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{{Short description|Motor response evoked by electrical stimulation of a nerve}}
{{Short description|Motor response evoked by electrical stimulation of a nerve}}
{{about|the term as it applies to neuroscience|the type of electronic wavefunction in atomic physics|atomic orbital}}
{{about|the term as it applies to neuroscience|the type of electronic wavefunction in atomic physics|atomic orbital}}
In [[neuroscience]], an '''F wave''' is one of several motor responses which may follow the [[Muscle contraction|direct motor response (M)]] evoked by electrical stimulation of peripheral motor or mixed (sensory and motor) nerves.<ref name=":0">{{Cite book|title=Neuromuscular function and disease : basic, clinical, and electrodiagnostic aspects|date=2002|publisher=Saunders|others=Brown, William F. (William Frederick), 1939-, Bolton, Charles Francis, 1932-, Aminoff, Michael J. (Michael Jeffrey)|isbn=0-7216-8922-1|edition=1st|location=Philadelphia|oclc=46873002}}</ref> F-waves are the second of two late [[voltage]] changes observed after stimulation is applied to the skin surface above the [[Anatomical terms of location#Proximal and distal|distal]] region of a [[nerve]], in addition to the [[H-reflex]] (Hoffman's Reflex) which is a muscle reaction in response to electrical stimulation of innervating sensory fibers.<ref name=":1">{{Cite book|last1=Smith|first1=M|title=Oxford Textbook of Neurocritical Care|last2=Kofke|first2=WA|last3=Citerio|first3=G|publisher=Oxford University Press|year=2016|pages=175}}</ref><ref name=":2">{{Cite book|last1=Jerath|first1=Nivedita|last2=Kimura|first2=Jun|title=Clinical Neurophysiology: Basis and Technical Aspects |chapter=F wave, A wave, H reflex, and blink reflex |date=2019|series=Handbook of Clinical Neurology|volume=160|pages=225–239|doi=10.1016/B978-0-444-64032-1.00015-1|issn=0072-9752|pmid=31277850|isbn=9780444640321|s2cid=195813560}}</ref> Traversal of F-waves along the entire length of peripheral nerves between the [[spinal cord]] and muscle, allows for assessment of motor nerve conduction between distal stimulation sites in the arm and leg, and related motoneurons (MN's) in the cervical and lumbosacral cord.<ref name=":3">{{Cite journal|last=Fisher|first=Morris A.|date=2007-02-02|title=F-waves--physiology and clinical uses|journal=TheScientificWorldJournal|volume=7|pages=144–160|doi=10.1100/tsw.2007.49|issn=1537-744X|pmc=5901048|pmid=17334607 |doi-access=free }}</ref> F-waves are able to assess both [[Afferent nerve fiber|afferent]] and [[Efferent nerve fiber|efferent]] loops of the alpha motor neuron in its entirety.<ref name=":4">{{Cite book|last=Katirji, Bashar.|title=Electromyography in clinical practice : a case study approach|date=2007|publisher=Mosby Elsevier|isbn=978-0-323-07034-8|edition=2nd|location=Philadelphia|oclc=324995633}}</ref> As such, various properties of F-wave motor nerve conduction are analyzed in [[Nerve conduction study|nerve conduction studies (NCS)]],<ref>{{Cite journal|last1=Mallik|first1=A.|last2=Weir|first2=A. I.|date=2005|title=Nerve conduction studies: essentials and pitfalls in practice|journal=Journal of Neurology, Neurosurgery, and Psychiatry|volume=76|issue=Suppl 2 |pages=ii23–31|doi=10.1136/jnnp.2005.069138|issn=0022-3050|pmc=1765692|pmid=15961865}}</ref> and often used to assess [[Polyneuropathy|polyneuropathies]], resulting from states of neuronal demyelination and loss of peripheral axonal integrity.<ref name=":0" /><ref name=":5">{{Cite journal|last=Fisher|first=Morris A.|date=1992|title=AAEM minimonograph #13: H reflexes and F waves: Physiology and clinical indications|journal=Muscle & Nerve|language=en|volume=15|issue=11|pages=1223–1233|doi=10.1002/mus.880151102|pmid=1488060|s2cid=6174526|issn=1097-4598}}</ref><ref>{{Cite journal|last1=Lachman|first1=T|last2=Shahani|first2=B T|last3=Young|first3=R R|date=1980|title=Late responses as aids to diagnosis in peripheral neuropathy.|journal=Journal of Neurology, Neurosurgery, and Psychiatry|volume=43|issue=2|pages=156–162|issn=0022-3050|pmid=6244369|pmc=490491|doi=10.1136/jnnp.43.2.156}}</ref>
In [[neuroscience]], an '''F wave''' is one of several motor responses which may follow the [[Muscle contraction|direct motor response (M)]] evoked by electrical stimulation of peripheral motor or mixed (sensory and motor) nerves.<ref name=":0">{{Cite book|title=Neuromuscular function and disease: basic, clinical, and electrodiagnostic aspects|date=2002|publisher=Saunders|others=Brown, William F. (William Frederick), 1939-, Bolton, Charles Francis, 1932-, Aminoff, Michael J. (Michael Jeffrey)|isbn=0-7216-8922-1|edition=1st|location=Philadelphia|oclc=46873002}}</ref> F-waves are the second of two late [[voltage]] changes observed after stimulation is applied to the skin surface above the [[Anatomical terms of location#Proximal and distal|distal]] region of a [[nerve]], in addition to the [[H-reflex]] (Hoffman's Reflex) which is a muscle reaction in response to electrical stimulation of innervating sensory fibers.<ref name=":1">{{Cite book|last1=Smith|first1=M|title=Oxford Textbook of Neurocritical Care|last2=Kofke|first2=WA|last3=Citerio|first3=G|publisher=Oxford University Press|year=2016|page=175}}</ref><ref name=":2">{{Cite book|last1=Jerath|first1=Nivedita|last2=Kimura|first2=Jun|title=Clinical Neurophysiology: Basis and Technical Aspects |chapter=F wave, A wave, H reflex, and blink reflex |date=2019|series=Handbook of Clinical Neurology|volume=160|pages=225–239|doi=10.1016/B978-0-444-64032-1.00015-1|issn=0072-9752|pmid=31277850|isbn=978-0-444-64032-1|s2cid=195813560}}</ref> Traversal of F-waves along the entire length of peripheral nerves between the [[spinal cord]] and muscle, allows for assessment of motor nerve conduction between distal stimulation sites in the arm and leg, and related motoneurons (MN's) in the cervical and lumbosacral cord.<ref name=":3">{{Cite journal|last=Fisher|first=Morris A.|date=2007-02-02|title=F-waves--physiology and clinical uses|journal=TheScientificWorldJournal|volume=7|pages=144–160|doi=10.1100/tsw.2007.49|issn=1537-744X|pmc=5901048|pmid=17334607 |doi-access=free }}</ref> F-waves are able to assess both [[Afferent nerve fiber|afferent]] and [[Efferent nerve fiber|efferent]] loops of the alpha motor neuron in its entirety.<ref name=":4">{{Cite book|last=Katirji, Bashar.|title=Electromyography in clinical practice: a case study approach|date=2007|publisher=Mosby Elsevier|isbn=978-0-323-07034-8|edition=2nd|location=Philadelphia|oclc=324995633}}</ref> As such, various properties of F-wave motor nerve conduction are analyzed in [[Nerve conduction study|nerve conduction studies (NCS)]],<ref>{{Cite journal|last1=Mallik|first1=A.|last2=Weir|first2=A. I.|date=2005|title=Nerve conduction studies: essentials and pitfalls in practice|journal=Journal of Neurology, Neurosurgery, and Psychiatry|volume=76|issue=Suppl 2 |pages=ii23–31|doi=10.1136/jnnp.2005.069138|issn=0022-3050|pmc=1765692|pmid=15961865}}</ref> and often used to assess [[Polyneuropathy|polyneuropathies]], resulting from states of neuronal demyelination and loss of peripheral axonal integrity.<ref name=":0" /><ref name=":5">{{Cite journal|last=Fisher|first=Morris A.|date=1992|title=AAEM minimonograph #13: H reflexes and F waves: Physiology and clinical indications|journal=Muscle & Nerve|language=en|volume=15|issue=11|pages=1223–1233|doi=10.1002/mus.880151102|pmid=1488060|s2cid=6174526|issn=1097-4598}}</ref><ref>{{Cite journal|last1=Lachman|first1=T|last2=Shahani|first2=B T|last3=Young|first3=R R|date=1980|title=Late responses as aids to diagnosis in peripheral neuropathy.|journal=Journal of Neurology, Neurosurgery, and Psychiatry|volume=43|issue=2|pages=156–162|issn=0022-3050|pmid=6244369|pmc=490491|doi=10.1136/jnnp.43.2.156}}</ref>


