F wave

Last updated

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]

Contents

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:

Measurements

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

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

Related Research Articles

<span class="mw-page-title-main">Nerve</span> Enclosed, cable-like bundle of axons in the peripheral nervous system

A nerve is an enclosed, cable-like bundle of nerve fibers in the peripheral nervous system.

<span class="mw-page-title-main">Motor neuron</span> Nerve cell sending impulse to muscle

A motor neuron is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly control effector organs, mainly muscles and glands. There are two types of motor neuron – upper motor neurons and lower motor neurons. Axons from upper motor neurons synapse onto interneurons in the spinal cord and occasionally directly onto lower motor neurons. The axons from the lower motor neurons are efferent nerve fibers that carry signals from the spinal cord to the effectors. Types of lower motor neurons are alpha motor neurons, beta motor neurons, and gamma motor neurons.

<span class="mw-page-title-main">Somatic nervous system</span> Part of the peripheral nervous system

The somatic nervous system (SNS), also known as voluntary nervous system, is a part of the peripheral nervous system (PNS) that links brain and spinal cord to skeletal muscles under conscious control, as well as to sensory receptors in the skin. The other part complementary to the somatic nervous system is the autonomic nervous system (ANS).

Fibrillation is the rapid, irregular, and unsynchronized contraction of muscle fibers. An important occurrence is with regard to the heart.

<span class="mw-page-title-main">Muscle spindle</span> Innervated muscle structure involved in reflex actions and proprioception

Muscle spindles are stretch receptors within the body of a skeletal muscle that primarily detect changes in the length of the muscle. They convey length information to the central nervous system via afferent nerve fibers. This information can be processed by the brain as proprioception. The responses of muscle spindles to changes in length also play an important role in regulating the contraction of muscles, for example, by activating motor neurons via the stretch reflex to resist muscle stretch.

<span class="mw-page-title-main">Electromyography</span> Electrodiagnostic medicine technique

Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyograph detects the electric potential generated by muscle cells when these cells are electrically or neurologically activated. The signals can be analyzed to detect abnormalities, activation level, or recruitment order, or to analyze the biomechanics of human or animal movement. Needle EMG is an electrodiagnostic medicine technique commonly used by neurologists. Surface EMG is a non-medical procedure used to assess muscle activation by several professionals, including physiotherapists, kinesiologists and biomedical engineers. In computer science, EMG is also used as middleware in gesture recognition towards allowing the input of physical action to a computer as a form of human-computer interaction.

Renshaw cells are inhibitory interneurons found in the gray matter of the spinal cord, and are associated in two ways with an alpha motor neuron.

Axonotmesis is an injury to the peripheral nerve of one of the extremities of the body. The axons and their myelin sheath are damaged in this kind of injury, but the endoneurium, perineurium and epineurium remain intact. Motor and sensory functions distal to the point of injury are completely lost over time leading to Wallerian degeneration due to ischemia, or loss of blood supply. Axonotmesis is usually the result of a more severe crush or contusion than neurapraxia.

<span class="mw-page-title-main">Nerve conduction study</span> Diagnostic test for nerve function

A nerve conduction study (NCS) is a medical diagnostic test commonly used to evaluate the function, especially the ability of electrical conduction, of the motor and sensory nerves of the human body. These tests may be performed by medical specialists such as clinical neurophysiologists, physical therapists, physiatrists, and neurologists who subspecialize in electrodiagnostic medicine. In the United States, neurologists and physiatrists receive training in electrodiagnostic medicine as part of residency training and in some cases acquire additional expertise during a fellowship in clinical neurophysiology, electrodiagnostic medicine, or neuromuscular medicine. Outside the US, clinical neurophysiologists learn needle EMG and NCS testing.

