FACTOID # 28: Austin, Texas has more people than Alaska.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
   
 
WHAT'S NEW
RELATED ARTICLES
People who viewed "Motoneuron" also viewed:
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Motoneuron

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. Groups Conodonta Hyperoartia Petromyzontidae (lampreys) Pteraspidomorphi (early jawless fish) Thelodonti Anaspida Cephalaspidomorphi (early jawless fish) Galeaspida Pituriaspida Osteostraci Gnathostomata (jawed vertebrates) Placodermi Chondrichthyes (cartilaginous fish) Acanthodii Osteichthyes (bony fish) Actinopterygii (ray-finned fish) Sarcopterygii (lobe-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Tetrapoda Amphibia Amniota Sauropsida/(Reptiles) Aves (Birds) Synapsida Mammalia... Efferent nerve fibers carry information away from the brain. ... Neurons (also spelled neurones or called nerve cells) are the primary cells of the nervous system. ... A top-down view of skeletal muscle A muscle fiber (American usage) or muscle fibre (British usage) (also technically known as a myocyte) is a single cell of a muscle. ... A top-down view of skeletal muscle Muscle is a contractile form of tissue. ... Contraction can mean: Contraction (childbirth), a contraction during childbirth; Contraction (linguistics), a new word formed from two or more individual words; Contraction (science), one that can occur to solid matter as it cools; Contraction mapping, in mathematics, a type of function on a metric space; Muscle contraction, one that occurs... A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ... Proprioception (from Latin proprius, meaning ones own and perception) is the sense of the position of parts of the body, relative to other neighbouring parts of the body. ...

Contents


Anatomy and physiology

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

Motoneurons of both the somatic and autonomic nervous system (ANS) originate in the ventral gray column of the spinal cord. Somatic fibers innervate skeletal muscle while autonomic fibers innervate cardiac muscle of the heart and smooth muscle of the visceral organs and glands. Sweating (also called perspiration or sometimes transpiration) is the loss of a watery fluid, consisting mainly of sodium chloride and urea in solution, that is secreted by the sweat glands in the skin of mammals. ... The arterial system The blood vessels are part of the circulatory system and function to transport blood throughout the body. ... 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. ... This article needs to be cleaned up to conform to a higher standard of quality. ... In zootomy, several terms are used to describe the location of organs and other structures in the body of bilateral animals. ... A gray column is one of the three somewhat ridge-shaped masses of gray matter in the spinal cord. ... The spinal cord is a part of the vertebrate nervous system that is enclosed in and protected by the vertebral column (it passes through the spinal canal). ... A top-down view of skeletal muscle Skeletal muscle is a type of striated muscle, attached to the skeleton. ... Cardiac muscle is a type of striated muscle found within the heart. ... The heart and lungs (from an older edition of Grays Anatomy) The heart (Latin cor) is a hollow, muscular organ that pumps blood through the blood vessels by repeated, rhythmic contractions. ... Smooth muscle is a type of non-striated muscle, found within the walls of hollow organs; such as blood vessels, bladders, uteri. ... In mammalian anatomy, the viscera are the internal organs of the body, in particular the stomach and intestines. ... A gland is an organ in an animals body that synthesizes a substance for release such as hormones, often into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland). ...


In the somatic nervous system, the pathway of a motoneuron from the spinal cord to the skeletal muscle fiber is composed of a single motoneuron. By contrast, the analogous pathway in the ANS is composed of two motoneurons that synapse in an autonomic ganglion. Motoneurons of the ANS are thus called preganglionic and postganglionic depending on their position relative to their ganglion. Sympathetic nervous system innervation, showing the sympathetic chain ganglia An autonomic ganglion is a collection of neuron cell bodies within the autonomic nervous system. ...


Motoneurons are further classified depending on the neurotransmitter they release. Those that release noradrenaline (norepinephrine) are called adrenergic, while those that release acetylcholine are dubbed cholinergic. All motoneurons are cholinergic except for most postganglionic fibers of the sympathetic nervous system, which are adrenergic. An exception is made for sympathetic postganglionic fibers that innervate sweat glands and certain blood vessels; these fibers are cholinergic. Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between a neuron and another cell. ... Norepinephrine, known as noradrenaline outside the USA, is a catecholamine and a phenethylamine with chemical formula C8H11NO3. ... Norepinephrine or noradrenaline is a catecholamine and a phenethylamine with chemical formula C8H11NO3. ... The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. ... Sweating (also called perspiration or sometimes transpiration) is the loss of a watery fluid, consisting mainly of sodium chloride and urea in solution, that is secreted by the sweat glands in the skin of mammals. ... The arterial system The blood vessels are part of the circulatory system and function to transport blood throughout the body. ...


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. 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. This is why muscle relaxants work by acting on the nerves that innervate muscles (by decreasing their electrophysiological activity) or on cholinergic neuromuscular junctions, rather than on the muscles themselves. 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. ... Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between a neuron and another cell. ... Receptor may refer to: In telecommunication, a receiver. ... 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. ... Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between a neuron and another cell. ... In medicine, a muscle relaxant is a drug that causes skeletal muscle contraction to cease. ... A nerve is an enclosed, cable-like bundle of nerve fibers or axons, which includes the glia that ensheath the axons in myelin. ... This article needs to be cleaned up to conform to a higher standard of quality. ... 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

There are two types of somatic motoneurons: 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.) Alpha motoneurons innervate extrafusal muscle fibers (typically referred to simply as muscle fibers) located throughout the muscle. Gamma motoneurons innervate intrafusal muscle fibers found within the muscle spindle. A diagram showing the CNS. The central nervous system (CNS) represents the largest part of the nervous system. ... The peripheral nervous system or PNS, is part of the nervous system,and I have no clue what it does. ... extrafusal muscle fibers - served by axons of the alpha motor neurons (serve multiple muscle fibers); contraction of these muscles provides movement - extrafusal muscle fibers and associated alpha motor neurons are called a motor unit ... Intrafusal fibers are fibers within the muscle spindle. ... A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ...


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. Muscle tone is the continuous and passive partial contraction of the muscles. ... Sensory neurons are nerve cells within the nervous system responsible for converting external stimuli from the organisms environment into internal electrical impulses. ... A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ...


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 called 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. ... Motor neurone 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...

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:
 
Motoneuron - TheBestLinks.com - Central nervous system, Muscle, Neuron, Neurotransmitter, ... (613 words)
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.
Upon adequate stimulation, the motoneuron releases a flood of neurotransmitters that bind to postsynaptic receptors and triggers a response in the muscle fiber.
The motoneuron and all of the muscle fibers to which it connects is called a motor unit.
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m