With respect to its nomenclature, the F-wave is so named as it was initially studied in the smaller muscles of the foot.<ref>{{Cite journal|last1=Magladery|first1=J. W.|last2=McDOUGAL|first2=D. B.|date=1950|title=Electrophysiological studies of nerve and reflex activity in normal man. I. Identification of certain reflexes in the electromyogram and the conduction velocity of peripheral nerve fibers|journal=Bulletin of the Johns Hopkins Hospital|volume=86|issue=5|pages=265–290|issn=0097-1383|pmid=15414383}}</ref> The observation of F-waves in the same [[Motor unit|motor units (MU)]] as those present in the direct motor response (M),<ref>{{Cite journal|last1=Wulff|first1=C. H.|last2=Gilliatt|first2=R. W.|date=1979|title=F waves in patients with hand wasting caused by a cervical rib and band|journal=Muscle & Nerve|volume=2|issue=6|pages=452–457|doi=10.1002/mus.880020606|issn=0148-639X|pmid=514311|s2cid=2423723}}</ref> along with the presence of F-waves in deafferented animal and human models,<ref name=":6">{{Cite journal|last1=Fox|first1=J E|last2=Hitchcock|first2=E R|date=1987|title=F wave size as a monitor of motor neuron excitability: the effect of deafferentation.|journal=Journal of Neurology, Neurosurgery, and Psychiatry|volume=50|issue=4|pages=453–459|issn=0022-3050|pmc=1031882|pmid=3585357|doi=10.1136/jnnp.50.4.453}}</ref> indicates that F-waves require direct activation of motor axons to be elicited,<ref>{{Cite book|last=Trontelj|first=JV|title=A study of the F response by single fiber electromyography, in Desmedt JE (ed): New Developments in Electromyography and Clinical Neurophysiology|publisher=Karger|year=1973|location=Basel|pages=318–322}}</ref> and do not involve conduction along afferent sensory nerves. Thus, the F-wave is considered a wave, as opposed to a reflex.
With respect to its nomenclature, the F-wave is so named as it was initially studied in the smaller muscles of the foot.<ref>{{Cite journal|last1=Magladery|first1=J. W.|last2=McDOUGAL|first2=D. B.|date=1950|title=Electrophysiological studies of nerve and reflex activity in normal man. I. Identification of certain reflexes in the electromyogram and the conduction velocity of peripheral nerve fibers|journal=Bulletin of the Johns Hopkins Hospital|volume=86|issue=5|pages=265–290|issn=0097-1383|pmid=15414383}}</ref> The observation of F-waves in the same [[Motor unit|motor units (MU)]] as those present in the direct motor response (M),<ref>{{Cite journal|last1=Wulff|first1=C. H.|last2=Gilliatt|first2=R. W.|date=1979|title=F waves in patients with hand wasting caused by a cervical rib and band|journal=Muscle & Nerve|volume=2|issue=6|pages=452–457|doi=10.1002/mus.880020606|issn=0148-639X|pmid=514311|s2cid=2423723}}</ref> along with the presence of F-waves in deafferented animal and human models,<ref name=":6">{{Cite journal|last1=Fox|first1=J E|last2=Hitchcock|first2=E R|date=1987|title=F wave size as a monitor of motor neuron excitability: the effect of deafferentation.|journal=Journal of Neurology, Neurosurgery, and Psychiatry|volume=50|issue=4|pages=453–459|issn=0022-3050|pmc=1031882|pmid=3585357|doi=10.1136/jnnp.50.4.453}}</ref> indicates that F-waves require direct activation of motor axons to be elicited,<ref>{{Cite book|last=Trontelj|first=JV|title=A study of the F response by single fiber electromyography, in Desmedt JE (ed): New Developments in Electromyography and Clinical Neurophysiology|publisher=Karger|year=1973|location=Basel|pages=318–322}}</ref> and do not involve conduction along afferent sensory nerves. Thus, the F-wave is considered a wave, as opposed to a reflex.


