Axonal Conduction Velocity Measurement

Experimental brain research, 2003

Intra-axonal recordings were performed in ventral roots of rats in vitro to study the conduction velocity and firing threshold properties of motoneuron axons. Mean values +/- SD were 30.5+/-5.6 m/s for conduction velocity and 11.6+/-4.5 mV for the depolarization from the resting potential required to reach firing threshold (threshold depolarization). Conduction velocity varied inversely and significantly with threshold depolarization ( P=0.0002 by linear regression). This relationship was evident even after accounting for variation in conduction velocity associated with action potential amplitude, injected current amplitude, or body weight. Conduction velocity also varied inversely with the time to action potential onset during just-threshold current pulse injection. These data suggest that the time course of depolarization leading to action potential initiation contributes to the speed of conduction in motoneuron axons.

Clinical Neurophysiology, 2020

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IEEE Transactions on Biomedical Engineering, 1996

The sampled compound action potential (CAP) data sequence was expressed as the circular convolution of the delay sequence and the sampled single fiber action potential (SFAP) data sequence. An algorithm, based on Hirose's method [l], was then developed to separate the delay sequence from the sampled CAP data sequence, and the nerve conduction velocity distribution (NCVD) was consequently calculated from the delay sequence. The NCVD was found to be the product of the amplitude of the SFAP and the number of fibers. Simulations show that the estimated results were in good agreement with the calculated results. Experiments were performed on ten sciatic nerves from five bullfrogs (Rana pipens) using two independent variables: interelectrode distance and stimulus current strength. The results estimated from CAP's recorded under each condition reflect the corresponding feature of NCVD of the condition. The advantage of the technique is to provide detailed information about both slow and fast conducting fibers. This technique also offers the possibility to directly calculate the nerve fiber diameter distribution from the sampled CAP data sequences.

Current opinion in neurobiology, 2018

Axons link distant brain regions and are usually considered as simple transmission cables in which reliable propagation occurs once an action potential has been generated. Safe propagation of action potentials relies on specific ion channel expression at strategic points of the axon such as nodes of Ranvier or axonal branch points. However, while action potentials are generally considered as the quantum of neuronal information, their signaling is not entirely digital. In fact, both their shape and their conduction speed have been shown to be modulated by activity, leading to regulations of synaptic latency and synaptic strength. We report here newly identified mechanisms of (1) safe spike propagation along the axon, (2) compartmentalization of action potential shape in the axon, (3) analog modulation of spike-evoked synaptic transmission and (4) alteration in conduction time after persistent regulation of axon morphology in central neurons. We discuss the contribution of these regul...

Medical Engineering & Physics, 2004

Nerve conduction velocity distribution (CVD) is a very useful tool to examine the state and function of nerves. Only one record of compound action potential (CAP) may be sufficient to determine the CVD if the shape functions of the single fiber action potentials (SFAP) of fibers are known. Otherwise, CAP recordings from different locations are necessary to determine CVD. In this case, we confront the problem of whether the shape of the CVD changes along the nerve, because many methods that attempt to determine the CVD are based on the assumption that the CVD is invariant along the nerve. There is not a complete solution to this problem, but there are many suggestions allied with the recording conditions to minimise this effect. The other effect that may influence both shapes of CAP and CVD along the nerve is the volume conductor effect. If a suitable model could isolate and eliminate the volume conductor effect, then the spatial variation of CVD may be attributed to the natural conditions of the nerve. In this study, we followed a procedure to eliminate volume conductor effect and then applied our previously published model to examine the spatial variations in CVD. The results show that CVDs estimated at discrete points along the nerve trunk have significantly different patterns. Consequently, it may be concluded that CVD is not uniform along an isolated nerve trunk contrary to the assumptions of the most CVD estimation methods.

Brain Research, 1996

Impulse activity in axons generates aftereffects on membrane excitability that can alter the conduction velocity of subsequently conducted impulses. We used a computerized stimulus pattern (a 1 Hz stimulus period followed by a period of repeated short bursts at 200 Hz) to assess in vivo activity-dependent changes in conduction latency of functionally identified rat cutaneous afferents conducting in the A 13 range. Several different parameters of activity dependence were measured: burst supernormality, the average increase in conduction latency following conditioning with a single preceding impulse during high frequency burst stimulation; burst subnormality, the average latency increase during each burst; depression, a long-term increase in latency caused by the high frequency stimulation. The data show that different mechanosensitive A/3 afferents with overlapping resting conduction velocities exhibit activity-dependent changes in conduction latency that are characteristic of their particular functions.

Neuron, 2019

The study by Ng et al. (2019) revealed a mechanism by which the signal elicited by pheromone is amplified in the ORNs that promote courtship behavior (see Figure 1). The mechanism involves PPK25, a member of DEG/ENaC channels that plays a key role in signal amplification and transduction. The CBM in PPK25 channel directly interacts with calmodulin during the rise of the intracellular calcium level, which is spurred by the activation of a ligand-gated OR, eventually generating signal amplification. Interestingly, the CBM is also found in other species, including mouse and human, and the DEG/ENaC channels are expressed in different types of sensory neurons that mediate mechanosensation, baro-reception, proprioception, nociception, and taste reception. This work will provide a foundation for understanding signal amplification in other neuron types.

Proceedings of the National Academy of Sciences of the United States of America, 1975

This note calls attention to the facts that (1) the conduction velocities of central axons may not be pre- dicted on the basis of diameter alone, and (il) that such struc-

The Journal of Membrane Biology, 1969

A new mode of voltage clamping in the squid giant axon is introduced and its advantages are analyzed, tested, and utilized to investigate membrane conductances and capacity. This method replaces the constant command potentials of the standard voltage clamp with potentials which vary with time. Some of the advantages in using the varying potential clamp are: (1) slowly varying potentials generate practically pure IK; (2) rapidly varying potentials generate practically pure INa; (3) triangular waves generate, under proper conditions, pure capacity currents and easy-to-analyze leakage currents; (4) the method gives direct, on-line display of sodium or potassium I-V characteristics within milliseconds; (5) it enables rapid and accurate ENa and E K determinations; and (6) it enables simple and accurate determination of C m. The method was utilized to study the effects of various ions on membrane conductances and the effects of ionic composition, ionic strength, and temperature on membrane capacity. Membrane capacity was found to be practically independent of frequency in the 200 to 2,000 Hz range. Replacement of external sodium by Ca ++, by impermeable Tris +, or even by dextrose or sucrose (low ionic-strength solutions) had negligible effects on C m. C m showed a small, positive temperature coefficient of 1.39 % per ~ in the 3 to 21 ~ range, and little change with temperature in the 20 to 40 ~ range. Above 40 ~ both C m and gL increased considerably with temperature.

Experimental Neurology, 1974

spikes were recorded from the cell bodies of antidromically activated callosal axons in rabbit visual cortex. Callosal axons were stimulated near their terminals in the contralateral cortex. The primary method for differentiating antidromic from synaptic activation was the test for collision of impulses. Additional tests provided further confirmation of antidromic activation. A decrease in antidromic latency always occurred when an antidromic volley followed either a spontaneous spike or a preceding antidromically elicited spike at appropriate intervals. The time course and magnitude of the latency decrease coincided with that of a threshold decrease at the site of electrical stimulation. The antidromic latency decrease was primarily due to an increase in axon conduction velocity. These systematic variations in conduction velocity and stimulus threshold strongly suggest that an afterdepolarization follows the activation of callosal axons. While such afterpotentials are known to occur in unmyelinated C fibers, the present evidence suggests that they also occur in the smallest of myelinated axons.