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Topic: Alpha motor neuron

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	Somatic nervous system - Wikipedia, the free encyclopedia
		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.
	en.wikipedia.org /wiki/Somatic_nervous_system (273 words)

	Lower motor neuron - Wikipedia, the free encyclopedia
		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.
	en.wikipedia.org /wiki/Lower_motor_neuron (150 words)

	Upper Motor Neuron System Hypotonia
		Generalized hypotonia may be due to an upper motor neuron lesion, a lower motor neuron lesion, or a combination of upper and lower motor neuron lesions.
		Combined upper and lower motor lesions may occur with damage to lower motor neurons of the arms and the upper motor neurons of the legs in the lower cervical spinal cord (4).
		Upper motor neuron system hypotonia is not associated with any specific electromyographic, nerve conduction velocity, repetitive stimulation test, or muscle biopsy abnormalities unless there is simultaneous involvement of the alpha motor neurons and the muscle fibers (motor-sensory unit).
	www.pediatricneuro.com /alfonso/pg104.htm (282 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 be due to an upper motor neuron lesion at the (1) brain, (2) brainstem, (3) rostral cervical spinal cord, or (5) cerebellum.
		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)

	biological-cybernetics
		Extrapyramidal Tract: This is the ancillary spinal motor tract.
		The rate of discharge of the Renshaw cell is thus broadly proportional to the rate of discharge of the associated motor neuron, and the rate of discharge of the motor neuron is broadly inversely proportional to the rate of discharge of the Renshaw cell.
		The axons of these neurons - the alpha fibres - emerge via the ventral root of the spinal nerve, travel to the destination muscle, and cause contraction of the extrafusal muscle fibres (which form the bulk of the muscle).
	www.smithsrisca.demon.co.uk /biological-cybernetics.html (3991 words)

	Mod_6
		All primary afferent neurons are monosynaptically excitatory to the IML.
		Motor neurons must be actively inhibited to maintain viability in the absence of movement and to allow smoothness of movement when it does occur.
		The gamma motor neurons supply contractile proteins at the polar ends of the muscle spindle receptor and their contraction dictates the amount of distortion, preload, or gain of the spindle cell.
	www.dendrites.com /mod_6.html (5462 words)

	The Motor System
		Motor neurons in ventral portion of ventral horn ù responsible for extensor movement.
		Motor neurons in dorsolateral region of spinal cord ù innervate muscles in extremities.
		Thus activation of the gamma motor neuron prevents the muscle spindle from slackening during shortening of the extrafusal fibers i.e.
	www.bioweb.uncc.edu /humanphys/motor.htm (2329 words)

	Some notes on motor pathways
		A motor neuron is a cell in the anterior horn (or in a motor nucleus of a cranial nerve) whose axon supplies the contractile fibres in skeletal muscles.
		A lower motor neuron lesion (such as destruction of cell bodies or transection of axons in a ventral root or peripheral nerve) causes flaccid paralysis, loss of the stretch reflex, and considerable atrophy.
		An upper motor neuron lesion (such as transection of corticospinal and corticoreticular fibers in the internal capsule) causes spastic paralysis, with exaggerated stretch reflexes and the abnormal Babinski reflex (upgoing plantar reflex; down is normal.
	instruct.uwo.ca /anatomy/530/motor.htm (1103 words)

	Principles of Physiology
		All of the muscle fibers controlled by one alpha motor neuron are called a motor unit.
		Ib sensory fibers synapse in the ventral horn with numerous interneurons that are inhibitory to alpha motor neurons that supply the muscle.
		In the same manner the alpha motor neurons of flexor of one limb excite the extensor of the opposite limb which brings us to central pattern generators.
	www.sonoma.edu /users/h/hanesda/B497/bear13 (572 words)

	lec17 (Site not responding. Last check: 2007-10-23)
		- Gamma motor axons terminate on the polar region of the intrafusal fibres.
		Step 2b: Action potential is carried along the afferent fibre and results in release of neurotransmitter at the alpha motor neuron and an inhibitory interneuron synapse (Disynaptic pathway).
		Step 3b: The action of the Neurotransmitter is excitatory on the inhibitory interneuron that is between the primary afferent fibre and an alpha-motor neuron that innervates the antagonist muscle.
	www.sfu.ca /~ablaber/lec14.htm (964 words)

