Muscle Structure And Adaptation

Question 1

What do muscles form from in the embryo?

Answer 1

→ Somites (paraxial mesoderm)

Question 2

What happens to mesodermal cells during development?

Answer 2

→ They go through a mesenchymal transition
→ The cells become columnar and form a transient cavity
→ They undergo an epithelial mesenchymal transition to form the sclerotome

Question 3

What does the sclerotome consist of?

Answer 3

→ Bone
→ Ribs
→ Cartilage

Question 4

What is the myotome?

Answer 4

→ Muscle precursors

Question 5

What is the dermomyotome?

Answer 5

→ Myotome and dorsal dermis

Question 6

What is the syndetome?

Answer 6

→ Tendons

Question 7

What does the notochord do?

Answer 7

→ Induces the mesoderm to become myogenic by inducing myogenic regulatory factors

Question 8

What do paracrine factors induce?

Answer 8

→ Myf5 and MyoD (myogenic transcription factors)

Question 9

Describe myogenesis

Answer 9

→ Notochord induces mesoderm to become myogenic
→ Paracrine factors induce Myf5 and MyoD which leads to myogenic commitment
→ myoblasts proliferate
→ Exit the cell cycle due to myogenin expression
→Structural proteins are expressed and myotubes form
→ Myotubes align and fuse parallel to each other
→ Biphasic muscle development : primary and secondary
→ Satellite cells : regeneration and post natal growth

Question 10

What does myogenin expression mean?

Answer 10

→terminal differentiation

Question 11

What are the structural proteins expressed when myotubes form?

Answer 11

→ Actin and myosin

Question 12

What can embryonic fibre number be affected by?

Answer 12

→ temperature
→ hormones
→ Nutrition
→ Innervation

Question 13

What happens to muscle mass after birth?

Answer 13

→ Increase in fibre size (hypertrophy)

Question 14

What are satellite cells?

Answer 14

→ Muscle stem cells

Question 15

What are muscle stem cells?

Answer 15

→ Undifferentiated muscle precursors that are self-renewing

Question 16

When are MuSCs activated?

Answer 16

→ training

→ postnatal development

Question 17

Why are muscle cells multinucleated?

Answer 17

→ They are big and long cells
→ huge production of structural proteins
→ this needs to occur along the length of the muscle fibre

Question 18

What do myosin isoforms dictate?

Answer 18

→ Different chemomechanical transduction
→ ATP hydrolysis
→ Shortening velocity

Question 19

What do troponin and tropomyosin isoforms dictate?

Answer 19

→ Determine sensitivity to Ca2+

Question 20

What do titin isoforms dictate?

Answer 20

→ Elastic properties

Question 21

What is an example of a type I fibre?

Answer 21

→ Back extensor muscle

Question 22

What are type I fibres used for?

Answer 22

→ Posture

Question 23

What are the properties of type I fibres?

Answer 23

→ High mitochondrial content - oxidative phosphorylation
→ Heavily vascularised
→ Sustained contraction
→ Abundant myoglobin

Question 24

What are the properties of type II fibres?

Answer 24

→ High force contraction
→Fatigue easily
→ Less mitochondria - glycolytic respiration
→ Poorly vascularised

Question 25

What ratio of muscle fibres do untrained individuals have?

Answer 25

→ 50:50 fast to slow

Question 26

What ratio of muscle fibres do long distance runners have?

Answer 26

→ 60-70% slow

Question 27

What ratio of muscle fibres do sprinters have?

Answer 27

→ 80% fast

Question 28

What are properties of powerlifters muscles?

Answer 28

``` → Hypertrophied → Highly glycolytic → Fatigue easily → High muscle to total body mass ratio → muscle size interferes with locomotion ```

Question 29

What is the order that MHC can split ATP in from fastest to slowest?

Answer 29

``` → 2B → 2A → 2X → 1 → embryonic is the slowest ```

Question 30

What is MHCexoc?

Answer 30

→ extraocular myosin heavy chain

Question 31

What is MHCperi?

Answer 31

→ perinatal myosin heavy chain

Question 32

What are the gene differences between males and females in terms of skeletal muscles?

Answer 32

→ >3000 genes | → males have a larger fibre cross-sectional area

Question 33

What is the difference between females and males in type I fibres?

Answer 33

→ males - 36% | → females - 44%

Question 34

What is the difference between females and males in type II fibres?

Answer 34

→ males - 41% | → females - 34%

Question 35

What is testosterone needed for?

Answer 35

→ development of the male reproductive system

Question 36

What does testosterone develop?

Answer 36

→ Muscle + bone mass → body hair → deep voice

Question 37

What kind of a steroid is testosterone?

Answer 37

→ Anabolic

Question 38

What does testosterone do to muscle cells?

Answer 38

→ Commitment of mesenchymal pluripotent cells into myogenic lineage

Question 39

What does testosterone inhibit?

Answer 39

→ inhibits adipogenesis

Question 40

What does testosterone stimulate?

Answer 40

→ Satellite cell replication → muscle protein synthesis → fibre hypertrophy

Question 41

What are the three adverse effects that synthetic anabolic steroids can have?

Answer 41

→ Increase BP → affect the heart → Shrinkage of testicles

Question 42

What can be used for muscle mass loss?

Answer 42

→ testosterone

Question 43

How does muscle recover from a minor injury such as a sprain?

Answer 43

→ Damaged muscle fibres necrose → There is an inflammatory response and neutrophils and macrophages respond to the damaged muscle fibre → There is an increase in satellite cell proliferation → they fuse with muscle fibres and regenerate them

Question 44

How does muscle recover from laceration?

Answer 44

→ incomplete laceration | → fibrotic tissue forms

Question 45

What is sarcopenia?

Answer 45

→ age related loss of muscle mass

Question 46

How much does muscle mass decrease after 30?

Answer 46

→ 3-8% decrease after 30 | → higher after 60

Question 47

What is loss of muscle mass associated with?

Answer 47

→ gain in fat mass | → decreased satellite cell number and recruitment