Nerve Conduction in Cats: 50-120 m/s and Three Conditions

A cat's fastest nerve fibers carry signals at 50 to 120 meters per second, and its slowest at roughly 0.5 to 2 m/s, a spread of more than 100-fold inside one nerve. That is why a conduction study reports each fiber class separately rather than one headline number, and why a velocity is only readable when limb temperature, stimulus strength, and measured distance are printed beside it. A figure quoted without those three conditions cannot be compared with any reference range, not even the same laboratory's own.

Two families of fiber, two orders of speed

Myelinated A fibers run 3 to 20 micrometers across and conduct by jumping between nodes of Ranvier spaced roughly 0.5 to 1.5 mm apart along the axon. Unmyelinated C fibers are 0.3 to 1.5 micrometers wide, carry no myelin, and propagate continuously along the membrane, which costs them about 50 to 100 times the speed. In the cat sciatic nerve the largest motor axons sit at the top of the A range, commonly recorded at 50 to 90 m/s in a mature animal, while the C population in the same nerve bundle rarely climbs above 2 m/s. A single electrode pair records both, which is why the averaged waveform looks like a fast spike riding on a slow hump. Splitting a nerve this way is the same move as splitting a retina by photoreceptor class in feline color vision work.

Why 50 to 120 m/s is the working window

In myelinated fibers velocity scales roughly with diameter: a 12 micrometer axon lands near 60 m/s, a 20 micrometer axon near 120 m/s, a ratio close to 6 m/s per micrometer. The recording is simple arithmetic. Stimulate the nerve at two points, measure the difference in onset latency, divide by the distance between the two cathodes, and multiply by 10 to convert cm/ms into m/s. Ten centimeters of nerve and a 2.0 ms latency difference gives exactly 50 m/s. Because latency is read to 0.1 ms, a 0.1 ms misread across that 10 cm shifts the answer by 5 m/s, a 10 percent error created by a cursor placement. That single source of slop is why the distance must be at least 10 cm, and why shorter segments are rejected rather than corrected.

Condition one: limb temperature

A cat's core sits at 38.1 to 39.2 C (100.6 to 102.6 F), and the nerve should be recorded at 37 to 38.5 C. Every degree below 37 C costs roughly 1.5 to 2.5 m/s, so a limb that has been shaved and exposed for 20 minutes on a 22 C table can lose 6 to 10 m/s and mimic a demyelinating lesion. Warm the limb with a 40 C water blanket for 10 to 15 minutes, then re-check the skin over the nerve every 5 minutes with a probe rather than a thermometer across the room. Record the temperature next to the velocity, always.

Condition two: supramaximal stimulus and averaging

Use a 0.1 to 0.2 ms pulse and raise the current until the response amplitude stops growing, then set the dial 20 to 50 percent above that point, which is the supramaximal level. A submaximal stimulus recruits the slow fibers first and quietly drops 5 to 15 m/s off the top of the distribution. Average 8 to 32 responses with artifact rejection on, filter 2 Hz to 10 kHz, and place the ground between the recording and stimulating electrodes. Recording electrodes go 1 to 2 cm apart over the muscle belly, not over the tendon, or the amplitude falls by half and looks like axonal loss.

Condition three: distance, joint angle, anesthesia

Measure with calipers to the nearest millimeter along the straight line between cathodes, keep the joint at the same angle on both runs (a stifle held at 90 versus 120 degrees changes the path length by 1 to 2 cm), and hold anesthesia at a stable 1.0 to 1.5 times MAC for 15 minutes before the first trace. Ketamine boluses mid-run and neuromuscular blockers both destroy comparability, and a shivering cat produces a 50 Hz artifact that swamps the waveform. Record both limbs in the same order, in a room held at 22 to 24 C, and repeat the run after 10 minutes if the first two differ by more than 10 percent.

What a usable report lists

Like a white cell count, a velocity means something only with its conditions attached.

Item	Typical setting	Effect if omitted
Nerve temperature	37 to 38.5 C	1.5 to 2.5 m/s lost per degree
Stimulus strength	120 to 150 percent of maximal	5 to 15 m/s underestimate
Inter-cathode distance	10 cm or more	5 m/s error from a 0.1 ms misread
Responses averaged	8 to 32	50 Hz noise read as a late peak
Filter band	2 Hz to 10 kHz	2 to 10 kHz band: clipped or blurred
Contralateral limb	Same session, 2 limbs	Above 10 percent: repeat it

Individual variation is normal and large

Kittens are born with fibers that conduct at perhaps half the adult rate, reach 70 to 90 percent of adult values by 8 weeks, and finish myelinating between 6 and 12 months. A 3 kg cat and a 6 kg cat of the same age can differ by 5 to 10 m/s on the same nerve, which is why the opposite limb, not the textbook, is the control. After about 8 years a mild decline of 2 to 5 m/s is common and does not by itself mean disease. Pelvic limb nerves usually run 3 to 8 m/s faster than thoracic ones, and a side-to-side difference above 10 percent is worth repeating before it is called a lesion.

When the number stops being noise

A velocity under 40 m/s in a limb confirmed at 37 C or above, an amplitude below 50 percent of the opposite side, or a 20 percent drop across a 10 cm segment points to focal demyelination or entrapment rather than to a bad technique. Sudden rear limb weakness with cold paws, pain, and a loss of the femoral pulse is a saddle thrombus and needs a veterinarian within the hour, not a conduction study. Slow progressive knuckling, dragging, or a cat that stops jumping is a neurology workup with electromyography, and the conduction number is one line in that report, not the diagnosis.

Five steps before the next study

Warm the limb to 37 to 38.5 C and log the probe reading beside each velocity.
Set the stimulus 20 to 50 percent above maximal and average 16 responses minimum.
Keep the inter-cathode distance at 10 cm or longer and measure it with calipers.
Run the opposite limb in the same session and compare, not the reference table alone.
Repeat any trace that differs by more than 10 percent before writing it down.

Numbers from a feline nerve study are only as good as the three conditions attached to them, and any clinic that reports a velocity without a temperature is reporting a guess with a decimal point.

Terms mentioned in this article

Frequently asked

Why does my cat's nerve report show two very different speeds?

Because one nerve contains several fiber classes at once. The fast peak at 50 to 120 m/s comes from large myelinated motor and proprioceptive axons, while the slow tail near 0.5 to 2 m/s comes from unmyelinated C fibers carrying pain and temperature. A report that averages them into a single number hides exactly the change a neurologist is looking for.

Can a cold room really change the result that much?

Yes. Conduction velocity falls about 1.5 to 2.5 m/s for every degree below 37 C, so a limb left exposed at 22 C for 20 minutes can lose 6 to 10 m/s. That is enough to push a normal cat under 40 m/s and be read as demyelination. Ask whether the limb was warmed and whether the temperature was written on the report.

Does a slow velocity mean my cat has a nerve disease?

Not on its own. Body size, age, limb, and technique move the number by 5 to 10 m/s before any disease is involved, and mild slowing after 8 years is common. A diagnosis needs a warm limb, a side-to-side difference above 10 percent, a matching amplitude change, and clinical signs such as knuckling or dragging.