F wave
Encyclopedia
In neuroscience
, an F wave is the second of two voltage
changes observed after electrical stimulation is applied to the skin surface above the distal region of a nerve
. F waves are often used to measure nerve conduction velocity
, and are particularly useful for evaluating conduction problems in the proximal region of nerves (i.e., portions of nerves near the spinal cord
).
It's called F wave because it was initially recorded in the foot muscles.
s of the spinal cord). (These directions are also known as orthodromic
and antidromic
, respectively.) When the orthodromic stimulus reaches the muscle fiber, it elicits a strong M-response indicative of muscle contraction
. When the antidromic stimulus reaches the motor neuron cell bodies, a small portion of the motor neurons backfire and orthodromic wave travels back down the nerve towards the muscle. This reflected stimulus evokes small proportion of the muscle fibers causing a small,second CMAP called the F wave.
Because a different population of anterior horn cells is stimulated with each stimulation, each F wave have a slightly different shape, amplitude and latency.
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%).
Neuroscience
Neuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...
, an F wave is the second of two voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
changes observed after electrical stimulation is applied to the skin surface above the distal region of a nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
. F waves are often used to measure nerve conduction velocity
Nerve conduction velocity
Nerve conduction velocity is the speed at which an electrochemical signal propagates down a neural pathway. Many things can affect this, including axon diameter, myelination, the internal resistance of the axon, and temperature. Nerve conduction velocity differs from species to species, and to a...
, and are particularly useful for evaluating conduction problems in the proximal region of nerves (i.e., portions of nerves near the spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
).
It's called F wave because it was initially recorded in the foot muscles.
Overview
In a typical F wave study, a strong electrical stimulus (supramaximal stimulation) is applied to the skin surface above the distal portion of a nerve so that the impulse travels both distally (towards the muscle fiber) and proximally (back to the motor neuronMotor neuron
In vertebrates, the term motor neuron classically applies to neurons located in the central nervous system that project their axons outside the CNS and directly or indirectly control muscles...
s of the spinal cord). (These directions are also known as orthodromic
Orthodromic
An orthodromic impulse runs along an axon in its normal direction, away from the soma.In the heart, orthodromic may also refer to an impulse going in the correct direction from the atria to the ventricles, in contrast to some impulses in re-entry....
and antidromic
Antidromic
An antidromic impulse in an axon refers to conduction opposite of the normal direction. That is, it refers to conduction along the axon away from the axon terminal and towards the soma...
, respectively.) When the orthodromic stimulus reaches the muscle fiber, it elicits a strong M-response indicative of muscle contraction
Muscle contraction
Muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same...
. When the antidromic stimulus reaches the motor neuron cell bodies, a small portion of the motor neurons backfire and orthodromic wave travels back down the nerve towards the muscle. This reflected stimulus evokes small proportion of the muscle fibers causing a small,second CMAP called the F wave.
Because a different population of anterior horn cells is stimulated with each stimulation, each F wave have a slightly different shape, amplitude and latency.
Properties
F wave properties include:- amplitude (µVVoltThe volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
) - F wave height - duration (msMillisecondA millisecond is a thousandth of a second.10 milliseconds are called a centisecond....
) - length of F wave - latency (ms) - period between F wave and initial stimulation
F wave measurements
Several measurements can be done on the F responses, including minimal and maximal latencies, and F wave persistence.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%).