Electromyography

Question 1

What does EMG record?

Answer 1

Changes in electrical potential of a muscle when contracted via motor nerve impulse.

Question 2

What is a motor action potential (MAP)?

Answer 2

Action potential that spreads across a single muscle fibre

Question 3

What is a motor unit action potential (MUAP)?

Answer 3

Summation of motor action potentials from fibres of a given motor unit.

Question 4

What is a motor unit action potential train (MUAPT)?

Answer 4

A sequence of motor unit action potentials as a result of repeated neaural stimulation.

Question 5

What is a physiological EMG signal?

Answer 5

Sum of motor unit action potential trains across multiple motor units.

Question 6

Why is a physiological EMG signal never recorded?

Answer 6

Because passage of signals through tissues distorts signal - acts as a low pass filter eliminating some high frequency noise.

Question 7

What are the experimental procedures for EMG?

Answer 7

Electrode area shaved
Cleaned using alcohol wipe
A raised using sandpaper
Wiped clean again
Two electrodes applied in centre of muscle belly parallel to fibre direction.

Question 8

How is EMG data processed?

Answer 8

EMG measures polarisation and depolarisation of muscle fibres so traces must be rectified first
Average produced
Smoothed using low pass and high pass filters witheliminate high and low frequency noise respectively.