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Topic: Motor unit

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	Motor unit -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-11-06)
		A motor unit is a single (A neuron conducting impulses outwards from the brain or spinal cord) motor neuron and the corresponding muscle fibers it innervates; groups of motor units work together, as a single (One of the contractile organs of the body) muscle.
		In general, the number of (An elongated contractile cell that forms the muscles of the body) muscle fibers innervated by a motor unit is a function of a muscle's need for refined motion.
		Muscles requiring more refined motion are innervated by motor units that (The junction between two neurons (axon-to-dendrite) or between a neuron and a muscle) synapse with fewer muscle fibers.
	www.absoluteastronomy.com /encyclopedia/m/mo/motor_unit.htm (183 words)

	EMG & Nerve Conductions \| Electronic EMG Manual : The Motor Unit
		The motor unit action potential is the electrical field generated by muscle fibers belonging to one motor unit as recorded by the tip of the nearby needle electrode.
		The number of phases a motor unit contains depends largely on the synchrony of depolarization of its muscle fibers and can be affected either by nerve disease causing differential slowing in impulse conduction, or muscle disease where the conduction characteristics of the muscle fibers themselves have changed.
		Motor unit potentials' duration is measured with an amplification setting of 100-200 µv/division, and their amplitude at settings of 500 µv - 2000 µv/division, depending on the size of the motor unit under study.
	www.teleemg.com /new/jbr110.htm (1029 words)

	eMedicine - Motor Unit Recruitment in EMG : Article by Friedhelm Sandbrink, MD (Site not responding. Last check: 2007-11-06)
		This orderly recruitment of sequentially larger motor units is referred to as the "Henneman size principle." Recording from the ventral rootlets in cats and measuring the amplitudes of motor axon spikes, Henneman et al concluded that motor axon diameter, conduction velocity and, by further inference, motor neuron cell size all increase with functional threshold.
		The orderly recruitment of successive motor units may be described as a rough approximation by the "rule of fives." Motor units begin firing at stable rates at 5 Hz.
		The interference pattern is dependent on the shape of the individual motor unit potentials (eg, amplitude, duration, polyphasia), the firing rates, and the number of active units.
	www.emedicine.com /neuro/topic332.htm (3783 words)

	Motor neurone disease Medical Guide
		Motor units consist of a single motor neurone and all of the muscle fibres it supplies through its extensive branching.
		Disorders of motor units can affect the muscles and / or the neuro-muscular junctions, in which case they are called myopathies; or the motor neurones, in which case they are called neuropathies.
		Motor neurone diseases are now regarded as multisystem diseases in which the motor neurones tend to be affected earliest and most severely, however other parts of the nervous system may also be affected.
	www.medicalguidesonline.com /article.asp?id=173 (2166 words)

	* Motor Unit - (Fitness): Definition (Site not responding. Last check: 2007-11-06)
		Motor units are recruited in order according to their size as voluntary contraction increases from zero to maximal force (100% maximum contraction).
		The functional connection between the brain and the muscle is termed the "motor unit" (1).
		A motor unit consists of a motor neuron and the associated muscle fibers it innervates (2)...
	www.bestknows.com /fitness/motor_unit.html (132 words)

	Simulation of motor unit recruitment and microvascular unit perfusion: spatial considerations -- Fuglevand and Segal 83 ...
		Motor unit territories were modeled to be square, with motor unit fibers randomly distributed throughout the territory.
		Normally, motor units are recruited in an orderly sequence, progressing from small to large force units (25, 45, 61).
		unit) was representative of a motor unit in the upper one-third
	www.jap.org /cgi/content/full/83/4/1223 (7767 words)

	Motor Development Tidbits (Site not responding. Last check: 2007-11-06)
		Motor units are fired more frequently (rate coding) with greater workloads greater than 50% of of maximum force (Kulkulka and Clamann 1981).
		In these muscles, motor units are recruited in order according to their size as voluntary contraction increases from zero to maximal force (100% maximum contraction).
		Motor units are fired faster during eccentric contraction and slower during concentric and isometric contractions.
	www.exrx.net /ExInfo/MotorDevelopment.html (982 words)

