EMG

Question 1

what is each individual muscle fibre innervated by ?

Answer 1

Each individual fibre is innervated by a branch of a motor axon

Question 2

what is EMG ?

Answer 2

Electromyography is a technique that measures the electrical activity of the muscles and the nerves controlling the muscles.

Question 3

how does EMG work ?

Answer 3

. electrodes placed on the skin surface
. The size and shape of the waveform measured provide information about the ability of the muscle to respond when the nerves are stimulated.
. The EMG provides a depiction of the timing and pattern of muscle activity during complex movements. The raw surface EMG signal reflects the electrical activity of the muscle fibers active at that time.

Question 4

when is EMG usually used ?

Answer 4

. EMG is most often used when people have symptoms of weakness
. It can help to differentiate muscle weakness caused by neurological disorders from other conditions.

Question 5

what is coactivation ?

Answer 5

a phenomenon in which contraction of a muscle leads to more minor activity in the antagonist muscle.

Question 6

what is the consequence of coactivation ?

Answer 6

The phenomenon of agonist-antagonist muscle coactivation has consequences for movement mechanics such as facilitating faster movements, and effects on action stability and fine movement and joint stability.

Question 7

What units is the amplitude measured in?

Answer 7

mV

Question 8

What happened to the amplitude with increased weight?

Answer 8

As weight increases, amplitude increases.

Question 9

What type of muscle contraction have you been doing when you increase weight?

Answer 9

Voluntary contraction

Question 10

Unlike the discrete waveform from an electrocardiogram, the electromyogram waveform is irregular. Why do you suppose this is?

Answer 10

Unlike, the heart, skeletal muscle does not contract in a fully synchronized fashion. Instead, an EMG is recording the unsynchronized electrical activity of many muscle fibers.

Question 11

How the EMG trace changed when you added weights to your arm ?

Answer 11

The heavier the load, the greater the recorded activity. Greater motor unit activity is required to generate more force.

Question 12

In your own words what is coactivation?

Answer 12

. Muscle is activated in cooridantion with another muscle. Agonist and antagonist.
. Coactivation is a small increase in activity in a non active muscle that is in opposition to a muscle that is contracting forcefully.

Question 13

what is an example of coactivation ?

Answer 13

For Bicep contraction, bicep amplitude is much higher than tricep contraction. A phenomenon in which contraction of a muscle leads to more minor activity in the antagonist muscle.

Question 14

How many muscle fibres are there per motor unit in biceps or triceps?

Answer 14

Larger muscles eg those involved in movement 150-500 muscle fibres.

Question 15

Describe what is occurring in triceps during bicep contraction ?

Answer 15

Triceps relax while biceps contract.

Question 16

what diseases can be detected using EMG ?

Answer 16

Measuring the electrical activity in muscles and nerves can help detect the presence, location and extent of diseases that damage muscle tissue or nerves
e.g. muscular dystrophy or ALS

Question 17

how was evoked EMG tested ?

Answer 17

. You will be stimulating the median nerve at the wrist, and recording the resulting muscle electrical activity from the thumb muscle.

Question 18

What units is latency measured in?

Answer 18

Measured in units of time – seconds, hours or minutes

Question 19

what is latent period?

Answer 19

the time it takes for the muscle to contract in response to the electrical pulse

Question 20

what is the speed of muscle dependent on ?

Answer 20

The speed of the response is dependent on the conduction velocity.
. normal conduction velocities 50 to 60 (m/s).

Question 21

How did the latent period change with an increase in pulse current? why?

Answer 21

Does not change action potentials travels constant speed. But wavelength and amplitude changes.

Question 22

List the physiological events that occur during the latent period ?

Answer 22

1. Initiation of action potential in nerve fibers
2. conduction of the impulse along the nerve
3. transmission at the neuromuscular junction
4. initiation of action potential in muscle fibers.

Question 23

What are the units of nerve conduction velocity?

Answer 23

m/s

Question 24

How fast does an electrical impulse travel through your median nerve (or ulnar nerve)?

Answer 24

50 m/s

Question 25

What disease could slow down nerve conduction velocity and why?

Answer 25

. Carpal tunnel syndrome due to slower conduction velocities may also be caused by injury or damage to a nerve

. Multiple Sclerosis – affects cns, demyelinating disease (attacks myelin sheath).

Question 26

What is voltage?

Answer 26

change in electrical acitivity between 2 points

Question 27

How do you counteract more force?

Answer 27

you must induce more muscle contraction and therefore induce more muscle membrane electrical activity.
The waveforms increase as you add more weight of books- by increasing the amplitude

Question 28

How does the table calculate your nerve conduction velocity?

Answer 28

measure the distance between the wrist and elbow electrode points using a ruler.

Question 29

What is stimulation measured in?

Answer 29

mA- measure of current induced

Question 30

When electrocuting what happens?

Answer 30

inducing one synchronized firing of the action potential on all the neurons o your nerve which will stimulate all of the muscle fibres in one synchronised action. The waveform looks different- one unified event.

Question 31

What is an artefact peak?

Answer 31

muscle/electrical activity in response to a shock

Question 32

What is the latent period in evoked EMG?

Answer 32

time between stimulation and the first upward infliction of your response

Question 33

How can you measure your response in the evoked EMG?

Answer 33

You can measure the amount of response i.e the size of the evoked response - size/shape of the amplitude

Question 34

w

Answer 34

measuring activty in the thumb muscle

stimulus current changes amplitude of wave- amplitude of wave is bigger when you use 20mA stimulation than 10mA.

Question 35

How is the latency period determined in evoked EMG?

Answer 35

by the distance by the electrode on your wrist and electrode in thumb muscle
it is the time taken for the action potential in the neurons to travel from the point of stimulation in the wrist to synapses and induce changes in muscle activity in thumb muscle fibres.

Question 36

What explains the decrease in amplitude of the wave although stimulus current is the same?

Answer 36

the median nerve is deeper in tissue- which means more stimulus is absorbed by connective tissue between skin and nerve.
You will have a decrease in the amplitude in the wave even though you are stimulating with the exact same current- due to less current is able to penetrate through the tissue and stimulate the axons in the nerve.
-There is more electrical insulation from fat tissue between skin and nerve at the wrist.

Question 37

Why does the latency period get longer?

Answer 37

action potential takes longer due to more current being dissipated by the connective tissue.

Question 38

How do you calculate the nerve conduction velocity/ i.e speed of action potential running along with the neuron of the axon of the median nerve?

Answer 38

The latency period between 2 points of stimulation
Take latency period from wrist to thumb and subtract that from the latency period from elbow to thumb. That tells you the time taken for stimulus/a.p to run along the axon.

Question 39

Why could nerve conduction velocity be lower than 50m/s?

Answer 39

-Small axon with small diameter
-Less myelination- demyelinating disease- less electrical insulation, therefore, the signal can not be propagated between nodes of Ranvier slowing down the speed of transmission.
-

Question 40

What is a disease that results in demyelination?

Answer 40

multiple sclerosis