L11 Skeletal Muscle

Question 1

Modulation of force generation in skeletal muscle

Answer 1

Length/tension relationships

Summation

Motor unit recruitment

Fiber cross-sectional area ( atrophy/hypertrophy)

Fiber type (fast-twitch, slow-twitch)

Question 2

Isometric contraction

Answer 2

Same length

Lift something and just hold it up

Generate force but no appreciable shortening of muscle length (no work )

Question 3

Isotonic contraction

Answer 3

Same tension

Contractions that result in shortening of muscle length against a constant load (work done)

Question 4

Passive tension

Answer 4

Tension developed by simply stretching a muscle (no stimulation)

Question 5

Total tension

Answer 5

Tension developed when a muscle stimulated at different muscle lengths (preload)

Sum of active and passive tensions

Question 6

Active tension

Answer 6

Determined by difference in tension

Active=total -passive

Tells what percentage due to cross bridge formation

Question 7

Peak active tension

Answer 7

Optimal length (Lo)

In vivo is resting length

Max point we can have max amount of cross bridges

Question 8

Maximal tension

Answer 8

Can be developed at optimal length b/c this is the point of optional thin and thick filament cross bridge binding sites

Question 9

What’s resting SKELETAL muscle length near in the body?

Answer 9

Lo optimal length !

Question 10

Single muscle twitch

Answer 10

A single action potential in a muscle fiber produces a brief, weak contraction

Question 11

Frequency of stimulation influences the

Answer 11

Tension developed by each fiber

Question 12

Whats Twitch summation and what does it result from ?

Answer 12

Muscle fiber and re-stimulated before it completely relaxed

A sustained elevation in cytosolic Ca

Question 13

Tetanus

Answer 13

Muscle fiber stimulated so rapidly it does not have an opportunity to relax at all

Maximal sustained contraction

Question 14

Motor unit

Answer 14

Motor neuron and innervated fibers

All fibers in a motor unit contract “all or none”

Question 15

What do muscle fibers are into?

What do they produce?

Answer 15

Whole muscles

produce contractions of variable grades -“graded activation”

Question 16

What does graded force development within a whole

Muscle depend on ?

Answer 16

Extent of motor unit recruitment

Little force- recruit small, slow motor units

Greater force- recruit large, fast motor units

Question 17

Muscle fiber types in humans

Answer 17

Myosin type I

Myosin type IIa

Myosin type IIx

Fiber type proportion varies among muscles

Question 18

One motor unit always has

Answer 18

The same fiber types!

Question 19

Type I

Answer 19

Slow-twitch (more oxidative, more mitochondria)

Fatigue slowly

Red in color

Supplied with capillaries

Twitch tension low

Question 20

Type IIx

Answer 20

Fast twitch (fast oxidative , more dependent on glycolysis)

Fatigue rapidly

Larger diameter

High glycogen content

White

Tension twitch high

Question 21

Type IIa

Answer 21

Fast twitch (oxidative/glycolysis)

Low resistance to fatigue

Intermediate color

Tension twitch moderate

Question 22

Order of resistance to fatigue of muscle fiber types

Answer 22

I>IIa>IIx

Question 23

Which muscle fiber type is recruited first?

Answer 23

Type I and small motor units

Question 24

Average persons fiber types

Answer 24

Mostly slow type I

Smaller amount type IIa

Even smaller amount type IIx

Question 25

As endurance based athleticism increases how do muscle fiber types change?

Answer 25

Slow type I increases Type IIa and IIx decrease

Question 26

How do muscle fibers change in sprinters and sedentary people change?

Answer 26

Fast type IIx increases Slow type I and fast type IIa decrease

Question 27

An extreme endurance athlete has which muscle fibers?

Answer 27

Almost all slow type I Very small amount type IIa

Question 28

A person with small cord injury has what ratio of muscle fibers?

Answer 28

Almost none of slow type I Equal ratio of fast types IIa and IIx