	Effects of Aging on Motor-Unit Control Properties -- Erim et al. 82 (5): 2081 -- Journal of Neurophysiology
		motor units of all thresholds yielded 18.33 ± 2.76 pps for the
		The total number of motor units in each group are 20% of MVC (A): 69 from young, 68 from elderly; 50% of MVC (B): 43 from young and 51 from elderly.
		In the elderly, the systematic decrease in firing rates of motor units during a sustained contraction was not observed consistently.
	jn.physiology.org /cgi/content/full/82/5/2081 (7072 words)

	Lincolnshire Post-Polio Library [Original Research - Electrophysiology and Electrodiagnosis of the Post-Polio Motor ...
		Electrical excitation of a motor neuron in the central nervous system is followed by conduction of an impulse in the axon and its terminal branches, synaptic transmission at the neuromuscular junction mediated by the neurotransmitter acetylcholine, and depolarization and contraction of the muscle fibers it innervates.
		Motor neurons innervating Type II fibers are characterized by a higher threshold for activation, higher axonal conduction velocity, and a higher firing rate than motor neurons innervating Type I fibers.
		It is possible that a combination of factors, including the degree of motor unit deterioration, reserve present in the muscle affected, the functional importance of the muscle involved, and the general activity level of the patient will determine whether or not new symptoms are perceived by the patient.
	www.ott.zynet.co.uk /polio/lincolnshire/library/trojan/electrophysiology.html (5591 words)

	The Motor-Sensory Unit System
		Alpha motor neuron disease refers to disorders that affect the alpha motor neuron located in the anterior horn of the spinal cord, in the motor nucleus of the cranial nerves, or at both locations.
		Generalized hypotonia may result from damage to lower motor neurons of the arms and the upper motor neurons of the legs in the lower cervical spine area (4).
		Generalized hypotonia may be due to lower motor neuron lesions at the: (6) alpha motor neuron; (7) nerve; (8) presynaptic myoneural junction; (9) postsynaptic myoneural junction; and (10) muscle.
	pediatricneuro.com /alfonso/pg130.htm (319 words)

	Motor Unit Firing Patterns in Hemiplegia (Site not responding. Last check: 2007-11-06)
		EMG signals are decomposed into their constituent parts, the discharge patterns of individual motor unit (MU) action potential trains identified, and the control properties of groups of concurrently active motor units compared between subject groups and across task conditions.
		Motor unit discharge rates observed in the isometric 40% MVC contractions are significantly increased in hemiparetic persons (Controls mn=12.04 pps, CVA-I mn=12.63 pps (paretic), mn=11.73 pps (non-paretic), CVA-II mn=13.98 pps (paretic), mn=20.94 pps (non-paretic) p <.0001).
		In dynamic contractions transitional motor unit activity, including substitution of motor units across repeated cycles of locomotor activity and motor units which fire only at the transitions between static and dynamic force regulation has been observed.
	guide.stanford.edu /Projects/2kprojects/stroke13.html (435 words)

	Reduced Endplate Currents Underlie Motor Unit Dysfunction in Canine Motor Neuron Disease -- Rich et al. 88 (6): 3293 -- ...
		Tetanic failure is quantified by the taking the difference between peak motor unit force and force present at the end of the motor neuron tetanic stimulus train, expressed as a fraction of the peak force (see Pinter et al.
		A: motor unit failure in a 144-day HCSMA homozygote was nearly complete as indicated by the presence of only the first and second electromyographic (EMG) responses to the 60 pulse, 150 Hz train (top signal, indicated by arrows) and negligible force production (lower signal).
		The properties of motor units in a fast and a slow twitch muscle during post-natal development in the kitten.
	jn.physiology.org /cgi/content/full/88/6/3293 (8033 words)

