EBM Practical

Question 1

What were the objectives for the first experiment (motor neuron action potential propagation)

Answer 1

To study the velocity at which action potentials propagate along motor neuron axon
To observe the EMG resulting from electrically activating motor neurones in the Ulnar nerve

Question 2

Would you expect the evoked EMG to be larger than the EMG obtained from pushing out your little finger

Answer 2

Yes because in the voluntary contraction each nerve is asynchronously activating the motor neurones whereas the stimulated contraction the nerves are all activated at the same time causing a larger reading due to temporal summation

Question 3

Would you expect the evoked EMG to change polarity when you change the polarity of the stimulus

Answer 3

No because action potentials are mono-directional

Question 4

The artefacts from the 2nd and 3rd were usually not obtained however the 1st were. Why is this

Answer 4

Because the 2nd and 3rd were further away from the recording electrode which makes it harder to pick up the stimulus

Question 5

Why would you not just take the delay distance from any stimulus site to the recording electrodes instead of taking the difference

Answer 5

Measurement errors, when you stimulate nerves there’s other delays eg the time taken to depolarise and also because we want the propagation velocity along the axon

Question 6

Is the propagation velocity calculated the kind of value you would have expected for an alpha motor neuron

Answer 6

Would expect to be 30~60m/s as it conducts quickly due to myelination

Question 7

What were the objectives of experiment 2 (stretch reflex arc)

Answer 7

Observe the EMG results and resulting from the reflex action of the biceps and calf muscle in response to stretching the muscles tendon
Determine the reflex arc involved and estimate the propagation velocity of the action potentials in this reflex arc from the reflex delay and the length of the reflex nerve

Question 8

What determines the amplitude of the recording EMG

Answer 8

The intensity of the stimulus and how may motor units are active at the same time for temporal summation

Question 9

Why is it important the volunteer doesn’t stretch the Achilles’ tendon by pulling the foot upward

Answer 9

Because this will shorten the tendon meaning it will not shorten further. This active contraction will surpress the reflex

Question 10

Why is the voluntary response slow compared to the reflex

Answer 10

Because it takes time for the information to reach the brain as well as other time such as synapsing whereas the reflex is direct

Question 11

Why is the evoked EMG larger than the EMG obtained by tensing the bicep

Answer 11

Because with the reflex there is synchronised activation meaning temporal summation