== Physiology ==
== Physiology ==
F-waves are evoked by strong electrical stimuli (supramaximal) applied to the skin surface above the distal portion of a nerve.<ref name=":2" /> This impulse travels both in [[orthodromic]] fashion (towards the [[muscle fibers]]) and [[antidromic]] fashion (towards the cell body in the spinal cord) along the [[alpha motor neuron]].<ref name=":3" /><ref name=":5" /><ref name=":8"/><ref>{{Cite journal|last1=Sathya|first1=G. R.|last2=Krishnamurthy|first2=N.|last3=Veliath|first3=Susheela|last4=Arulneyam|first4=Jayanthi|last5=Venkatachalam|first5=J.|date=2017|title=F wave index: A diagnostic tool for peripheral neuropathy|journal=The Indian Journal of Medical Research|volume=145|issue=3|pages=353–357|doi=10.4103/ijmr.IJMR_1087_14|issn=0971-5916|pmc=5555064|pmid=28749398|doi-access=free}}</ref> As the orthodromic impulse reaches innervated muscle fibers, a strong direct motor response (M) is evoked in these muscle fibers, resulting in a primary [[Compound muscle action potential|compound muscle action potential (CMAP)]].<ref name=":2" /><ref name=":5" /> As the antidromic impulse reaches the [[Soma (biology)|cell bodies]] within the [[Anterior horn of spinal cord|anterior horn]] of the motor neuron pool by retrograde transmission, a select portion of these alpha motor neurons, (roughly 5-10% of available motor neurons), 'backfire' or rebound.<ref name=":1" /><ref name=":2" /><ref name=":3" /><ref name=":4" /> This antidromic 'backfiring' elicits an orthodromic impulse that follows back down the alpha motor neuron, towards innervated muscle fibers. Conventionally, axonal segments of motor neurons previously depolarized by preceding antidromic impulses enter a [[Hyperpolarization (biology)|hyperpolarized]] state, disallowing the travel of impulses along them.<ref name=":7">{{Cite book|last=Kimura|first=Jun|title=Clinical Neurophysiology of Motor Neuron Diseases|chapter=Peripheral nerve conduction studies and neuromuscular junction testing|date=2004-01-01|chapter-url=http://www.sciencedirect.com/science/article/pii/S1567423104040122|series=Handbook of Clinical Neurophysiology |volume=4|pages=241–270|editor-last=Eisen|editor-first=Andrew|publisher=Elsevier|language=en|access-date=2020-02-26|doi=10.1016/S1567-4231(04)04012-2|isbn=9780444513595}}</ref> However, these same axonal segments remains excitable or relatively depolarized for a sufficient period of time, allowing for rapid antidromic backfiring, and thus the continuation of the orthodromic impulse towards innervated muscle fibers.<ref name=":7" /><ref name=":8">{{Cite journal|last1=Panayiotopoulos|first1=C. P.|last2=Chroni|first2=E.|date=1996|title=F-waves in clinical neurophysiology: a review, methodological issues and overall value in peripheral neuropathies|journal=Electroencephalography and Clinical Neurophysiology|volume=101|issue=5|pages=365–374|issn=0013-4694|pmid=8913188}}</ref> This successive orthodromic stimulus then evokes a smaller population of muscle fibers, resulting in a smaller CMAP known as an F-wave.<ref name=":2" />
F-waves are evoked by strong electrical stimuli (supramaximal) applied to the skin surface above the distal portion of a nerve.<ref name=":2" /> This impulse travels both in [[orthodromic]] fashion (towards the [[muscle fibers]]) and [[antidromic]] fashion (towards the cell body in the spinal cord) along the [[alpha motor neuron]].<ref name=":3" /><ref name=":5" /><ref name=":8"/><ref>{{Cite journal|last1=Sathya|first1=G. R.|last2=Krishnamurthy|first2=N.|last3=Veliath|first3=Susheela|last4=Arulneyam|first4=Jayanthi|last5=Venkatachalam|first5=J.|date=2017|title=F wave index: A diagnostic tool for peripheral neuropathy|journal=The Indian Journal of Medical Research|volume=145|issue=3|pages=353–357|doi=10.4103/ijmr.IJMR_1087_14|issn=0971-5916|pmc=5555064|pmid=28749398|doi-access=free}}</ref> As the orthodromic impulse reaches innervated muscle fibers, a strong direct motor response (M) is evoked in these muscle fibers, resulting in a primary [[Compound muscle action potential|compound muscle action potential (CMAP)]].<ref name=":2" /><ref name=":5" /> As the antidromic impulse reaches the [[Soma (biology)|cell bodies]] within the [[Anterior horn of spinal cord|anterior horn]] of the motor neuron pool by retrograde transmission, a select portion of these alpha motor neurons, (roughly 5-10% of available motor neurons), 'backfire' or rebound.<ref name=":1" /><ref name=":2" /><ref name=":3" /><ref name=":4" /> This antidromic 'backfiring' elicits an orthodromic impulse that follows back down the alpha motor neuron, towards innervated muscle fibers. Conventionally, axonal segments of motor neurons previously depolarized by preceding antidromic impulses enter a [[Hyperpolarization (biology)|hyperpolarized]] state, disallowing the travel of impulses along them.<ref name=":7">{{Cite book|last=Kimura|first=Jun|title=Clinical Neurophysiology of Motor Neuron Diseases|chapter=Peripheral nerve conduction studies and neuromuscular junction testing|date=2004-01-01|chapter-url=http://www.sciencedirect.com/science/article/pii/S1567423104040122|series=Handbook of Clinical Neurophysiology |volume=4|pages=241–270|editor-last=Eisen|editor-first=Andrew|publisher=Elsevier|language=en|access-date=2020-02-26|doi=10.1016/S1567-4231(04)04012-2|isbn=978-0-444-51359-5}}</ref> However, these same axonal segments remains excitable or relatively depolarized for a sufficient period of time, allowing for rapid antidromic backfiring, and thus the continuation of the orthodromic impulse towards innervated muscle fibers.<ref name=":7" /><ref name=":8">{{Cite journal|last1=Panayiotopoulos|first1=C. P.|last2=Chroni|first2=E.|date=1996|title=F-waves in clinical neurophysiology: a review, methodological issues and overall value in peripheral neuropathies|journal=Electroencephalography and Clinical Neurophysiology|volume=101|issue=5|pages=365–374|issn=0013-4694|pmid=8913188}}</ref> This successive orthodromic stimulus then evokes a smaller population of muscle fibers, resulting in a smaller CMAP known as an F-wave.<ref name=":2" />


