Electromyography

Question 1

What is EMG?

Answer 1

recording action potentials in skeletal muscle fibres - visual representation of electrical events in muscle
non invasive
EXTRACELLULAR
- both electrodes outside fibres to measure V between 2 sites
- ECG (heart - on limbs/chest)
- EEG (brain - on scalp)

INTRACELLULAR
fine electrodes inserted into cultured cells
one electrode inside, one outside to measure V between inside and outside cell

Question 2

What nerve supplies skin of hand and muscles in hand?

Answer 2

ulnar nerve behind humerus to adductor pollicis

Question 3

What is the consequence of stimulation of the nerve?

Answer 3

sensory and motor inputs affected

so sense stimulation and twitching via motor efferents

Question 4

What if no result from EMG?

Answer 4

wrong positioning

can usually feel sensation first (sensory) and motor later (twitch)

Question 5

What is the effects of increasing frequency of consecutive stimuli?

Answer 5

mild: force disappears before next stimulus, individual twitches
increased: at rate quicker than force takes to dissapear - adds up SUMMATION

very increased: fused or tetanic contraction
no individual twitches seen
so close together
many individual twitched close together - muscle contracts

Question 6

Holding bare wire?

Answer 6

muscle stimulated at frequency higher than needed to cause tetanic contraction

muscles stay contracted –> not for survival –> death

Question 7

How to stimulate highest fused contraction?

Answer 7

voluntarily activating nerves
or in tetanus

recreate maximum smooth force by causing APs to go down nerve >20 impulses/sec