	Proprioception, Kinesthesia, and Motor Reflexes (Site not responding. Last check: 2007-10-23)
		Neurons of the vestibular nuclei project to the spinal cord, cerebellum, medulla and pons.
		With the consequent release of tension their firing rate is lowered both to the alpha motor neuron of the agonist and the inhibitor interneuron of the antagonist.
		Their output eventually influences motor behavior via the vestibulospinal and reticulospinal tracts of the ventromedial pathways.When the frontal lobes plan to initiate an action, intended movements are passed to the lateral zone of the cerebellum via the pontine nucleus.
	www.nanonline.org /nandistance/nanneuro2/modules/proprio/proprio.html (2018 words)

	Effectors
		The cell bodies of alpha motor neurons are located in lamina IX in the spinal cord (see picture at right) and in certain cranial nerve-related motor nuclei (see separate section on cranial nerves).
		One alpha motor neuron innervates from as few as 5-15 skeletal muscle fibers or up to as many as 150-200.
		A motor unit is defined as an alpha motor neuron and all of the extrafusal muscle fibers it innervates.
	www.sci.uidaho.edu /med532/effectors_module1.htm (278 words)

	eMedicine - Spinal Muscle Atrophy : Article Excerpt by: Jose A Herrera-Soto, MD (Site not responding. Last check: 2007-10-23)
		The characteristic muscle weakness occurs due to a progressive degeneration of the alpha motor neuron from anterior horn cells in the spinal cord.
		Pathophysiology: SMA is caused by a mutation in the survival motor neuron gene.
		This gene becomes active in the healthy mature fetus to stabilize the neuronal population.
	www.emedicine.com /orthoped/byname/spinal-muscle-atrophy.htm (617 words)

	Electromyography - EMG
		The functional unit of the muscle contraction is a motor unit, which is comprised of a single alpha motor neuron and all the fibers it enervates.
		The motor unit action potential is the spatio and temporal summation of the individual muscle action potentials for all the fibers of a single motor unit.
		Therefore, the EMG signal is the algebraic summation of the motor unit action potentials within the pick-up area of the electrode being used.
	www.digital-humans.org /EMG.htm (408 words)

	[No title]
		A motor neuron is a large multipolar cell found in the ventral horn of the spinal cord, with its axon ending of an effector organ.
		Tonic neck reflexes are changes in the extensor tone of the limbs in response to head movements and are mediated by receptors in the neck muscles and joints of the cervical vertebrae.
		This is an upper motor neuron lesion and results in spasticity, hyperreflexia, Babinski, clonus, and paresis or paralysis.
	www.kumc.edu /research/medicine/pharmacology/CAI/webCAI/anatomy/ua28.wbc (1071 words)

	Spinal Cord - Spasticity after spinal cord injury (Site not responding. Last check: 2007-10-23)
		In general, spasticity is classified as a symptom of the upper motor neuron syndrome, characterized by an exaggeration of the stretch reflex secondary to hyperexcitability of spinal reflexes.
		Upper motor neurons originate in the brain and brain stem and project to lower motor neurons within the brain stem and spinal cord.
		The lower motor neurons are of two types, both of which originate in the ventral horn of the spinal cord: (1) alpha motor neurons project to extrafusal skeletal fibers and (2) gamma motor neurons project to intrafusal muscle fibers within the muscle spindle.
	www.nature.com /sc/journal/v43/n10/full/3101757a.html (5728 words)

	[No title] (Site not responding. Last check: 2007-10-23)
		In general, gamma motor neurons increase the sensitivity of the spindles.
		When the gamma motor neuron is active, contractile elements, at either pole of the spindle, contract.
		Gamma motor neurons are often called dynamic fusimotor neurons because they increase the overall sensitivity of type Ia fibers (afferents) especially to dynamic stimuli.
	www.muhealth.org /~md2004/draft3/1-24reflex.doc (402 words)