Several physiological factors may possibly influence the presence of F-waves after peripheral nerve stimulation. The shape and size of F-waves, along with the probability of their presence is small, as a high degree of variability exists in motor unit (MU) activation for any given stimulation.<ref name=":3" /> Thus, the generation of CMAP's which elicit F-waves is subject to the variability in activation of motor units in a given pool over successive stimuli.<ref name=":6" /> Moreover, stimulation of peripheral nerve fibers account for both orthodromic impulses (along sensory fibers, towards the dorsal horn), as well as antidromic activity (along alpha motor neurons towards the [[Anterior horn of spinal cord|ventral horn]]).<ref name=":3" /> Antidromic activity along collateral branches of alpha motor neurons may result in the activation of inhibitory [[Renshaw cell]]s or direct inhibitory collaterals between motorneurons.<ref>{{Cite journal|last1=Moore|first1=Niall J.|last2=Bhumbra|first2=Gardave S.|last3=Foster|first3=Joshua D.|last4=Beato|first4=Marco|date=2015-10-07|title=Synaptic Connectivity between Renshaw Cells and Motoneurons in the Recurrent Inhibitory Circuit of the Spinal Cord|journal=The Journal of Neuroscience|volume=35|issue=40|pages=13673–13686|doi=10.1523/JNEUROSCI.2541-15.2015|issn=0270-6474|pmc=4595620|pmid=26446220}}</ref> Inhibition by these means may lower excitability of adjacent motor neurons and decrease the potential for antidromic backfiring and resultant F-waves; although it has been argued Renshaw cells preferentially inhibit smaller alpha motor neurons limited influence on modulation of antidromic backfiring.<ref name=":5" />
Several physiological factors may possibly influence the presence of F-waves after peripheral nerve stimulation. The shape and size of F-waves, along with the probability of their presence is small, as a high degree of variability exists in motor unit (MU) activation for any given stimulation.<ref name=":3" /> Thus, the generation of CMAP's which elicit F-waves is subject to the variability in activation of motor units in a given pool over successive stimuli.<ref name=":6" /> Moreover, stimulation of peripheral nerve fibers account for both orthodromic impulses (along sensory fibers, towards the dorsal horn), as well as antidromic activity (along alpha motor neurons towards the [[Anterior horn of spinal cord|ventral horn]]).<ref name=":3" /> Antidromic activity along collateral branches of alpha motor neurons may result in the activation of inhibitory [[Renshaw cell]]s or direct inhibitory collaterals between motorneurons.<ref>{{Cite journal|last1=Moore|first1=Niall J.|last2=Bhumbra|first2=Gardave S.|last3=Foster|first3=Joshua D.|last4=Beato|first4=Marco|date=2015-10-07|title=Synaptic Connectivity between Renshaw Cells and Motoneurons in the Recurrent Inhibitory Circuit of the Spinal Cord|journal=The Journal of Neuroscience|volume=35|issue=40|pages=13673–13686|doi=10.1523/JNEUROSCI.2541-15.2015|issn=0270-6474|pmc=4595620|pmid=26446220}}</ref> Inhibition by these means may lower excitability of adjacent motor neurons and decrease the potential for antidromic backfiring and resultant F-waves; although it has been argued Renshaw cells preferentially inhibit smaller alpha motor neurons limited influence on modulation of antidromic backfiring.<ref name=":5" />


