Unit 10 - Skeletal Muscle Growth, Development and Organization Flashcards
What is the carcass composed of?
- bones
- connective tissue (collagen)
- lean tissue (muscle tissue)
- adipose tissue (subcutaneous, intermuscular, intramuscular)
What carcass traits are we looking for?
- maximum muscle tissue
- fair amount of fat tissue
- a lowest proportion of bone as possible
What is the carcass yield?
how much of carcass we actually use for meat
What is the goal of getting the best carcass traits?
determine the best slaughter time for the most lean tissue and fair amount of fat
when does muscle and fat deposition increase?
during puberty
What happens to carcass at the finishing phase?
fat deposition rate is higher than muscle, different production strategies must be used to enhance muscle mass without compromise fat deposition
What is myogenesis?
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
What are the steps to myogenesis?
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
how are myogenic precursor cells created
cells can be anything, but embryonic environment differentiates them into myogenic precursor cells
Are the number of muscle fibers set at birth?
yes
muscle just increases in size and volume, some myoblasts wont fuse together and will be used to repair fibers and proliferate more
why do men have more muscle mass than women?
testosterone tells myoblasts (which have a testosterone receptor) to increase muscle fiber size, this is why males have more lean muscle,
Why do we have hormone implants in castrates?
the hormones mimic the testosterones function on the myoblasts to grow muscle mass
How many populations do muscle fibers develop from?
two
What are the two distinct populations that muscle fibers develop from during myogenesis?
- 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
What are satellite cells?
another population of myoblasts that does not form fibres but stays close to the myofibres
What is the function of satellite cells?
- 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
When does myogenesis take place?
takes place prenatally and the number of muscle fibres is set at birth
How does muscle growth postnatally occur if muscle fibers remain the same?
during postnatal growth, the increase in skeletal muscle mass is mainly due to an increase in muscle fibre size (hypertrophy)
What is hypertrophy?
increase in muscle fibre size
What does postnatal muscle fibre hypotrophy depend on?
the total number of muscle fibres within a muscle
What does increased muscle hypertrophy look like on the microscope?
small hypertrophy, more muscle fibres seen
more muscle hypertrophy has less cells seen and larger muscle fibres
What does lean growth depend on?
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
What can protein restriction during mid gestation cause?
less muscle fibers and therefore less hypertrophy
What are the three layers of muscle connective tissue?
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
What is the tissue like on muscles used for power?
muscles used for power contains a thicker connective tissue layer compared to muscles used for coordination
Why is it better for meat quality to slaughter younger animals?
older the animal gets, more cross linking between collagen molecules which causes toughness
What are some features of muscle fibers?
- basic unit of muscle
- long cylindrical tubular cells
How many fibers are there per bundle?
can range from 50-300
What is fiber diameter affected by?
- difference between species and muscles
- exercise, animal maturity, and diet
- animal genetics
what are t-tubules?
invaginations of the sarcolemma (membrane of the striated muscle)
What are t tubules associated with?
sarcoplasmic reticulum
What does the sarcoplasmic reticulum store?
Ca2+
What do t tubules and sarcoplasmic work together to do?
to release calcium throughout the length of the muscle fiber
What is a myofibril?
subcellular structures specialized in contractile activity
How much of total protein do myofibrils make up?
50% and are not encased in membrane
what is a sarcomere?
subunit of a myofibril, basic contractile unit of a muscle fiber, myofibril is a series of several hundred to thousands of sarcomeres
Why is aged meat more tender than non-aged meat?
enzymes chew proteins (sarcomere filaments) which allows for less structure in the meat at 4C enzymes eat at z line
What is the structure of the sarcomere?
Z-line and then M line and then I band ( from one z line to the next)
what is the sarcomeres length in a relaxed muscle?
2.8-2.8 microm
What is the sarcomeres length in a contracted muscle
2 microm or less
What are the two filaments within the sarcomere?
thin and thick filaments
What are the three proteins within the thin filament?
troponin
actin
tropomyosin
What are the thick filaments made up of?
myosin, heads and tails
What do myosin heads contain?
actin binding sites and ATP binding sites
How do myosin and actin interact in order to contract the muscle?
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
What does tropomyosin do?
- protein on the thin filament
- blocks myosin binding at the relaxed stage
What does troponin do?
- protein on thin filament
- binds actin
- binds tropomyosin
- binds calcium
What does actin do?
- protein on the thin filament
- formed by subunits with sites to bind myosin