	Plasticity in Respiratory Motor Control: Invited Review: Mechanisms underlying motor unit plasticity in the respiratory ...
		Triple-labeled confocal images of diaphragm muscle neuromuscular junctions (axon terminal shown in red, motor end-plate in green, and MHC fiber type in blue) were used to determine the morphology of pre- and postsynaptic elements.
		and remodeling motor units (8, 21, 45, 68, 113).
		Evidence that brain-derived neurotrophic factor is a trophic factor for motor neurons in vivo.
	jap.physiology.org /cgi/content/full/94/3/1230 (5950 words)

	Tetrodotoxin prevents motor unit enlargement after partial denervation in rat hindlimb muscles -- Tam et al. 543 (2): ...
		Motor unit force is the product of innervation ratio (IR, the number of muscle fibres innervated by one motoneurone), muscle fibre CSA and specific force (force per unit area of muscle fibre).
		Motor unit twitch force of each single MU in each experimental muscle was corrected for changes in CSA by multiplying the recorded MU twitch force by the ratio of the mean muscle fibre CSA of all contralateral control muscles to that of all experimental muscles which belonged to the same experimental condition.
		ANOVA was also used to determine differences between the mean values of the motor unit twitch forces.
	jp.physoc.org /cgi/content/full/543/2/655 (4716 words)

	eMedicine - EMG Evaluation of the Motor Unit: The Electrophysiologic Biopsy : Article by Paul E Barkhaus, MD (Site not responding. Last check: 2007-11-06)
		The motor unit (MU) is a part of the neuromuscular system that contains an anterior horn cell, its axon, and all of the muscle fibers (MFs) that it innervates, including the axon's specialized point of connection to the MFs, the neuromuscular junction.
		Studies counting motor axons in anterior roots support the concept of MN loss, although "dying back" of motor axons cannot be excluded.
		EMG evaluation of the motor unit: the electrophysiologic biopsy.
	www.emedicine.com /neuro/topic610.htm (12786 words)

	Neuromuscular Junction/Motor Unit
		The motor unit includes a motor neuron and the muscle fibers it innervates.
		Acetylcholine is the neurotransmitter between the motor neuron and the muscle cell, and the muscle cell has nicotinic receptors.
		Motor units are recruited from weakest to strongest.
	sun.science.wayne.edu /~bio669/Neuromus.html (108 words)

	MOTOR-UNIT ORDERLY RECRUITMENT TELEOLOGICALLY EXPLAINED
		Muscle force gradation occurs through varying the number of active motor units and the rate at which the active motor units generate action potentials.
		As the force exerted by a muscle increases, new motor units are recruited and remain active until the force declines.
		This happens in a set sequence with slow-contracting, fatigue-resistant motor units being recruited first and fast-contracting, fatigue-sensitive motor units being recruited last.
	www.utc.fr /esb/esb98/abs_htm/469.html (356 words)

	The educational encyclopedia, muscular system, muscles, anatomy (Site not responding. Last check: 2007-11-06)
		Motor control systems a motor neurone and all the muscle fibres it innervates are termed a motor unit.
		When a motor neurone fires it causes all of the fibres in the motor unit to contract
		Muscle twitch a muscle twitch is an activation of a muscle fiber by a single firing of a motor neuron,
	users.pandora.be /educypedia/education/muscles.htm (525 words)

	Andrew Fuglevand - Arizona Research Laboratories Division of Neurobiology
		Our investigations evaluate interactions among various elements of the motor system, including skeletal muscle, somatosensory afferents, spinal cord, and brain.
		2004 Jun. Distribution of motor unit force in human extensor digitorum assessed by spike-triggered averaging and intraneural microstimulation.
		2004 Dec. Role of across-muscle motor unit synchrony for the coordination of forces.
	www.neurobio.arizona.edu /faculty/fuglevand/index.php (150 words)

