A nerve conduction study (NCS) evaluates the function of motor and sensory nerves by measuring nerve conduction velocity, latency, and amplitude. Key components of an NCS include motor nerve conduction studies, F-wave responses, sensory nerve conduction studies, H-reflexes, and repetitive stimulation tests. NCS provides information about nerve demyelination, axonal injury, and other neuropathies.

1. WHAT IS NCS ?
 A nerve conduction study (NCS) : is a test used to
evaluate/ detect the function of motor and sensory
nerves of the human body.
 Nerve conduction velocity (NCV): is a common
measurement made during this test.

2.  The nerve conduction studies most commonly
performed are compound muscle action potentials
(CMAPs) for motor nerves, sensory nerve action
potentials (SNAPs) for sensory nerves, compound
nerve action potentials (CNAPs) for mixed (sensory
and motor) nerves and late responses (primarily F-
waves and H-reflexes).

6. Components :
 MNCS
 F WAVE RESPONSE
 SNCS
 H REFLEX
 REPETITIVE STIMULUS TEST-decrement
 EVOKED POTENTIALS
 SSEP
 VEP
 BAEP

7. NCS
 Latency  Latency – time interval between the
 Velocity onset of a stimulus and the onset of a
 amplitude response (can also be referred to as a
motor latency or a sensory latency).
 Amplitude – the maximal height of
the action potential.
 Conduction velocity – how fast the
fastest part of the impulse travels (can
also be referred to as a motor
conduction velocity or a sensory
conduction velocity).

8. NORMAL VALUES
LATENCY AMPLITUDE VELOCITY
UL
MOTOR N. < 4.0 ms 5-10 mV 50-60m/s
SENSORY N. <3.2-3.4 ms 5-50 µV 50m/s
LL
MOTOR N. <5.2ms 2-10mV 40-50m/s
SENSORY N. <3.5-4.0 ms 5-40µV 35-40m/s

9. CMAP

11. ELECTRODE PLACEMENT
 ACTIVE ELECTRODE : placed on the motor point of
the muscle
 REFERENCE ELECTRODE : placed nearby tendon or
bone
 GROUND ELECTRODE : in between active and
reference electrode

13. B. DISK ELECTRODE
A. GROUND ELECTRODE
C. RING ELECTRODE

14. DIRECTION OF CONDUCTION
 Orthodromic conduction
 Antidromic conduction
 Orthodromic – when the electrical impulse travels in
the same direction as normal physiologic conduction
(e.g., when a motor nerve electrical impulse is
transmitted toward the muscle and away from the
spine or a sensory impulse travels toward the spine).
 Antidromic – when the electrical impulse travels in the
opposite direction of normal physiologic conduction
(e.g., conduction of a motor nerve electrical impulse
away from the muscle and toward the spine).

17. M-WAVE
 Orthodromically stimulated motor response known
as CMAP
 Supramaximal stimulus
 MNCV =
distance between 2 stimulus sites
difference between 2 latency

21.  USES :
 When all motor fibers undergo Demyelination
 long latency
 Slow NCV
 Partial demyelination
 Normal latency and velocity
 Reduced amplitude
 Well marked demyelination
 Absence of conduction
 Axonal degeneration
 Reduced amplitude
 Neuropraxia
 Distal to the lesion – normal NCV
 Proximal to the lesion – reduced conduction velocity

22. F-WAVE
A compound muscle action potential evoked by
antidromically stimulating a motor nerve from a
muscle using maximal electrical stimulus. It
represents the time required for a stimulus to travel
antidromically toward the spinal cord and return
orthodromically to the muscle along a very small
percentage of the fibers

23.  F wave latency :
median nerve – 22.34 ms
ulnar nerve – 23.32ms
peroneal nerve – 40.56ms
tibial nerve – 38.58ms

24. F –wave latency in GBS

25.  USES :
 A prolonged asymmetric F waves suggest a proximal root lesion.
 Clinical application best for plexopathy.
 Quite prolonged in demyelination and mild prolongation in
axonal injury.
 Assesses proximal neuropathology
 Eg:
 GBS
 Thoracic outlet syndrome
 Charcot’s Mary-tooth disease
 proximal nerve entrapment

26. SNCV
 It is performed by electrical stimulation of a peripheral
nerve and recording from a purely sensory portion of
the nerve, such as on a finger.
 14 cm standard distance is used
 Threshold level stimulus is required
 sensory latencies are on the scale of milliseconds(ms).
 sensory amplitude are on microvolt range.
 2 TYPES :
 ORTHODROMIC TESTS
 ANTIDROMIC TESTS

27. An Idealized Sensory Waveform
S = Stimulus point, T = Takeoff point, P = Peak
The time (latency) from S to T is typically about 3 milliseconds.
The amplitude would be measured in microvolts (μV).

29. H-REFLEX
A compound muscle action
potential evoked by orthodromically
Stimulating sensory fibers, synapsing at the
spinal level and returning Orthodromically
via motor fibers. The response is thought to
be due to a Monosynaptic spinal reflex
(hoffmann reflex) found in normal adults
in the Gastrocnemius-soleus and flexor
carpi radialis muscles.

30. 4. H - REFLEX
 Assesses continuity and function of sensory and
motor monosynaptic pathway of 1st sacral nerve
root
 Submaximal stimulus/LONG LATENCY-
29.8ms
 Disappears during supra maximal stimulus
 H-reflex study uses stimulation of a nerve and
recording the reflex electrical discharge from a
muscle in the limb.

32. H -reflex

33.  Normal latency : 29.8 millisecond
( got long latency)
 Implication : used in the
 diagnosis of S1 and C7 root lesions
 the study of proximal nerve segments in either
peripheral or proximal neuropathies.
 Its absence or abnormal latency on one side strongly
indicates disease

36. REPETITIVE STIMULATION
 Repeated electrical stimulus applied to the motor
neuron at a rate of 3-5 / second , the amplitude of the
recorded muscle response is constant
 Decrement of more than 10% is abnormal
 Supramaximal stimulus
 Used to find NMJ abnormalities
 Eg: myaesthenia gravis
Lambert Eaton syndrome
 MMEP is measured

37. REPETITIVE STIMULATION
A repetitive nerve stimulation study
demonstrating a 61 percent decrement in
area and a 54 percent decrement in
amplitude from the first to the fourth
stimulation.

38. EVOKED POTENTIALS
 Assessing the electrical activity in CNS

39. Modified 10-20 System

40. Evoked Potentials

41. VEP

42. SSEP