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NUFS 374 > Muscle structure & composition > Flashcards

Muscle structure & composition Flashcards

1
Q

What are the 3 muscle types in the animal body? what type of control do they have?

A

Skeletal - voluntary
Smooth - involuntary
Cardiac - involuntary

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2
Q

What is the implication of skeletal muscle’s structure?

A

Key in meat science, striated and multi-nucleated with nuclei at the periphery

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3
Q

What is the sequence of muscle fiber development during prenatal myogenesis?

A

Stem cells → myoblasts → myotubes → myofibers

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4
Q

What happens to satellite cells (stem cells) postnatally?

A

Activated by stress or injury, they divide asymmetrically
-can produce new myofibers or add nuclei to existing fibers

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5
Q

how do primary and secondary myofibers differ?

A

primary myofibers are larger in structure for organization, alignments and fusion into secondary fibers

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6
Q

Why are muscle fibers multinucleated?

A
  • Fusion of many mononucleated myoblasts
  • Long cells require multiple nuclei
  • High energy demand necessitates multiple mitochondria
  • High protein synthesis requires distributed nuclei
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7
Q

What is the hierarchy of muscle structure?

A
  • Muscle → Muscle fiber bundle (fascicle) → fiber → myofibril → myofilament
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8
Q

what 3 kinds of tissue does a muscle have? what are they responsible for?

A

1) muscle tissue
-muscle fibers/myofibers
2) adipose tissue
-marbling
3) connective tissue (epimysium, perimysium, endomysium)
-protection + contraction of muscle fibers

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9
Q

What are the layers of the muscle? what do they do?

A

epimysium: surrounds entire muscle
perimysium: surrounds buncles of fiber
endomysium: surrounds individual muscle fibers

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10
Q

what strutcure of the muscle cell contains muscle fibers? what is contained inside of this?

A

muscle fascicles contain muscle fibers
-myofibrils are contained inside muscle fibers

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11
Q

What is the contractile unit of muscle? where is this located? how do each of the bands change during contraction?

A

Sarcomere
-located inside myofibrils

A-band: Myosin length (unchanged during contraction)

I-band & H-zone: Shrink during contraction

M-line, Z-line, titin: structural anchors.

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12
Q

what filaments are sarcomeres made of?

A

actin (thin) and myosin (thick) filaments

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13
Q

what proteins are in actin?

A

nebulin, troponin, tropomyosin, tropomodulin

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14
Q

where is the sarcoplasmic retiiculum located? what is its function?

A

it surrounds myofibrils and acts to sequester ca2+ through Ca ATPase pump

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15
Q

What is the function of T-tubules? where are they located?

A

they are extensions of the sarcolemma and they regulate action potentials by opening Ryr gate to release Ca2+

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16
Q

What triggers muscle contraction at the molecular level?

A

Ca²⁺ binds troponin C (TnC) → tropomyosin moves → myosin binds

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17
Q

What are the three solubility categories of muscle proteins? provide examples of each protein.

A

1) Myofibrillar (Salt-soluble)
-contractile (actin/myosin), regulatory (troponin/tropomyosin), structural (titin,nebulin,desmin)

2) Sarcoplasmic (Water-soluble)
-enzymes, myoglobin, cytochromes

3) Connective tissue/ stromal (Acid/alkaline soluble)
-collagen, elastin, proteoglycans

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18
Q

what is myosin? what is the function?

A

thick filament muscle protein responsible for hydrolyzing ATP -> releasing ADP + Pi + energy
- needed to contract muscles

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19
Q

what is the thin filament? what is its function? what is it composed of?

A

Thin muscle protein filament that is comprised of:
1) actin: globular regulatory ptotein
2) tropomyosin: rod like molecule forming helix
3) Troponin: protein containing Troponin C (binds Ca), Troponin I (inhibits tropomyosin), Troponin T (attaches tropomysin)

Forms the track for myosin heads to “walk” on during contraction

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20
Q

What is collagen? What is the structure of collagen?

A

The main connective tissue in meat
-Composed of repeating units of proline and hydroxyproline

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21
Q

What effect does increased collagen have on meat?

