part of the α-MN axon that lies in the central nervous system (CNS), while Schwann cells myelinate the part that lies in the peripheral nervous system (PNS). The transition between the CNS and PNS occurs at the level of the pia mater, the innermost and most delicate layer of meningeal tissue surrounding components of the CNS. A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ... The cell body or soma is a structure in a neuron consisting of the main part of the cell and containing the nucleus. ... An axon, or nerve fiber, is a long slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... In neuroscience, myelin is an electrically insulating phospholipid layer that surrounds the axons of many neurons. ... Oligodendrocytes (from Greek literally meaning few tree cells), or oligodendroglia (Greek, few tree glue)[1], are a variety of neuroglia. ... Schwann cells are a variety of neuroglia that wrap around axons in the peripheral nervous system, forming the myelin sheath. ... A diagram showing the CNS: 1. ... The peripheral nervous system or PNS, is part of the nervous system, and consists of the nerves and neurons that reside or extend outside the central nervous system--to serve the limbs and organs, for example. ... The pia mater (Latin: tender mother, itself a translation from Arabic) is the delicate innermost layer of the meninges - the membranes surrounding the brain and spinal cord. ... The meninges (singular meninx) are the system of membranes that envelop the central nervous system. ...


The axon of an α-MN connects with its extrafusal muscle fiber via a neuromuscular junction, a specialized type of chemical synapse that differs both in structure and function from the chemical synapses that connect neurons to each other. Both types of synapses rely on neurotransmitters to transduce the electrical signal into a chemical signal and back. But they differ in that synapses between neurons typically use glutamate or GABA, while the neuromuscular junction uses acetylcholine exclusively. 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. ... Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between a neuron and another cell. ... The word transduction has several meanings: In developmental psychology, transduction is reasoning from specific cases to specific cases, typically employed by children. ... Glutamate is the anion of glutamic acid. ... Chemical structure of GABA Gamma-aminobutyric acid (GABA) is a neurotransmitter in widely divergent species. ... The skeletal structure of acetylcholine The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. ...


Role in disease

Main article: Motor neuron disease
Poliomyelitis, caused by the poliovirus seen here, is associated with the selective loss of cells within the ventral horn of the spinal cord, where α-MNs are located.
Poliomyelitis, caused by the poliovirus seen here, is associated with the selective loss of cells within the ventral horn of the spinal cord, where α-MNs are located.

Injury to α-MNs is the commonest type of lower motor neuron lesion. Damage may be caused by trauma, ischemia, and infection, among others. In addition, certain diseases are associated with the selective loss of α-MNs. Motor neuron disease (MND) is a term used to cover a number of illnesses of the motor neurone; amyotrophic lateral sclerosis (ALS), progressive muscular atrophy (PMA), spinal muscular atrophy (SMA), progressive bulbar palsy (PBP), and primary lateral sclerosis (PLS) are all forms of MND. MND is the term used internationally... Pubtjyujgykkjkjj File links The following pages link to this file: Polio Rhinovirus Enterobacteria phage T2 HTDV Reoviridae Picornaviridae Human respiratory syncytial virus Papillomavirus Wikipedia:Stub and disambiguation message example Wikipedia:Template messages/Stubs Ebola Reston Wikipedia:Stub categories Vibrio vilnificus Virus cancer link Wikipedia:Template messages/All Enterovirus Wikipedia:Template... Pubtjyujgykkjkjj File links The following pages link to this file: Polio Rhinovirus Enterobacteria phage T2 HTDV Reoviridae Picornaviridae Human respiratory syncytial virus Papillomavirus Wikipedia:Stub and disambiguation message example Wikipedia:Template messages/Stubs Ebola Reston Wikipedia:Stub categories Vibrio vilnificus Virus cancer link Wikipedia:Template messages/All Enterovirus Wikipedia:Template... Poliomyelitis, often called polio or infantile paralysis, is a viral paralytic disease. ... Poliomyelitis (polio) is a viral paralytic disease. ... Cross-section through cervical spinal cord. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Trauma can represent: Physical trauma, an often serious and body-altering physical injury, such as the removal of a limb. ... In medicine, ischemia (Greek ισχαιμία, isch- is restriction, hema or haema is blood) is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. ... Infection is also the title of an episode of the television series Babylon 5, and the English title of the Japanese film Kansen. ...


For example, poliomyelitis is caused by a virus that specifically targets and kills motor neurons in the ventral horn of the spinal cord. Amyotropic lateral sclerosis likewise is associated with the selective loss of motor neurons. Poliomyelitis, often called polio or infantile paralysis, is a viral paralytic disease. ... Orders A virus is a submicroscopic particle that can infect the cells of a biological organism. ... Motor Neurone Disease (MND) is a term used to cover a number of illnesses of the motor neurone. ...


Paralysis is one of the most pronounced effects of damage to α-MNs. Because α-MNs provide the only voluntary innervation to extrafusal muscle fibers, losing α-MNs effectively severs the connection between the brainstem and spinal cord and the muscles they innervate. Without this connection, muscle control is impossible. In addition, muscle tone is reduced (flaccid paresis) with the loss of this connection and consequent interruption of the tonic stretch reflex. Interruption of other reflex circuits results in depressed reflexes (hyporeflexia). Paralysis is the complete loss of muscle function for one or more muscle groups. ... Extrafusal muscle fibers are served by axons of the alpha motor neurons. ... Muscle tone is the continuous and passive partial contraction of the muscles. ... A reflex action or reflex is a biological control system linking stimulus to response and mediated by a reflex arc. ...


