Unit 10 - Skeletal Muscle Growth, Development and Organization

Question 1

What is the carcass composed of?

Answer 1

• bones
• connective tissue (collagen)
• lean tissue (muscle tissue)
• adipose tissue (subcutaneous, intermuscular, intramuscular)

Question 2

What carcass traits are we looking for?

Answer 2

• maximum muscle tissue
• fair amount of fat tissue
• a lowest proportion of bone as possible

Question 3

What is the carcass yield?

Answer 3

how much of carcass we actually use for meat

Question 4

What is the goal of getting the best carcass traits?

Answer 4

determine the best slaughter time for the most lean tissue and fair amount of fat

Question 5

when does muscle and fat deposition increase?

Answer 5

during puberty

Question 6

What happens to carcass at the finishing phase?

Answer 6

fat deposition rate is higher than muscle, different production strategies must be used to enhance muscle mass without compromise fat deposition

Question 7

What is myogenesis?

Answer 7

a process of skeletal muscle formation (hyperplasia)
during embryonic developent, myoblasts develop from myogenic precursor cells which are of medodermal origin
these cells are determined to enter the myogenic linear and are able to proliferate and divide to establish a pool of myoblasts

Question 8

What are the steps to myogenesis?

Answer 8

myogenic precursor cells -> (determination) determined myoblasts which are muscle cells (proliferation) -> (differentiation) fuse together into differentiated myotubes -> (modulation) maturation and reorganization makes the muscle fiber

Question 9

how are myogenic precursor cells created

Answer 9

cells can be anything, but embryonic environment differentiates them into myogenic precursor cells

Question 10

Are the number of muscle fibers set at birth?

Answer 10

yes
muscle just increases in size and volume, some myoblasts wont fuse together and will be used to repair fibers and proliferate more

Question 11

why do men have more muscle mass than women?

Answer 11

testosterone tells myoblasts (which have a testosterone receptor) to increase muscle fiber size, this is why males have more lean muscle,

Question 12

Why do we have hormone implants in castrates?

Answer 12

the hormones mimic the testosterones function on the myoblasts to grow muscle mass

Question 13

How many populations do muscle fibers develop from?

Answer 13

two

Question 14

What are the two distinct populations that muscle fibers develop from during myogenesis?

Answer 14

• fibres which form during the initial stages of myoblast fusion are primary myofibers
• secondary fibers these are formed from foetal myoblasts during a second wave of differentiation

Question 15

What are satellite cells?

Answer 15

another population of myoblasts that does not form fibres but stays close to the myofibres

Question 16

What is the function of satellite cells?

Answer 16

• they are able to divide and they serve as the source of new myonuclei during postnatal growth
• contribute to growth of the fibres and also participate in the regeneration process

Question 17

When does myogenesis take place?

Answer 17

takes place prenatally and the number of muscle fibres is set at birth

Question 18

How does muscle growth postnatally occur if muscle fibers remain the same?

Answer 18

during postnatal growth, the increase in skeletal muscle mass is mainly due to an increase in muscle fibre size (hypertrophy)

Question 19

What is hypertrophy?

Answer 19

increase in muscle fibre size

Question 20

What does postnatal muscle fibre hypotrophy depend on?

Answer 20

the total number of muscle fibres within a muscle

Question 21

What does increased muscle hypertrophy look like on the microscope?

Answer 21

small hypertrophy, more muscle fibres seen
more muscle hypertrophy has less cells seen and larger muscle fibres

Question 22

What does lean growth depend on?

Answer 22

the number of the prenatally formed fibres and on the degree of their postnatal hypertrophy
- how the in-utero development occurs ill impact the muscle growth postnatally and thus, the lean tissue deposition

Question 23

What can protein restriction during mid gestation cause?

Answer 23

less muscle fibers and therefore less hypertrophy

Question 24

What are the three layers of muscle connective tissue?

Answer 24

epimysium: layer of connective tissue surrounding the skeletal muscle
perimysium: layer of connective tissue surrounding the muscle bundles
endomysium: layer of connective tissue surrounding the muscle fibers

Question 25

What is the tissue like on muscles used for power?

Answer 25

muscles used for power contains a thicker connective tissue layer compared to muscles used for coordination

Question 26

Why is it better for meat quality to slaughter younger animals?

Answer 26

older the animal gets, more cross linking between collagen molecules which causes toughness

Question 27

What are some features of muscle fibers?

Answer 27

• basic unit of muscle
• long cylindrical tubular cells

Question 28

How many fibers are there per bundle?

Answer 28

can range from 50-300

Question 29

What is fiber diameter affected by?

Answer 29

• difference between species and muscles
• exercise, animal maturity, and diet
• animal genetics

Question 30

what are t-tubules?

Answer 30

invaginations of the sarcolemma (membrane of the striated muscle)

Question 31

What are t tubules associated with?

Answer 31

sarcoplasmic reticulum

Question 32

What does the sarcoplasmic reticulum store?

Answer 32

Ca2+

Question 33

What do t tubules and sarcoplasmic work together to do?

Answer 33

to release calcium throughout the length of the muscle fiber

Question 34

What is a myofibril?

Answer 34

subcellular structures specialized in contractile activity

Question 35

How much of total protein do myofibrils make up?

Answer 35

50% and are not encased in membrane

Question 36

what is a sarcomere?

Answer 36

subunit of a myofibril, basic contractile unit of a muscle fiber, myofibril is a series of several hundred to thousands of sarcomeres

Question 37

Why is aged meat more tender than non-aged meat?

Answer 37

enzymes chew proteins (sarcomere filaments) which allows for less structure in the meat at 4C enzymes eat at z line

Question 38

What is the structure of the sarcomere?

Answer 38

Z-line and then M line and then I band ( from one z line to the next)

Question 39

what is the sarcomeres length in a relaxed muscle?

Answer 39

2.8-2.8 microm

Question 40

What is the sarcomeres length in a contracted muscle

Answer 40

2 microm or less

Question 41

What are the two filaments within the sarcomere?

Answer 41

thin and thick filaments

Question 42

What are the three proteins within the thin filament?

Answer 42

troponin
actin
tropomyosin

Question 43

What are the thick filaments made up of?

Answer 43

myosin, heads and tails

Question 44

What do myosin heads contain?

Answer 44

actin binding sites and ATP binding sites

Question 45

How do myosin and actin interact in order to contract the muscle?

Answer 45

myosin heads on thick filament have actin binding sites, calcium is released inside the muscle, the calcium binding sites on the troponin proteins in the thin filaments makes it heavier and moves away troponin itself and tropomyosin which was covering the myosin binding sites on the actin molecules on the thin filaments. This allows the myosin head to connect with the actin on the thin filaments. ATP is needed to break the connection between myosin and actin, ATP binds to the ATP binding sites on the myosin heads

Question 46

What does tropomyosin do?

Answer 46

• protein on the thin filament
• blocks myosin binding at the relaxed stage

Question 47

What does troponin do?

Answer 47

• protein on thin filament
• binds actin
• binds tropomyosin
• binds calcium

Question 48

What does actin do?

Answer 48

• protein on the thin filament
• formed by subunits with sites to bind myosin