A

Tougher meat

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22
Q

What is the impact of cross-linking in collagen maturation?

A

Increases toughness, especially in older animals
-collagen has no strength if its not cross linked
-trivalent cross links =mature
-divalent cross links = immature

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23
Q

Why is young animal meat more tender?

A

Due to less cross-linking

Less cross-linking in collagen contributes to the tenderness of meat.

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24
Q

what part of an animal do you expect to be the most tender? and least?

A

more collagen = tougher meat
-legs, chest, rump have higher amounts of collagen (less tender)
-rib, loin and sirloin have less collagen = more tender

Enzymatic processes break down proteins, making meat more tender over time.

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25
What are action potentials? How are they generated? where does this occur?
Electrical impulses that propagate along the muscle fiber's membrane 1) local depolarization 2) generation + propogation of AP -occurs along sarcolemma and T-tubules 3) Repolarization
26
What happens at the neuromuscular junction?
Action potential triggers release of ACh from movement of Ca2+, which binds to receptors on the sarcolemma Binding of ACh regulates movement of Na+/K+ ACh effects terminated by acetylcholinesterase
27
What is excitation-contraction coupling? what overall steps are involved?
The process linking the neural signal and muscle contraction through Ca²⁺ release in the sarcolemma 1) AP propogation down T-tubules -interaction with voltage-sensitive DHPR senses propogation and activates ryanodine receptor 2) Ca2+ release through ryanodine receptor 3) Ca binding to troponin C removing tropomyosin 4) myosin binds to actin forming cross bridge 5) power stroke / muscle contraction
28
What role does Ca²⁺ play in muscle contraction?
Ca²⁺ binds to troponin C, causing tropomyosin to shift and expose binding sites on actin
29
What is the power stroke? How does this relate to rigor mortis?
The pivoting of myosin heads that pulls actin filaments inward ATP needed to detach myosin head from actin, without it RIGOR MORTIS (muscle stiffening) occurs in post mortem muscle
30
How does muscle relaxation of skeletal muscle occur?
Reduction of ACh release causes repolarization, closing Ca2+ gates (less Ca2+ release) -Ca2+ pumped back into SR through ATP pumps
31
List the three major muscle fiber types and how they differ.
* Type I (Slow Oxidative) -tender, slower cooked red meats (thin fibre) * Type IIA (Fast Oxidative/Glycolytic) -pink/red meats * Type IIB (Fast Glycolytic) -less tender, more connective tissue
32
From when an animal dies to meat consumption, what are the steps involved?
1) removal of blood + O2 2) Complete deplation of ATP and creatine phosphate 3) Anaerobic glycolysis + lactate accumulation 4) Protein denaturation due to pH drop 5) structural modifications 6) enzymatic proteolysis on myofibril + connective tissues
33
When is muscle considered meat? what is this?
when 'rigor' has been resolved rigor = stiffening + loss of extensibility and it occurs when ATP is gone
34
What are the stages of rigor mortis?
* Delay: ATP present, muscle flexible * Onset: ATP low, cross-bridges form but can’t detach * Completion: ATP gone, full stiffness
35
what occurs during the delay phase of rigor mortis? what timefram does this typically occur?
ATP is either still available or generated through: 1) anaerobic glycolysis 2) Creatine phosphate The muscle is still extensible and rigor is delayed due to production of ATP (better for animal) -less than an hour (0-55min)
36
what occurs during the onset of rigor mortis? what timeframe does this typically occur?
Creatine phosphate is exhausted and anaerobic glycolysis becomes the main source energy -cross bridges form but dont detach due to ATP depletion -muscle begins to stiffen (1-3hr)
37
What occurs during the rigor completion phase? what timeframe does this typically occur?
all energy in the muscle is depleted and no regeneration occurs (complete stiffness) -3+ hours
38
what physical-chemical changes occur post mortem? what does this due to the meat? when does this occur?
decreases in pH impacts: 1) light scattering 2) WHC 3) protein denaturation
39