The jaw jerk reflex or the masseter reflex is a stretch reflex used to test the status of a patient's trigeminal nerve and to help distinguish an upper cervical cord compression from lesions that are above the foramen magnum. The mandible—or lower jaw—is tapped at a downward angle just below the lips at the chin while the mouth is held slightly open. In response, the masseter muscles will jerk the mandible upwards. Normally this reflex is absent or very slight. However, in individuals with upper motor neuron lesions the jaw jerk reflex can be quite pronounced.

<span class="mw-page-title-main">Gamma motor neuron</span> Lower motor neuron involved in muscle contraction

A gamma motor neuron, also called gamma motoneuron, or fusimotor neuron, is a type of lower motor neuron that takes part in the process of muscle contraction, and represents about 30% of (Aγ) fibers going to the muscle. Like alpha motor neurons, their cell bodies are located in the anterior grey column of the spinal cord. They receive input from the reticular formation of the pons in the brainstem. Their axons are smaller than those of the alpha motor neurons, with a diameter of only 5 μm. Unlike the alpha motor neurons, gamma motor neurons do not directly adjust the lengthening or shortening of muscles. However, their role is important in keeping muscle spindles taut, thereby allowing the continued firing of alpha neurons, leading to muscle contraction. These neurons also play a role in adjusting the sensitivity of muscle spindles.

<span class="mw-page-title-main">Nerve conduction velocity</span> Speed at which an electrochemical impulse propagates down a neural pathway

In neuroscience, nerve conduction velocity (CV) is the speed at which an electrochemical impulse propagates down a neural pathway. Conduction velocities are affected by a wide array of factors, which include age, sex, and various medical conditions. Studies allow for better diagnoses of various neuropathies, especially demyelinating diseases as these conditions result in reduced or non-existent conduction velocities. CV is an important aspect of nerve conduction studies.

<span class="mw-page-title-main">Microneurography</span>

Microneurography is a neurophysiological method employed to visualize and record the traffic of nerve impulses that are conducted in peripheral nerves of waking human subjects. It can also be used in animal recordings. The method has been successfully employed to reveal functional properties of a number of neural systems, e.g. sensory systems related to touch, pain, and muscle sense as well as sympathetic activity controlling the constriction state of blood vessels. To study nerve impulses of an identified nerve, a fine tungsten needle microelectrode is inserted into the nerve and connected to a high input impedance differential amplifier. The exact position of the electrode tip within the nerve is then adjusted in minute steps until the electrode discriminates nerve impulses of interest. A unique feature and a significant strength of the microneurography method is that subjects are fully awake and able to cooperate in tests requiring mental attention, while impulses in a representative nerve fibre or set of nerve fibres are recorded, e.g. when cutaneous sense organs are stimulated or subjects perform voluntary precision movements.

<span class="mw-page-title-main">Group C nerve fiber</span> One of three classes of nerve fiber in the nervous system

Group C nerve fibers are one of three classes of nerve fiber in the central nervous system (CNS) and peripheral nervous system (PNS). The C group fibers are unmyelinated and have a small diameter and low conduction velocity, whereas Groups A and B are myelinated. Group C fibers include postganglionic fibers in the autonomic nervous system (ANS), and nerve fibers at the dorsal roots. These fibers carry sensory information.

Motor unit number estimation (MUNE) is a technique that uses electromyography to estimate the number of motor units in a muscle.

<span class="mw-page-title-main">Axon reflex</span>

The axon reflex is the response stimulated by peripheral nerves of the body that travels away from the nerve cell body and branches to stimulate target organs. Reflexes are single reactions that respond to a stimulus making up the building blocks of the overall signaling in the body's nervous system. Neurons are the excitable cells that process and transmit these reflex signals through their axons, dendrites, and cell bodies. Axons directly facilitate intercellular communication projecting from the neuronal cell body to other neurons, local muscle tissue, glands and arterioles. In the axon reflex, signaling starts in the middle of the axon at the stimulation site and transmits signals directly to the effector organ skipping both an integration center and a chemical synapse present in the spinal cord reflex. The impulse is limited to a single bifurcated axon, or a neuron whose axon branches into two divisions and does not cause a general response to surrounding tissue.

