Muscle structure and adaptation

Question 1

What do muscles form from?

Answer 1

Form from the somites

Question 2

What are somites?

Answer 2

Somites are blocks of bilateral paired paraxial mesoderm

Question 3

What happens during the development of skeletal muscle?

Answer 3

• Mesodermal cells go through an epithelial to mesenchymal transition where they become columnar and form a transient cavity
• Then the sclerotome forms which makes up the bone, ribs and cartilage
• In between the dermatome and sclerotome, the mytones form
• In between the myotone and the sclerotome, the syndetome forms, which are tendons

Question 4

Steps involved in myogenesis

Answer 4

1. Paracrine factors induce MyF5 and MyoD causing myogenic commitment(myoblasts)
2. Myoblasts proliferate under the control of growth factors
3. Cell cycle exit and there’s myogenin expression causing terminal differentiation
4. Structural proteins are expressed and myotubes form
5. Myotubes align and fuse

Question 5

In what way do muscles develop and why?

Answer 5

Muscle develop in a biphasic way as primary fibre form and secondary fibres form depending on the architecture of the primary fibres

Question 6

What are satellite cells involved in?

Answer 6

Satellite cells are involved in regeneration and hypertrophy of the muscles

Question 7

When is fibre number set and what determines it?

Answer 7

Fibre number is set at birth

-Genetically determined

Question 8

What can fibre number be affected by?

Answer 8

Can be affected by temperature, hormones, nutrition and innervation

Question 9

How is postnatal muscle growth:hypertrophy?

Answer 9

• After birth, increase in muscle mass due to increase in fibre size
• MuSC’s are activated and proliferate and are incorporated into muscle fibre

Question 10

What are muscle stem cells(MuSC’s) called and what are they?

Answer 10

MuSC’s are called satellite cells and are undifferentiated muscle precursors and are self renewing

Question 11

When do MuSC’s return to quiescence?

Answer 11

Return to quiescence when not needed

Question 12

Why are muscle fibres multinucleated and have a maintained cytoplasm:nuclei ratio?

Answer 12

Muscle fibres are multinucleated and have a maintained cytoplasm:nuclei ratio as its a very large cell

Question 13

What does molecular variability of muscle fibres depend on?

Answer 13

Depend on their function

Question 14

Why are there multiple isoforms of myofibrillar proteins?

Answer 14

Multiple isoforms due to alternate splicing or promoters

Question 15

What does a change in titin isoform result in?

Answer 15

Slight changes in titin isoforms change elastic properties

Question 16

What does a change in myosin isoform result in?

Answer 16

Changes in myosin isoform change the speed which it can fuse and bind to actin and the speed at which it can hydrolyse ATP

Question 17

What do changes to troponin and tropomyosin influence?

Answer 17

Changes to troponin and tropomyosin will influence the sensitivity of the muscle fibre to calcium

Question 18

What will changes in the isoform of the different fibre types have an overall effect of?

Answer 18

Will have an overall effect in resistance of that muscle fibre to fatigue

Question 19

What are type 1 fibres?

Answer 19

These are slow muscles

Question 20

Are type 1 fibres exhaustible?

Answer 20

No, virtually inexhaustible

Question 21

Adaptability of type 1 fibres

Answer 21

• Have a high mitochondrial content for aerobic respiration

- Have an extensive blood supply and abundant myoglobin

Question 22

What are type 2 fibres?

Answer 22

These are fast muscle

Question 23

What do type 2 fibres produce?

Answer 23

Produce high force contractions

Question 24

Fatigue in type 2 fibres

Answer 24

Fatigue easily

Question 25

Adaptations of type 2 fibres

Answer 25

- Few mitochondria as it undergoes glycolytic respiration | - Poorly vascularized and lack myoglobin

Question 26

What are a marathon runners adaptations to their environment?

Answer 26

1. Muscles small but fatigue resistant 2. Muscle dense and strong for their size 3. Work over very long periods of time

Question 27

What are a sprinters adaptations to their environment?

Answer 27

1. Rapid powerful contractions 2. Easily fatigued at maximum effect 3. High force per cross sectional area of muscle

Question 28

What are a powerlifters adaptations to their environment?

Answer 28

1. Muscles are hypertrophied 2. Highly glycolytic 3. Fatigue easily 4. High muscle to total body mass ratio 5. Muscle size interfere with locomotion

Question 29

What is a testerone?

Answer 29

A natural anabolic androgenic steroid

Question 30

What does testosterone promote the commitment of?

Answer 30

Promotes the commitment of mesenchymal pluripotent cells into myogenic lineage and inhibit adipogenesis

Question 31

What does testosterone stimulate?

Answer 31

Stimulates: - Satellite cells replication - Muscle protein synthesis - Fibre hypertrophy

Question 32

What is sarcopenia?

Answer 32

It is age related loss of muscle mass

Question 33

What is loss of muscle mass associated with?

Answer 33

Loss of muscle mass associated with gain in fat mass

Question 34

What is muscle ageing associated with?

Answer 34

Associated with decreased satellite cell number and recruitment

Question 35

What are the biochemical and metabolic changes that come around due to muscle ageing?

Answer 35

- Mitochondrial mutations | - Reduced oxidative and glycolytic enzyme activity