Muscle weakness and atrophy are inevitable consequences of α-MN lesions as well. Because muscle size and strength are related to the extent of their use, denervated muscle is prone to atrophy. A secondary cause of muscle atrophy is that denervated muscles are no longer supplied with trophic factors from the α-MNs that innervate them. Atrophy is the partial or complete wasting away of a part of the body. ...


Alpha motor neuron lesions also result in abnormal EMG potentials (eg, fibrillation potentials) and fasciculations, the latter being spontaneous, involuntary muscle contractions. Electromyography (EMG) is a medical technique for measuring muscle response to nervous stimulation. ... A fasciculation is a small, local involuntary muscle contraction (twitching) visible under the skin arising from the spontaneous discharge of a bundle of skeletal muscle fibres. ...


Diseases that impair signaling between α-MNs and extrafusal muscle fibers have similar signs to those that occur with α-MN disease. For example, myasthenia gravis is an autoimmune disease that prevents signaling across the neuromuscular junction, which effectively results in muscle denervation. Myasthenia gravis (MG, Latin: grave muscle weakness) is a neuromuscular disease leading to fluctuating weakness and fatiguability. ... Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body. ... 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. ...


Development

Alpha motor neurons originate in the basal plate, the ventral portion of the embryonic neural tube. Sonic hedgehog (Shh), a ventralizing morphogen, is secreted by the notochord and other ventral structures (eg, the floor plate), establishing a gradient of high Shh in the basal plate, and low Shh in the alar plate. Under the influence of Shh and other factors, some neurons of the basal plate differentiate into α-MNs. Like other neurons, α-MNs send axonal projections to reach their target extrafusal muscle fibers via axon guidance, a process regulated in part by neurotrophic factors released by target muscle fibers. The neural tube is the embryonal structure that gives rise to the brain and spinal cord. ... Sonic hedgehog homolog (SHH) is one of five proteins in the vertebrate hedgehog (HH) family thus far described, the others being desert hedgehog (DHH), Indian hedgehog (IHH), echidna hedgehog (EHH) and tiggywinkle hedgehog (TwHH). ... A morphogen is a substance governing the pattern of tissue development and, in particular, the positions of the various specialized cell types within a tissue. ... The notochord is a flexible, rod-shaped body found in embryos of all chordates. ... Differentiation can mean the following: In biology: cellular differentiation; evolutionary differentiation; In mathematics: see: derivative In cosmogony: planetary differentiation Differentiation (geology); Differentiation (logic); Differentiation (marketing). ... An axon, or nerve fiber, is a long slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... Extrafusal muscle fibers are served by axons of the alpha motor neurons. ... Axon guidance (also called axon pathfinding) is a subfield of neural development concerning the process by which neurons send out axons to reach the correct targets. ... Neurotrophins are a family of molecules that encourage survival of nervous tissue. ...


Neurotrophic factors also ensure that each muscle fiber is innervated by the appropriate number of α-MNs. As with most types of neurons in the nervous system, α-MNs are more numerous in early development than in adulthood. Muscle fibers secrete a limited amount of neurotrophic factors capable of sustaining only a fraction of the α-MNs that initially project to the muscle fiber. Those α-MNs that do not receive sufficient neurotrophic factors will undergo apoptosis, a form of programmed cell death. The 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. ... A cell undergoing apoptosis. ... Programmed cell death (PCD) is the deliberate suicide of an unwanted cell in a multicellular organism. ...


In addition to receiving neurotrophic factors from muscles, α-MNs also secrete a number of trophic factors to support the muscle fibers they innervate. Reduced levels of trophic factors is one reason for muscle atrophy following an α-MN lesion.


Nomenclature

Like other motor neurons, α-MNs are named after the properties of their axons. Alpha motor neurons have Aα axons, which are large-caliber, heavily myelinated fibers that conduct action potentials rapidly. By contrast, gamma motor neurons have Aγ axons, which are slender, lightly myelinated fibers that conduct less rapidly. An axon, or nerve fiber, is a long slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... The word calibre (British English) or caliber (American English) designates the interior diameter of a tube or the exterior diameter of a wire or rod, also common for handguns. ... In neuroscience, myelin is an electrically insulating phospholipid layer that surrounds the axons of many neurons. ... A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ...


References

  • John A. Kiernan (2005). Barr's the Human Nervous System: An Anatomical Viewpoint, 8th edition, Hagerstwon, MD: Lippincott Williams & Wilkins. ISBN 0781751543.
  • Duane E. Haines (2004). Neuroanatomy: An Atlas of Structures, Sections, and Systems, 6th edition, Hagerstwon, MD: Lippincott Williams & Wilkins. ISBN 0781746779.

  Results from FactBites:
 
Somatic nervous system - Wikipedia, the free encyclopedia (273 words)
The upper motor neuron carries this stimulus down the corticospinal tract and synapses in the ventral horn of the spinal cord with the alpha motor neuron, a lower motor neuron.
The upper motor neuron releases acetylcholine from its axon terminal knobs and these are received by nicotinic receptors on the alpha motor neuron.
The alpha motor neurons cell body sends the stimulus down its axon via the ventral root of the spinal cord and proceeds to its neuromuscular junction of its skeletal muscle.
Lower motor neuron - Wikipedia, the free encyclopedia (150 words)
Alpha motor neurons (α-MNs) innervate extrafusal muscle fibers, the most numerous type of muscle fiber and the one most involved in contracting in a muscle.
Gamma motor neurons (γ-MNs) innervate intrafusal muscle fibers, which are involved with muscle spindles and the sense of body position.
Damage to lower motor neurons is indicated by abnormal EMG potentials, fasciculations, paralysis, weakening of muscles, and neurogenic atrophy of skeletal muscle.
  More results at FactBites »

 
 

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Persona
18th May 2010
What does this have to do w/ Costanzo Varolio?

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