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electroneurography nerve conduction velocity peripheral neuropathy electrophysiology neurophysiology
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ELECTRONEUROGRAPHYElectrophysiological Principals involved
And
Clinical Diagnosis
Presented by :
SARA SIDDIQUI
Course no. 656
ELECTRONEUROGRAPHY:
Electroneurography is a non invasive, electro neurological diagnostic test to measure the conduction velocity and latency of peripheral nerves.
It is the most accurate test for detecting and locating peripheral nerve injury of about 100 kinds of peripheral neuropathies.
Such as Diabetic polyneuropathy, Gullain-Barre syndrome, Carpel tunnel syndrome, thoracic outlet syndrome
Working Principal:
Conduction velocity is the rate of propagation of nerve impulse (action potential) along a nerve fiber.
NCV determine the distance covered by AP per unit time, NCV = lambda /time
Factors affecting NCV:
1. Diameter of the axon
Different peripheral nerve fibers have different diameters and thus conduction velocity of their own. AP recorded are Compound AP.
2: MYELINATION:
Myelination induces insulation around the fiber except small points known as nodes of Ranvier
Thereby increases resistance across membrane Rm but decreases its capacitance Cm
AP are saltatory in nature
Other Factors
Temperature as proportional to velocity External resistance Rl Density of gates Ions concentrations Anesthetics Anoxia
HOW THE TEST IS PERFORMED STRONG BUT BRIEF STIMULATION AT ONE POINT UNDER THE
SKIN AND AT THE SAME TIME RECORDING THE ELECTRICAL ACTIVITY AT ANOTHER POINT OF NERVE TRAJECTORY IN THE BODY.
The response is displayed on the video monitor of computer or cathode ray tube.
The stimulus and recordings are carried out by the surface or disc electrodes which are placed over the skin after applying the conducting gel.
Stimulus is felt as the electrical shock thus may be painful.
Thoracic Outlet Syndrome
Observations And Diagnosis:
Sometimes EMG is combined with ENoG for accurate diagnosis called as electromyoneurography
Any decrease in the NCV will indicate:
1.Extent of demyelination of nerve
2. Any Conduction Block
3.Axonopathy (damage to the long
portion of a nerve cell)
CLASSIFICATION OF PERIPHERAL NEUROPATHIES:
References:
Neurophysiology:
3rdedition by R.H.Carpenter
Nerve Conduction studies: https://backyardbrains.com/experiments/com
paringNerveSpeed https://Hmphysiology.blogspot.com
peripheral neuropathy: Physical medicine and rehabilitation Board
review – Sara Cuccuvullo MD
For Further Reading:
http://openwetware.org/wiki/Lab_9:_Conduction_Velocity_of_Nerves
http://www.neurolist.com/site/emg_case.htm
Happy Reading !