Muscles And Motor Units

Question 1

Describe the chain of events in muscle contraction

Answer 1

1.action potential stimulates the real ease of a neurotransmitter across the neuromuscular junction
2.AP spreads across muscle membrane and into fibre along T tubules
3.cause release of calcium from sarcoplasmic reticulum
4.calcium binds to muscle and causes cross bridge cycling

Question 2

What is twitch fusion and motor unit recruitment

Answer 2

Continuous smooth muscle contraction is generated by the fusion of multiple twitches.

Question 3

How do muscles generate extra force

Answer 3

1.recruit more motor units
2.increasing the frequency of firing

Question 4

Movement precision determined by number of motor units:

Answer 4

Muscles differ greatly in both numbers of fibres and number of motor neurons.

Innervation number=fibres/motor neurons

Lower innervation number=more control

Question 5

How do we measure muscle activity

Answer 5

We use a technique called electromyograpgy (emg)

Question 6

Compared with slow muscle fibres fast fibres have:

Answer 6

Higher resting membrane potentials

Greater density of sodium

Faster action potentials

Thus fast fibres generate larger electrical responses

Question 7

Emg/force relationship depends on joint angle

Answer 7

Quadriceps emg force relationship changes at different knee angles

Question 8

What happens in changes in fusion frequency after fatigue

Answer 8

Muscle fatigue causes prolonged twitch duration due to biochemical changes in the muscle

Question 9

How does the nervous system know when to reduce motor neurone firing rate

Answer 9

1.peripheral detection the build of metabolites and pain via receptors
2.spinal suppression of motor neurone firing rates
3.changes in voluntary activation

Question 10

Why does the nervous system reduce firing rate

Answer 10

1.to reduce the likelihood of neuronal fatigue
2.more likely to maintain muscle control (if firing rate is way above fusion frequency for modulation is limited)

Question 11

Describe high frequency fatigue

Answer 11

1.only occurs artificially
2.caused by continous high frequency stimulation
3.normally prevented by muscle wisdom

Question 12

Describe low frequency fatigue

Answer 12

1.occurs after mild muscle damage
2.need to activate muscle at higher frequency to get same force
3.takes hours/ days to recover
4.causes probabky by reduced calcium from the sarcoplasmic reticulum due to mechanical damage

Question 13

What causes loss of force during a fatiguing contraction

Answer 13

Mainly caused by biochemical changes in the muscle itself

Question 14

What is twitch interpolation

Answer 14

Abstract. An electrical stimulus delivered to a muscle nerve during a maximal voluntary contraction usually produces a twitchlike increment in force. The amplitude of this “interpolated twitch” is widely used to measure voluntary “activation” of muscles.

Question 15

Describe muscle stimulation during fatigue

Answer 15

1.as fatigue develops stimulation produces greater twitch force

2.evidence that neural drive to the muscle is reduced-central fatigue

Question 16

Describe motor cortex stimulation during fatigue

Answer 16

Generate more twitch force at the end of a contraction compared to the beginning suggesting the brain is not driving the motor cortex as much as it could