what is light scattering? why does it occur?
pH drops -> protein denaturation -> spaces form between structures and more light is scattered This leads to a pale appearance in the meat
40
How does pH affect WHC?
pH lowers closer to isoelectric point, which (around 5.0) reduces water retention due to protein denaturation -loss of water retention during processing and application of external forces
41
How does tenderness of meat increase when storage time is increased?
myofibrillar and cytoskeletal denaturation from proteolytic enzymes
42
what are the 4 major proteolytic enzymes involved in post mortem tenderization?
1) calpains * -Ca2+ dependent proteases which break down myofibrillar proteins (loosen structure without destroying) 2) lysosomal system 3) Ubiquitin-dependent proteasome 4) matric metalloproteinases
43
What is the role of cathepsin in postmortem aging?
lysosomal protease that works in the later stages of aging -breaks connective tissue to contribute to tenderization
44
What are matrix metalloproteinases (MMPs)?
Ca/Zn dependet enzymes that remodel collagen and connective tissue, aiding in meat tenderness -work in later stages of aging
45
what major factor has made poultry/pigs more susceptible to ante-mortem stressors?
genetic selection for rapid growth + increased muscle mass
46
What are the effects of stress on meat quality?
Increases risk of PSE and DFD meat, impacts animal welfare and final meat quality
47
What does PSE stand for and what are its characteristics?
Pale, Soft, Exudative ## Footnote Caused by short-term stress leading to rapid pH decline.
48
What does DFD stand for and what are its characteristics?
Dark, Firm, Dry ## Footnote Caused by long-term stress resulting in low glycogen and high pH.
49
What triggers the biochemical process leading to pH decline in meat?
Stress → adrenaline → cAMP cascade → glycogen breakdown
50
What is the ideal pH decline for meat quality?
Approximately 5.5 ## Footnote Crucial for meat texture and water holding capacity (WHC).
51
What mutation is associated with PSE meat?
RyR mutation (RYR1 gene)
52
How does a RyR mutation contribute to PSE?
Ca²⁺ leaks stimulate glycolysis, leading to a fast pH drop
53
What is a major consequence of PSE on meat texture?
Soft, exudative texture with decreased WHC
54
How can PSE be prevented?
Rapid chilling, gentle handling, genetic screening
55
What is the cause of DFD meat?
High pH (>6.0) due to less lactic acid from depleted glycogen
56
What are the characteristics of DFD meat?
Dark, firm, dry, high WHC due to charge repulsion
57
What is the downside of DFD meat?
Poor shelf life and increased microbial risk
58
What is cold shortening?
Pre-rigor meat chilled <10°C leading to uncontrolled contraction
59
What is thaw rigor?
Freezing before rigor causing calcium flooding and contraction on thaw
60
How can cold shortening and thaw rigor be prevented?
Electrical stimulation, delay chilling or freezing
61
What pigment is key to fresh meat color?
Myoglobin
62
What are the iron states in myoglobin and their colors?
Fe²⁺ (bright red, oxymyoglobin), Fe³⁺ (brown, metmyoglobin)
63
What effect does pH have on meat color stability?
Affects pigment stability and light reflection
64
What is the relationship between pH, WHC, and meat color?
↓ pH → ↑ protein denaturation → ↑ light scattering ↑ pH (DFD) → darker color, ↑ WHC
65
What factors affect meat texture?
Age, breed, gender, muscle function
66
What role does marbling play in meat quality?
Enhances tenderness, juiciness, and flavor
67
What are flavor precursors in meat?
Amino acids, sugars, fats, nucleotides
68
What reactions are key to cooked meat flavor?
Maillard reactions + lipid oxidation
69
What causes boar taint?
Androstenone & skatole in uncastrated males
70
How can boar taint be minimized?
Vaccination (Improvest®)
71
What are common poultry myopathies?
White striping, woody breast, spaghetti meat
72
What causes deep pectoral myopathy?
Ischemic necrosis due to muscle compression
73
What are key exam focus areas from this lecture?
Causes, mechanisms, and outcomes of PSE and DFD meat
74
Fill in the blank: Proper _______ decline is crucial for meat texture.
pH
75
True or False: High pH in meat is associated with PSE.
False
76
What is the effect of age on meat tenderness?
Older animals typically have tougher meat

NUFS 374 (5 decks)

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