Lecture 2

Question 1

Rheobase definition:

Answer 1

The amount of current that needs to be injected into a MN to generate an AP

Question 2

Muscle force is controlled in two ways:

Answer 2

1. Recruitment- Recruit more motor units
2. Rate coding- Make the ones that are active fire more often

Question 3

Henneman’s size principle:

Answer 3

Orderly recruitment is due to variations in motor neuron cell body size

Question 4

What size motor neurons are recruited first according to Henneman’s size principle?

Answer 4

Smaller motor neurons

Question 5

What observation did Denny-Brown (1938) make with respect to performance of movement?

Answer 5

Performance of a particular movement always appears to be accomplished by the activation of motor units in a set sequence

Question 6

Positive effects of recruitment of MUs in an orderly fashion:

Answer 6

• Sequence is predetermined
• Brain only needs to control the level of the input to the motor pool
• Adding larger MUs near the end of a contraction when incremental increase will have a substantial effect on net force
• Fine motor control

Question 7

Negative effects of recruitment of MUs in an orderly fashion:

Answer 7

• Inability to selectively activate motor units out of order
• Limited in the rate of force development

Question 8

Twitch definition:

Answer 8

The physiological response of a motor unit to a single stimulation

Question 9

Different twitch profiles per motor unit type:

Answer 9

FG: Fast twitch- Glycolytic
FOG: Fast twitch- oxidative/glycolytic
SO: Slow twitch- oxidative

Question 10

Latent period definition:

Answer 10

Represents time between AP and onset of torque- speed of binding

Question 11

Peak definition:

Answer 11

Measures force which is dependent on the number of crossbridges

Question 12

Contraction phase:

Answer 12

Speed of powerstroke, dependent on cycling rate of myosin (measured by contraction time)

Question 13

Relaxation phase:

Answer 13

Phase based on resequestering of Ca2+ (measured by half relaxation time HrT)

Question 14

Why does fused tetanus generate more force than a single twitch?

Answer 14

The levels of calcium in the sarcoplasm of the skeletal muscle stay higher for longer during a fused tetanic contraction

Question 15

What is a surface EMG?

Answer 15

Uses electrodes adhered to the skin that pick up electrical activity of the muscle underneath (AP down the sarcolemma)

Question 16

What does a surface EMG allow us to see?

Answer 16

What the nervous system is doing non-invasively