The Golgi tendon reflex (also called inverse stretch reflex, autogenic inhibition, tendon reflex) is an inhibitory effect on the muscle resulting from the muscle tension stimulating Golgi tendon organs (GTO) of the muscle, and hence it is self-induced. The reflex arc is a negative feedback mechanism preventing too much tension on the muscle and tendon. When the tension is extreme, the inhibition can be so great it overcomes the excitatory effects on the muscle's alpha motoneurons causing the muscle to suddenly relax. This reflex is also called the inverse myotatic reflex, because it is the inverse of the stretch reflex.

Group A nerve fibers are one of the three classes of nerve fiber as generally classified by Erlanger and Gasser. The other two classes are the group B nerve fibers, and the group C nerve fibers. Group A are heavily myelinated, group B are moderately myelinated, and group C are unmyelinated.

<span class="mw-page-title-main">Neuromechanics</span> Interdisciplinary field

Neuromechanics is an interdisciplinary field that combines biomechanics and neuroscience to understand how the nervous system interacts with the skeletal and muscular systems to enable animals to move. In a motor task, like reaching for an object, neural commands are sent to motor neurons to activate a set of muscles, called muscle synergies. Given which muscles are activated and how they are connected to the skeleton, there will be a corresponding and specific movement of the body. In addition to participating in reflexes, neuromechanical process may also be shaped through motor adaptation and learning.

<span class="mw-page-title-main">Cutaneous reflex in human locomotion</span>

Cutaneous, superficial, or skin reflexes, are activated by skin receptors and play a valuable role in locomotion, providing quick responses to unexpected environmental challenges. They have been shown to be important in responses to obstacles or stumbling, in preparing for visually challenging terrain, and for assistance in making adjustments when instability is introduced. In addition to the role in normal locomotion, cutaneous reflexes are being studied for their potential in enhancing rehabilitation therapy (physiotherapy) for people with gait abnormalities.