Because a different population of anterior horn cells is stimulated with each stimulation, F waves are characterized as ubiquitous, low amplitude, late motor responses, which can vary in amplitude, latency and configuration across a series of stimuli.<ref name=":3" /><ref>{{Cite journal|last1=Fisher|first1=Morris A.|last2=Patil|first2=Vijaya K.|last3=Webber|first3=Charles L.|date=2015|title=Recurrence Quantification Analysis of F-Waves and the Evaluation of Neuropathies|journal=Neurology Research International|volume=2015|pages=183608|doi=10.1155/2015/183608|issn=2090-1852|pmc=4672360|pmid=26688754|doi-access=free}}</ref>
Because a different population of anterior horn cells is stimulated with each stimulation, F waves are characterized as ubiquitous, low amplitude, late motor responses, which can vary in amplitude, latency and configuration across a series of stimuli.<ref name=":3" /><ref>{{Cite journal|last1=Fisher|first1=Morris A.|last2=Patil|first2=Vijaya K.|last3=Webber|first3=Charles L.|date=2015|title=Recurrence Quantification Analysis of F-Waves and the Evaluation of Neuropathies|journal=Neurology Research International|volume=2015|article-number=183608|doi=10.1155/2015/183608|issn=2090-1852|pmc=4672360|pmid=26688754|doi-access=free}}</ref>