	Motor Neuron Disease
		Motor neuron disease refers to selective loss of neurons which are either in the primary motor area of the cerebral cortex (so-called "upper motor neurons") or the alpha motor neurons located at each segment of the spinal cord, whose fibers make up nerves which go to muscles (so-called "lower motor neuron").
		There is no loss of sensory neurons, and many parts of the brain and spinal cord which are not strictly "motor" are unaffected.
		ALS (amyotrophic lateral sclerosis) is a combination of upper and lower motor neuron degeneration.
	www.medhelp.org /perl6/neuro/archive/5444.html (350 words)

	Dorlands Medical Dictionary
		alpha m.’s neurons of the anterior spinal cord that give rise to the alpha fibers which innervate the skeletal muscle fibers.
		a peripheral neuron whose cell body lies in the ventral gray columns of the spinal cord and whose termination is in a skeletal muscle.
		a neuron in the cerebral cortex that conducts impulses from the motor cortex to a motor nucleus of one of the cerebral nerves or to a ventral gray column of the spinal cord.
	www.mercksource.com /pp/us/cns/cns_hl_dorlands.jspzQzpgzEzzSzppdocszSzuszSzcommonzSzdorlandszSzdorlandzSzdmd_m_20zPzhtm (3360 words)

	3 types of muscles:
		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
		gamma motor neuron - efferent axon causes the intrafusal muscle fiber to contract, but contributes little force; serves to modify the sensitivity of the fiber’s afferent axon to force
		alpha motor neuron and gamma motor neurons activated
	home.epix.net /~tcannon1/physioweek4.htm (1018 words)

	Muscle Disease (Site not responding. Last check: 2007-10-23)
		As the function of muscle is specifically motor, the correlative factors for muscle disease relate to motor function or dysfunction.
		Motor dysfunction can originate either in a lower motor unit which includes the alpha motor neuron, its axon, neuromuscular junction and muscle fibers or in an upper motor neuron unit which includes the pyramidal cell in the cortex, its axon and connection to the lower motor neuron in the spinal cord.
		The big clinical distinction is that lower motor neuron unit disease causes weakness and hyporeflexia while upper motor unit disease cause weakness, spasticity and hyperreflexia.
	www.uottawa.ca /academic/med/hendelman/locrules/lr3.htm (222 words)

	Rehabilitation medicine: 3. Management of adult spasticity -- Satkunam 169 (11): 1173 -- Canadian Medical Association ...
		When a muscle is stretched, an impulse is generated in the muscle spindle and is transmitted via the sensory neuron to the grey matter of the spinal cord.
		Here the sensory neuron synapses with the motor neuron, and the transmitted impulse results in muscle contraction.
		Factors that play a role in suppressing hyperactivity of the final common pathway at the spinal cord level include nonreciprocal Ib inhibition (from golgi tendon organ receptors in tendons), presynaptic inhibition of the Ia terminal (at the axoaxonic synapse between 2 axons), reciprocal Ia inhibition by the inhibitory interneuron (inhibition of antagonistic muscles [see Fig.
	www.cmaj.ca /cgi/content/full/169/11/1173 (2529 words)

	Introduction to Neural Science, Spring 2002, Final Exam, Qs & As
		In neurons that cannot generate an action potential (nonspiking neurons), inhibition decreases the amount of neurotransmitter that is released by the neuron.
		Think about neurons in the optic nerve or in the dorsal columns of the spinal cord, which have the task of conveying information about the nature of the stimulus to the thalamus.
		Discuss the contribution of gamma motor neurons to the antigravity reflex.
	www.cns.nyu.edu /~sam/introns/introns02/exam3key (2449 words)

	Neuro course 2006 Spinal Motor Lecture (Site not responding. Last check: 2007-10-23)
		Spinal motor neuron cell bodies are labeled by injection of marker into the muscle (soleus vs gastrocnemius)
		Also (this is a different point) each motor neuron innervates only one type (white meat, dark meat) of muscle.
		In the ventral horn of the spinal cord, where are motor neurons controlling the hand relative to those controlling the shoulders?
	starklab.slu.edu /neuro/Motor.htm (653 words)

	Motor units (Site not responding. Last check: 2007-10-23)
		A muscle is composed of many motor units.
		Each muscle fiber within a motor unit is of the same fiber type.
		The fibers that make up a motor unit are not adjacent to one another, but they inhabit the same general region of the muscle.
	moon.ouhsc.edu /gsharp/namics/mu.htm (98 words)

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