References

  1. 1 2 Neuromuscular function and disease : basic, clinical, and electrodiagnostic aspects. Brown, William F. (William Frederick), 1939-, Bolton, Charles Francis, 1932-, Aminoff, Michael J. (Michael Jeffrey) (1st ed.). Philadelphia: Saunders. 2002. ISBN   0-7216-8922-1. OCLC   46873002.{{cite book}}: CS1 maint: others (link)
  2. 1 2 Smith, M; Kofke, WA; Citerio, G (2016). Oxford Textbook of Neurocritical Care. Oxford University Press. p. 175.
  3. 1 2 3 4 5 Jerath, Nivedita; Kimura, Jun (2019). "F wave, A wave, H reflex, and blink reflex". Clinical Neurophysiology: Basis and Technical Aspects. Handbook of Clinical Neurology. Vol. 160. pp. 225–239. doi:10.1016/B978-0-444-64032-1.00015-1. ISBN   9780444640321. ISSN   0072-9752. PMID   31277850. S2CID   195813560.
  4. 1 2 3 4 5 6 Fisher, Morris A. (2007-02-02). "F-waves--physiology and clinical uses". TheScientificWorldJournal. 7: 144–160. doi: 10.1100/tsw.2007.49 . ISSN   1537-744X. PMC   5901048 . PMID   17334607.
  5. 1 2 Katirji, Bashar. (2007). Electromyography in clinical practice : a case study approach (2nd ed.). Philadelphia: Mosby Elsevier. ISBN   978-0-323-07034-8. OCLC   324995633.
  6. ↑ Mallik, A.; Weir, A. I. (2005). "Nerve conduction studies: essentials and pitfalls in practice". Journal of Neurology, Neurosurgery, and Psychiatry. 76 (Suppl 2): ii23–31. doi:10.1136/jnnp.2005.069138. ISSN   0022-3050. PMC   1765692 . PMID   15961865.
  7. 1 2 3 4 5 Fisher, Morris A. (1992). "AAEM minimonograph #13: H reflexes and F waves: Physiology and clinical indications". Muscle & Nerve. 15 (11): 1223–1233. doi:10.1002/mus.880151102. ISSN   1097-4598. PMID   1488060. S2CID   6174526.
  8. ↑ Lachman, T; Shahani, B T; Young, R R (1980). "Late responses as aids to diagnosis in peripheral neuropathy". Journal of Neurology, Neurosurgery, and Psychiatry. 43 (2): 156–162. doi:10.1136/jnnp.43.2.156. ISSN   0022-3050. PMC   490491 . PMID   6244369.
  9. ↑ Magladery, J. W.; McDOUGAL, D. B. (1950). "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". Bulletin of the Johns Hopkins Hospital. 86 (5): 265–290. ISSN   0097-1383. PMID   15414383.
  10. ↑ Wulff, C. H.; Gilliatt, R. W. (1979). "F waves in patients with hand wasting caused by a cervical rib and band". Muscle & Nerve. 2 (6): 452–457. doi:10.1002/mus.880020606. ISSN   0148-639X. PMID   514311. S2CID   2423723.
  11. 1 2 Fox, J E; Hitchcock, E R (1987). "F wave size as a monitor of motor neuron excitability: the effect of deafferentation". Journal of Neurology, Neurosurgery, and Psychiatry. 50 (4): 453–459. doi:10.1136/jnnp.50.4.453. ISSN   0022-3050. PMC   1031882 . PMID   3585357.
  12. ↑ Trontelj, JV (1973). A study of the F response by single fiber electromyography, in Desmedt JE (ed): New Developments in Electromyography and Clinical Neurophysiology. Basel: Karger. pp. 318–322.
  13. 1 2 3 Panayiotopoulos, C. P.; Chroni, E. (1996). "F-waves in clinical neurophysiology: a review, methodological issues and overall value in peripheral neuropathies". Electroencephalography and Clinical Neurophysiology. 101 (5): 365–374. ISSN   0013-4694. PMID   8913188.
  14. ↑ Sathya, G. R.; Krishnamurthy, N.; Veliath, Susheela; Arulneyam, Jayanthi; Venkatachalam, J. (2017). "F wave index: A diagnostic tool for peripheral neuropathy". The Indian Journal of Medical Research. 145 (3): 353–357. doi: 10.4103/ijmr.IJMR_1087_14 (inactive 2024-09-11). ISSN   0971-5916. PMC   5555064 . PMID   28749398.{{cite journal}}: CS1 maint: DOI inactive as of September 2024 (link)
  15. 1 2 Kimura, Jun (2004-01-01). "Peripheral nerve conduction studies and neuromuscular junction testing". In Eisen, Andrew (ed.). Clinical Neurophysiology of Motor Neuron Diseases. Handbook of Clinical Neurophysiology. Vol. 4. Elsevier. pp. 241–270. doi:10.1016/S1567-4231(04)04012-2. ISBN   9780444513595 . Retrieved 2020-02-26.
  16. ↑ Moore, Niall J.; Bhumbra, Gardave S.; Foster, Joshua D.; Beato, Marco (2015-10-07). "Synaptic Connectivity between Renshaw Cells and Motoneurons in the Recurrent Inhibitory Circuit of the Spinal Cord". The Journal of Neuroscience. 35 (40): 13673–13686. doi:10.1523/JNEUROSCI.2541-15.2015. ISSN   0270-6474. PMC   4595620 . PMID   26446220.
  17. ↑ Fisher, Morris A.; Patil, Vijaya K.; Webber, Charles L. (2015). "Recurrence Quantification Analysis of F-Waves and the Evaluation of Neuropathies". Neurology Research International. 2015: 183608. doi: 10.1155/2015/183608 . ISSN   2090-1852. PMC   4672360 . PMID   26688754.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.