16 - Controlling Contractions

Question 1

What are the 2 aspects to delay in axon conduction velocity?

Answer 1

• conduction/latency

- delay in NMJ

Question 2

Conduction/latency

Answer 2

Time taken for AP to travel from point of stimulation to NMJ

Question 3

Delay in NMJ

Answer 3

Process by which ACh vesicles fuse w/ membrane, release and bind to post-synaptic receptors

Question 4

What’s the motor end plate?

Answer 4

Post-synaptic region of NMJ

Question 5

Why is Ca2+ only briefly available in the intracellular space of muscle cell?

Answer 5

When Ca2+ floods out of SR, it’s simultaneously being actively pumped back into SR by Ca2+-ATPase

Question 6

What has to be available for cross-bridge cycling to occur?

Answer 6

Ca2+ and ATP

Question 7

When does cross-bridge cycling stop?

Answer 7

When all Ca2+ pumped back into SR

Question 8

What does Ca2+ limit?

Answer 8

Duration of cross-bridge cycling

Question 9

What does ATP limit?

Answer 9

How quickly cross-bridge cycling occurs (more ATP = faster)

Question 10

Sliding filament theory

Answer 10

Myosin heads marching along actin, pulling Z discs towards centre of sarcomere

Question 11

Latent period

Answer 11

Before force generation

Question 12

Contraction period

Answer 12

Force always increasing and Ca2+ binding to troponin, revealing actin binding sites

Question 13

Relaxation period

Answer 13

All Ca2+ pumped back into SR

Question 14

What are 2 reasons for latent period?

Answer 14

• takes time for AP to be conducted to muscle

- additional latent period after release of ACh reflects Ca2+ release from SR

Question 15

What limits maximum force generation?

Answer 15

• takes time for cross-bridge binding to occur

- passive muscle tension

Question 16

If 2nd stimulation occurs during contraction period…

Answer 16

Force will smoothly summate but if arrives during relaxation period, unfused tetanus occurs

Question 17

Titin filaments

Answer 17

3rd protein filament integrated into sarcomeres

Somewhat elastic and accounts for passive muscle tension

Question 18

Optimal length

Answer 18

Dependent on optimal overlap of actin and myosin

Question 19

Maximum length

Answer 19

No overlap of actin and myosin

Question 20

Minimum length limited by

Answer 20

Thin filament overlap

overlap of this filaments and Z discs

Question 21

Isotonic contractions

Answer 21

Muscle changes length while maintaining constant tension

Question 22

Isometric contractions

Answer 22

Muscle develops tension without changing length

Question 23

Time-course of force generation in isometric contraction

Answer 23

• force generation begins from time of first cross-bridge attachment
• total duration depends on sequestration of Ca2+ by SR

Question 24

Time-course of force generation in isotonic contraction

Answer 24

• evidence of shortening delayed until enough cross-bridges have attached to counteract load
• shortening ends once load returns to resting position

Question 25

Concentric muscle contraction

Answer 25

Bicep muscle shortening while contracting

Question 26

Eccentric muscle contraction

Answer 26

Bicep muscle lengthening while contracting

Question 27

Concentric

Answer 27

After power stroke, myosin head progressively binds further along actin, leading to shortening

Question 28

Eccentric

Answer 28

External force applied to muscle means it lengthens even as power strokes occur

Question 29

How are types of skeletal muscle fibre defined?

Answer 29

1. Max shortening velocity | 2. ATP pathway

Question 30

Max shortening velocity

Answer 30

Type 1 - slow; low ATPase activity | Type 2 - fast; high ATPase activity

Question 31

What does ATPase activity affect?

Answer 31

Max rate of cross bridge cycling

Question 32

ATP pathway

Answer 32

A) oxidative - depend on oxygen (numerous mitochondria, good blood supply, lots of myoglobin, red) B) glycolysis - large glycogen stores(thicker, greater tension development, white)

Question 33

What are the 3 fibre types?

Answer 33

1a - slow oxidative 2a - fast oxidative 2b - fast glycolytic

Question 34

T/F muscle fibres in single muscle unit are different types

Answer 34

False - same type

Question 35

If experimentally change type of AP stimulation, can change type of...

Answer 35

Muscle fibre that it appears to be

Question 36

Type 1 fibres have motor units that

Answer 36

Have smaller cell bodies and smaller diameter axons | Produce steady, low freq activity

Question 37

Type II fibres have motor units that

Answer 37

Have larger cell bodies and larger diameter axons | Produce occasional high freq bursts

Question 38

T/F small units are recruited last

Answer 38

False - recruited first

Question 39

Forcing slow motor neurons to innervate fast-twitch muscles causes a change in...

Answer 39

Muscle fibre phenotype

Question 40

What have chronic low freq stimulation experiments shown?

Answer 40

Pattern and type of APs coming in to a fibre determine fibre’s type