electro EMG studies

EMG can identify the orign of the weakness such as

- muscle

- nerve (fiber types, pathology, temporal course)

- NMJ

cell body location of sensory vs motor neurons

- sensory: DRG (outside CNS)

- motor: anterior horn cell (inside CNS)

dendrite function

carry impulses to cell body from other neurons

axon function

carry impulses to other sites

what is the function of myelin

helps nerves propagate an AP faster

- myelin sheath functions as insulator of the axon

conduction velocity is directly related to

internodal length and efficiency of myelin insulation

demyelination results from

**loss or dysfunction of the myelin sheath

-usually seen most often in entrapment or compressive neuropathies

- may also occur with some genetic conditions (Charcot-Marie-Tooth), some toxic (diphtheria), or from a immunologic attack on the myelin (GBS)

axonal loss may be seen after

- physical disruption of the nerve or as a result of numerous toxic, metabolic, or genetic conditions that can damage the metabolic machinery of the axon

what is worse: demyelination or axonal loss?

axonal loss

epineurium vs perineurium vs endonerium

- epi: outer covering of the nerve

- peri: covering of the nerve fascicle

- endo: protective cover of individual nerve fibers

what happens at the neuromuscular junction

- When the nerve impulse reaches the axon terminals, ACH is released and diffuses across the synaptic cleft

- if enough ACH is released, the cell becomes excited, therefore an action potential occurs

- The action potential causes muscle contraction

what diseases are associated with neuromuscular junction problems?

- Botulism

- Myasthenia Gravis

why refer for EDX

- problems in the nerves or muscle physiology can be objectively measured electrically

- Peripheral nerve injury can be localized or generalized

- estimate the severity of the injury

- detect injury progression or regression

- aide in establishing appropriate treatment plan

- identify other causes or factors

what abnormal findings from a neuromotor screen suggest using EDX?

- weakness

- parathesias

- altered MSRs

- pain/myalgia/fatigue

- gait/balance disorders

- cramps/fasciculations

_____ → time from stimulation to muscle response (speed of response); measured in mseconds

latency

what is delayed latency?

the "O" (onset latency) appears later than usual

_____ → number of activated muscle/nerve fibers or size of response; measured in millivolts (CMAP) or microvolts (SNAP)

amplitude

if there is decreased amplitude what may be the problem

myonal or axonal injury (anterior horn cell body or axon, Schwann cells, NMJ, or muscle itself)

what is the conduction velocity

how fast the action potential moves down the axon (m/sec)

the CMAP represents

the summation of all the underlying muscle fiber AP

- corresponds to the integrity of the motor unit

since the cell body of motor nerves is located in the anterior horn of the SC, the motor nerve conduction is abnormal in both

preganglionic and postganglionic injuries

the SNAP (sensory nerve action potential) represents the

summation of all the underlying sensory fiber action potentials

t/f: the sensory nerve will always be normal in nerve root problems

true - DRG is not affected (preganglionic)

peripheral sensory nerve testing allows differentiate between

- preganglionic disorders (radiculopathies, cauda equina lesions) and

- postganglionic disorders (neuropathies, plexopathies)

EMG spontaneous muscle activity

electrical activity present when the muscle is at rest and the electrode is not being moved

normal muscle should be ____ after the needle is inserted

silent (unless inserted near NMJ/endplate)

- abnormal: positive sharp waves (PSWs) or fibrillation potentials

fibrillations result from

motor axonal loss that is not balanced by reinnervation

- low amp: occured in the pasy

- high amp: ongoing

EMG insertional activity

the electrical activity present as the electrode is passed through muscle cells

insertional activity may be increased by

conditions causing membrane instability such as neuropathies, radiculopathies, and inflammatory myopathies

what is MUAP

looking at one motor unit & recording voluntary recruitment of motor unit AP

if there is a giant polyphasic motor unit potential what caused this?

collateral sprouting for nerve healing

reduced vs increased recruitment

- reduced: motor axonal loss due to focal demyelination or conduction block

- increased: myopathy