	Motor unit - Wikipedia, the free encyclopedia
		A motor unit is a single motor neuron and the corresponding muscle fibers it innervates; groups of motor units work together, as a single muscle.
		The number of muscle fibers within each unit can vary: thigh muscles can have a thousand fibers in each unit, eye muscles might have ten.
		This page was last modified 19:52, 7 April 2005.
	en.wikipedia.org /wiki/Motor_unit (124 words)

	Example: Motor Unit (Site not responding. Last check: 2007-11-06)
		The amount of force generated in an anatomic muscle for a given task is dependent on how many motor units in it are "recruited" into use.
		In vertebrates (but not invertebrates) there is one motor end plate per myofiber and there is one axon which controls a group of motor end plates.
		Eventually, if all the motor units are in use and there is no reserve of rested and ready ones, the muscle shows complete fatigue and force generation has to be halted.
	education.vetmed.vt.edu /Curriculum/VM8054/Labs/Lab10/Examples/exmtruni.htm (241 words)

	UA Physiology: Andrew Fuglevand
		The broad goal of the work carried out in our laboratory is to understand how the mammalian nervous system controls the action of skeletal muscles to produce coordinated movements.
		We use a variety of experimental approaches, including computer modeling and simulation, single motor unit recording, and microneurographic methods to record and stimulate single sensory and motor axons.
		Our experiments address a range of topics from those related to how individual neurons integrate synaptic information to those associated with the development of new methods to restore movement and sensation in paralyzed individuals.
	www.physiology.arizona.edu /people/person.php?id=100 (294 words)

	Simulation of motor unit recruitment and microvascular unit perfusion: spatial considerations -- Fuglevand and Segal 83 ...
		Simulation of motor unit recruitment and microvascular unit perfusion: spatial considerations -- Fuglevand and Segal 83 (4): 1223 -- Journal of Applied Physiology
		Simulation of motor unit recruitment and microvascular unit perfusion: spatial
		Effect of motor unit recruitment on functional vasodilatation in hamster retractor muscle
	www.jap.org /cgi/content/abstract/83/4/1223 (750 words)

	Reduced Endplate Currents Underlie Motor Unit Dysfunction in Canine Motor Neuron Disease -- Rich et al. 88 (6): 3293 -- ...
		Reduced Endplate Currents Underlie Motor Unit Dysfunction in Canine Motor Neuron Disease.
		Hereditary canine spinal muscular atrophy (HCSMA) is an autosomal dominant degenerative disorder of motor neurons.
		units exhibited little or no evidence of axonal swellings.
	jn.physiology.org /cgi/content/abstract/88/6/3293 (575 words)

	kauai.ca - motor court (Site not responding. Last check: 2007-11-06)
		Wall Street rallied to finish moderately higher Monday as nervous investors got some reassurance from General Motors...
		BERRYVILLE - Johnny Fay Armer, 21, of Alpena, was sentenced to four years of supervised probation when he pleaded guilty to possession of methamphetamine and drug paraphernalia during county criminal court action Monday m...
		By Guardian Reporter TWO Civic United Front (CUF) leaders were yesterday brought before the Kisutu Resident Magistrate Court to answer criminal charges of assaulting and injuring journalists and also leading and taking pa...
	kauai.ca /motor-court/reference/search (228 words)

	CNN.com - Hyundai Motor unit raided - Nov. 26, 2003
		South Korean prosecutors have raided a leasing and lending unit of the country's top carmaker, Hyundai Motor, a spokesman for the affiliate told Reuters.
		A number of investigations are underway over suspected links between the country's family-run conglomerates and politicians and bureaucrats during last December's presidential election.
		Hyundai Motor shares are down 2.3 percent to 43,950 won Thursday afternoon, underperforming a 0.33 percent fall in the broader market.
	cnn.com /2003/BUSINESS/11/26/korea.hyundai.reut (189 words)

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