Chapter 11

Question 1

How do you “type” a muscle fiber?

Answer 1

1. Myosin ATpase

2. Myosin heavy chain characteristics

Question 2

What are the three fiber types?

Answer 2

Type I
Type IIa
Type IIx

Question 3

What are the most common fiber types?

Answer 3

Type I

Type IIa

Question 4

How abundant are Type IIx in humans?

Answer 4

least abundant

1-2% of fibers in muscle

Question 5

T/F

All muscle fibers in a motor unit are the same type.

Answer 5

True

Question 6

Myosin heavy chain has many ______.

Answer 6

isoforms that represent different types

Question 7

Isoforms?

Answer 7

proteins that have different structures but similar functions

Question 8

What determines the speed of contraction?

Answer 8

Myosin ATPase activity

Question 9

Describe the ATPase activity of Type II fibers?

Answer 9

have high activity can complete cross bridge cycles more rapidly, have faster shortening velocities, and achieve peak tension faster than type I

Question 10

Oxidative capacity?

Answer 10

refers to the capacity for oxidative (aerobic) metabolism

Question 11

Glycolytic capacity?

Answer 11

refers to the capacity for anaerobic metabolism of carbohydrate

Question 12

When does fatigue occur?

Answer 12

hindering of resynthesis of ATP

Question 13

What type has greatest resistance to fatigue? lowest?

Answer 13

Type 1
Type IIx

IIa are moderately fatigable

Question 14

What is the Capillary to fiber ratio?

Answer 14

number of capillaries surrounding a muscle fiber

Question 15

What do capillaries do for muscle fiber? why capillaries and not arteries?

Answer 15

• supply muscle with oxygen and nutrients

- more diffusion can occur when blood remains for longer periods

Question 16

Transit time?

Answer 16

amount of time the blood remains in the capillary

Question 17

What happens when you increase capillary to fiber ratio?

Answer 17

• reduce velocity of blood flow
• increase transit time
• decrease distance nutrients and oxygen have to travel
• increases slow twitch fibers oxidative capacity

Question 18

Mitochondrial density? FT vs ST?

Answer 18

• fibers have many mitochondria
• more oxidative capacity
• slow twitch fibers have more than fast twitch

Question 19

What is Myoglobin?

Answer 19

• equivalent of hemoglobin in the blood, but in muscle fibers
• binds with oxygen in fibers and carries it to mitochondria

Question 20

Why are slow twitch fibers more red in color?

Answer 20

Myoglobin is red, slow twitch have a high content of it

Question 21

What is peak tension?

Answer 21

contractile force of a single twitch of an isolated fiber or motor unit

Question 22

The amount of force a fiber can produce during contraction is directly related to _____ of the fiber.

Answer 22

size (CSA)

Question 23

FT fibers are generally ______ than ST fibers. Result?

Answer 23

larger, they have more myofibrils in parallel and produce more force

Question 24

What is a better way to compare fibers other than peak tension? why?

Answer 24

peak specific tension b/c it is relative to fiber size

Question 25

Peak specific tension?

Answer 25

amount of force produced per unit of CSA (Po/CSA)

Question 26

When normalized with peak specific tension, why do FT fibers still produce more force?

Answer 26

more densely packed myofibrils

Question 27

What happens when the sarcomere is longer or shorter than normal?

Answer 27

- force of production is reduced - shortened- actin/myosin overlap too much - lengthened- fewer myosin heads can attach the actin

Question 28

What is the optimal length of a muscle fiber?

Answer 28

sarcomeres are 100-120% of normal resting length | -optimal overlap of actin and myosin, maximizing number of myosin heads that can attach

Question 29

What is shortening velocity?

Answer 29

speed at which a single unloaded fiber can shorten, it is directly related to activity of Myosin ATPase (Fiber Lengths per second, FL/s)

Question 30

Higher shortening velocities are expected in what fibers?

Answer 30

longer fibers that have more sarcomeres in series (IIx)

Question 31

Maximal shortening velocity (Vmax) occurs when ______.

Answer 31

muscle is unloaded

Question 32

At maximal loading, shortening velocity is _____.

Answer 32

zero (isometric)

Question 33

At any give peak tension, type I fibers contract _____ than type II and produce _____ force.

Answer 33

slower | less

Question 34

Time to peak tension?

Answer 34

faster shortening velocity = faster time to peak tension | Type IIx

Question 35

How is contractile power calculated?

Answer 35

Force * Velocity (IIx has most power, I has least)

Question 36

What is twitch duration?

Answer 36

sum of its contraction phase and relaxation phase

Question 37

What largely determines twitch duration?

Answer 37

- how fast the sarco reticulum can re-uptake calcium from sarcoplasm - faster=shorter twitch duration - FT= shorter duration