Nerve Conduction Studies Flashcards
Where does electric current flow?
Between two poles
What is the role of the cathode? The anode?
Cathode = depolarizes the nerve Anode = hyperpolarizes tissue in the area
What is the goal to stimulation?
- to create a sudden and rapid alteration in the resting membrane potential of the nerve being evaluated
- bring all axons of that nerve to threshold
Why is a supramaximal stimulus needed?
- provides reproducible results
- it’s representative of the capabilities of that peripheral nerve
What type of axons allow current to flow most easily?
Large-diameter axons, they have a lower resistance
Which axons reach threshold easiest?
smaller cell bodies and smaller axons
During voluntary contraction, what is the recruiting order?
small (type I/slow twitch) to large
During an externally applied current, what is the recruiting order?
Large to small
-current flows down the path of least resistance
How do you know that a supramaximal stimulation was used?
If the stimulus intensity is increased and the compound AP does not get larger with higher levels of stimulus, a supramaximal stimulation is achieved
What ways does the stimulation level vary from patient to patient?
Skin thickness, adipose tissue, connective tissue, musculature
What is a NCS used for?
use to evaluate the function of the motor and sensory nerves of the human body
What is the common measurement made during a NCS test?
nerve conduction velocity (NCV)
What are the 2 main things that NCS evaluates?
paresthesia and/or weakness of the arms and legs
What are some indications for NCS?
- symptoms indicative of nerve damage (numbness, weakness)
- differentiation between local or diffuse disease process (mononeuropathy or polyneuropathy)
- get prognostic information on the type and extent of nerve injury
Examples of peripheral neuropathy
mononeuropathy (carpal tunnel) mononeuritis multiplex (vasculitides, RA, SLE, sacroidosis, leprosy, Lyme disease, amyloidosis) Polyneuropathy (diabetic neuropathy)
Examples of myopathy
muscular dystrophies
myotonia
congenital myopathies
metabolic myopathies
What can cause radiculopathy?
Nerve damage from herniated discs
Give an example of a disease of the NMJ
Myasthenia gravis
NCS are used to determine what 2 things?
1) nerve conduction velocity
2) size of the collective AP
What can NCS evaluate the function of?
peripheral nerves, NMJ, collective muscle fibers innervated by the nerve being examined