== Properties ==
== Properties ==

Latest revision as of 07:18, 30 September 2025

Template:Short description Script error: No such module "about". In neuroscience, an F wave is one of several motor responses which may follow the direct motor response (M) evoked by electrical stimulation of peripheral motor or mixed (sensory and motor) nerves.[1] F-waves are the second of two late voltage changes observed after stimulation is applied to the skin surface above the distal region of a nerve, in addition to the H-reflex (Hoffman's Reflex) which is a muscle reaction in response to electrical stimulation of innervating sensory fibers.[2][3] Traversal of F-waves along the entire length of peripheral nerves between the spinal cord and muscle, allows for assessment of motor nerve conduction between distal stimulation sites in the arm and leg, and related motoneurons (MN's) in the cervical and lumbosacral cord.[4] F-waves are able to assess both afferent and efferent loops of the alpha motor neuron in its entirety.[5] As such, various properties of F-wave motor nerve conduction are analyzed in nerve conduction studies (NCS),[6] and often used to assess polyneuropathies, resulting from states of neuronal demyelination and loss of peripheral axonal integrity.[1][7][8]

With respect to its nomenclature, the F-wave is so named as it was initially studied in the smaller muscles of the foot.[9] The observation of F-waves in the same motor units (MU) as those present in the direct motor response (M),[10] along with the presence of F-waves in deafferented animal and human models,[11] indicates that F-waves require direct activation of motor axons to be elicited,[12] and do not involve conduction along afferent sensory nerves. Thus, the F-wave is considered a wave, as opposed to a reflex.

