Жүйке жүйесіндегі F толқыны және оның диагностикалық маңызы

the term as it applies to neuroscience
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. 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. 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. F waves are able to assess both afferent and efferent loops of the alpha motor neuron in its entirety. As such, various properties of F wave motor nerve conduction are analyzed in nerve conduction studies (NCS), and often used to assess polyneuropathies, resulting from states of neuronal demyelination and loss of peripheral axonal integrity. With respect to its nomenclature, the F wave is so named as it was initially studied in the smaller muscles of the foot. The observation of F waves in the same motor units (MU) as those present in the direct motor response (M), along with the presence of F waves in deafferented animal and human models, indicates that F waves require direct activation of motor axons to be elicited, and do not involve conduction along afferent sensory nerves. Thus, the F wave is considered a wave, as opposed to a reflex.

F waves are evoked by strong electrical stimuli (supramaximal) applied to the skin surface above the distal portion of a nerve. 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). 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. This successive orthodromic stimulus then evokes a smaller population of muscle fibers, resulting in a smaller CMAP known as an F wave. 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.