Lab 4 - Neurophysiology in humans

Question 1

TRUE or FALSE - A single muscle fibre may be activated by more than one motor neuron?

Answer 1

FALSE

Question 2

What are the physiological processes that generate EMG waves?

Answer 2

Recording of electrical activity generated at skeletal muscle (currents flowing along the sarcolemma)

Question 3

How do the electrical events that generate EMG relate to the mechanical events which generate twitches?

Answer 3

Electrical events are local depolarisation of the sarcolemma and the action propagating down the t-tubules. this, in turn, released Ca2+ which causes the formation of cross-bridge cycles, generating a twitch.

Question 4

What factors determine conduction velocity in axons?

Answer 4

• myelination

- diameter

Question 5

What factors determine the latency of the T-reflex in the soleus muscle?

Answer 5

• path length
• axon myelination
• axon diameter

Question 6

How is conduction velocity affected by diabetes ?

Answer 6

conduction velocity is reduced. This is possibly due to hyperglycaemia, which alters K+/Na+ATPase activity, causes inflammation and myelin abnormalities.

Question 7

Would Diabetes affect the stretch reflex?

Answer 7

Yes, it will be reduced. this is due to fewer sensory neurons and motor units being activated, as well as longer latency. This is the result of nerve damage and myelination abnormalities.

Question 8

What is an M-wave?

Answer 8

Measured amplitude of a motor unit’s direct response

Question 9

What is an H-wave?

Answer 9

Measured amplitude of a motor unit’s reflex response

Question 10

What happens as voltage is increased when stimulating the soleus? (in regarding to M- and H-waves)

Answer 10

Threshold voltage: Motor neurons are activated via a reflex circuit by direct stimulation of sensory axons. H-waves begin to appear.
Increasing voltage: As motor neurons begin to be directly activated, M-waves begin to appear. The H-wave amplitude also increases as more sensory axons are stimulated, which recruit more motor neurons through the reflex pathway.
Maximum voltage: M-waves are at max amplitude when all the motor neurons are directly activated. H-waves amplitude disappear, as all the motor neurons are already activated directly and are in their refractory period.

Question 11

What effect does diabetes have on a patient’s M- and H-waves?

Answer 11

Lower amplitude and longer lantecy, due to nerve damage and myelination abnormalities.