Electromyography

Question 1

What is an EMG (electromyography)

Answer 1

Recording of AP occurring in skeletal muscle fibres using extra-cellular recording outside fibres to record the potential between two locations

Question 2

What happens in an intracellular EMG recording

Answer 2

One electrode inside cell
One outside
Measuring voltage between inside an outside of cels

Question 3

What happens in an extracellular EMG recording

Answer 3

Both electrodes outside the muscle fibres, measuring voltage between two sites outside the cells

Question 4

What happens at the first and second electrode in an EMG?

Answer 4

Peak at first electrode causes voltage deflection
propagation is between at zero
Peak at second electrode causes an opposite voltage deflection

Question 5

What does a transducer do?

Answer 5

Converts force to electrical signal

Question 6

What is seen on an EMG in response to a voluntary contraction?

Answer 6

As force exerted by muscle increases, EMG amplitude on recording increases

Question 7

What does a stronger artificial stimulus do to EMG?

Answer 7

Leads to action potentials and a stronger/larger twitch

Question 8

What does increasing frequency of stimulus do to EMG?

Answer 8

Leads to more homogenous output without distinct outputs. Summating output to produce one larger force

Question 9

What is tetanus?

Answer 9

Contraction where twitches are so rapid that they produce a fused tetanic contraction without distinct contractions

Question 10

What happens in an electric shock?

Answer 10

If 50Hz mains,
muscles undergo tetanic contraction
Can’t let go because of muscles clamping