Basics Behind Nerve Conduction Studies Flashcards
What happens to the nerve underneath the cathode?
it depolarizes
What happens to the tissue in the area of the anode?
it hyperpolarizes
What is the goal of electrical stimulation?
To create a sudden and rapid alteration in the resting membrane potential of the nerve being evaluated
In a voluntary contraction a supramaximal stimulus is needed for what reasons?
Reproducible results
What does the response generated from a voluntary contraction represent?
the capabilities of that peripheral nerve
Current flows most easily through _____-diameter axons due to what?
large
due to low resistance
What type of nerves will reach threshold faster? Why?
Smaller cell bodies and smaller axons will reach threshold easier because they have a higher resistance
What type of muscle fibers are activated first during a voluntary contraction?
Small, slow-twitch, type I muscle fibers
In what direction does current flow with an externally applied current?
Down the paths of least resistance, so from larger-diameter axons to the smallest
In an externally applied current a supramaximal stimulus is needed for what reasons?
In order to fully activate the peripheral nerve
What does the response generated from an electrically applied stimulus represent?
The capabilities of all axons associated with a given nerve
How is an electrically stimulated supramaximal stimulation verified?
By increasing the stimulus intensity until the compound action potential does not get larger with higher levels of stimulus
This stimulus level will vary from patient to patient, depending upon what 4 things?
- Skin thickness
- Adipose tissue
- Connective tissue
- Musculature
What is a nerve conduction study?
a test commonly used to evaluate the function of the motor and sensory nerves of the human body
What are nerve conduction studies mainly used for?
Evaluation of paresthesias and/or weakness of the arms and legs
What are 3 indications for a nerve conduction study?
- Symptoms indicative of nerve damage, such as numbness and/or weakness
- Differentiation between local or diffuse disease process (mononeuropathy or polyneuropathy)
- Get prognostic information on the type and extent of nerve injury
What are 4 common disorders diagnosed by NCS?
- Peripheral neuropathy
- Myopathy
- Radiculopathy
- Diseases of neuromuscular junction
What are 3 types of peripheral neuropathies?
- Mononeuropathy
- Mononeuritis multiplex
- Polyneuropathy (ex: diabetic neuropathy,)
What is an example of mononeuropathy?
carpal tunnel syndrome
What are a couple examples of mononeuritis multiplex?
- vasculitides
- RA
- SLE
- sarcoidosis
- leprosy
- Lyme disease
- amyloidosis
What are 4 common types of myopathies diagnosed via NCS?
- Muscular dystrophies
- Myotonia
- Congenital myopathies
- Metabolic myopathies
What is a common disease of the neuromuscular junction?
Myasthenia gravis
What are the 2 things NCS are used to determine?
- Nerve conduction velocity (speed of conduction)
- Size (amplitude) of the collective action potential
NCS evaluate the function of what 3 things?
- Peripheral nerves
- The N/M junction
- The collective muscle fibers innervated by the nerve being examined
Does a NCS involve a puncture of the skin?
No
What does an electromyography (EMG) evaluate?
The electrical activity of the muscles and the muscle APs monitored from a sample of muscle fibers