Physiology

F-waves are evoked by strong electrical stimuli (supramaximal) applied to the skin surface above the distal portion of a nerve.[3] This impulse travels both in orthodromic fashion (towards the muscle fibers) and antidromic fashion (towards the cell body in the spinal cord) along the alpha motor neuron.[4][7][13][14] As the orthodromic impulse reaches innervated muscle fibers, a strong direct motor response (M) is evoked in these muscle fibers, resulting in a primary compound muscle action potential (CMAP).[3][7] As the antidromic impulse reaches the cell bodies within the anterior horn of the motor neuron pool by retrograde transmission, a select portion of these alpha motor neurons, (roughly 5-10% of available motor neurons), 'backfire' or rebound.[2][3][4][5] This antidromic 'backfiring' elicits an orthodromic impulse that follows back down the alpha motor neuron, towards innervated muscle fibers. Conventionally, axonal segments of motor neurons previously depolarized by preceding antidromic impulses enter a hyperpolarized state, disallowing the travel of impulses along them.[15] However, these same axonal segments remains excitable or relatively depolarized for a sufficient period of time, allowing for rapid antidromic backfiring, and thus the continuation of the orthodromic impulse towards innervated muscle fibers.[15][13] This successive orthodromic stimulus then evokes a smaller population of muscle fibers, resulting in a smaller CMAP known as an F-wave.[3]

Several physiological factors may possibly influence the presence of F-waves after peripheral nerve stimulation. The shape and size of F-waves, along with the probability of their presence is small, as a high degree of variability exists in motor unit (MU) activation for any given stimulation.[4] Thus, the generation of CMAP's which elicit F-waves is subject to the variability in activation of motor units in a given pool over successive stimuli.[11] Moreover, stimulation of peripheral nerve fibers account for both orthodromic impulses (along sensory fibers, towards the dorsal horn), as well as antidromic activity (along alpha motor neurons towards the ventral horn).[4] Antidromic activity along collateral branches of alpha motor neurons may result in the activation of inhibitory Renshaw cells or direct inhibitory collaterals between motorneurons.[16] Inhibition by these means may lower excitability of adjacent motor neurons and decrease the potential for antidromic backfiring and resultant F-waves; although it has been argued Renshaw cells preferentially inhibit smaller alpha motor neurons limited influence on modulation of antidromic backfiring.[7]

Because a different population of anterior horn cells is stimulated with each stimulation, F waves are characterized as ubiquitous, low amplitude, late motor responses, which can vary in amplitude, latency and configuration across a series of stimuli.[4][17]

Properties

F waves can be analyzed by several properties including:

  • amplitude (μV) - height or voltage of F wave
  • duration (ms) - length of F wave
  • latency (ms) - period between initial stimulation and F wave elicitation

Measurements

Several measurements can be done on the F responses, including:[7][13]

  • minimal and maximal F wave latencies (ms) - frequently used in the assessment of demyelinating neuropathic conditions including Guillain-Barré syndrome.
  • chronodispersion - difference in maximal and minimal latencies across a series of F waves
  • F wave persistence - measure of alpha motor neuron excitability calculated as the number of F responses elicited divided by the number of stimuli presented.

The minimal F wave latency is typically 25-32 ms in the upper extremities and 45-56 ms in the lower extremities.

F wave persistence is the number of F waves obtained per the number of stimulations, which is normally 80-100% (or above 50%).

See also

References

Template:Reflist

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  6. ↑ Script error: No such module "Citation/CS1".
  7. ↑ a b c d e Script error: No such module "Citation/CS1".
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  10. ↑ Script error: No such module "Citation/CS1".
  11. ↑ a b Script error: No such module "Citation/CS1".
  12. ↑ Script error: No such module "citation/CS1".
  13. ↑ a b c Script error: No such module "Citation/CS1".
  14. ↑ Script error: No such module "Citation/CS1".
  15. ↑ a b Script error: No such module "citation/CS1".
  16. ↑ Script error: No such module "Citation/CS1".
  17. ↑ Script error: No such module "Citation/CS1".
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