Muscle electrophysiology (Practical)

Question 1

What is the purpose of the isolated stimulator?

Answer 1

Prevents mains voltages from being conducted through subject

Question 2

What are the coloured sockets associated with the stimulating/indifferent electrodes?

Answer 2

1. Red socket = Indifferent electrode (metal plate + rubbers strap)
2. Black socket = Stimulating electrode (steel ball)

Question 3

What is the maximum current that should be used to stimulate muscle?

Answer 3

20 mA

Question 4

How can the conduction velocity be determined by measuring latency of muscle response?

Answer 4

• Latency plotted against distance from the measuring electrodes
• Gradient of graph is the velocity

Question 5

What is the Jendrassik manouvevre?

Answer 5

Clasping hand together and pulling hard

Question 6

What are the effects of the Jendrassik manoeuvre on tendon reflex?

Answer 6

Enhances it

Question 7

What is the Hoffmann reflex?

Answer 7

Direct stimulation of nerve innnervating muscle causes 2 separate contractions, M-wave and H-wave

Question 8

What causes the different waves in the Hoffmann reflex?

Answer 8

1. M-wave: Muscle contraction due to stimulation of motor neurones
2. H-wave: Muscle contraction due to stimulation of afferent sensory neurones that trigger monosynaptic stretch reflex

Question 9

What is full-wave rectification?

Answer 9

Adding negative peaks to positive peaks in bipolar electrode recording

Question 10

What are the 2 waves corresponding to the hand-stretch reflex?

Answer 10

M1: Stretch reflex mediated at spinal cord level

M2: Stretch reflex mediated by cerebral cortex via pyramidal tract

Question 11

What does use of physiotherapy vibrator on triceps demonstrate?

Answer 11

• Vibrator stimulates muscle spindles in the triceps
• This causes disruptions in proprioception