Muscle structure and adaptation Flashcards
What do muscles form from?
Form from the somites
What are somites?
Somites are blocks of bilateral paired paraxial mesoderm
What happens during the development of skeletal muscle?
- 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
Steps involved in myogenesis
- Paracrine factors induce MyF5 and MyoD causing myogenic commitment(myoblasts)
- Myoblasts proliferate under the control of growth factors
- Cell cycle exit and there’s myogenin expression causing terminal differentiation
- Structural proteins are expressed and myotubes form
- Myotubes align and fuse
In what way do muscles develop and why?
Muscle develop in a biphasic way as primary fibre form and secondary fibres form depending on the architecture of the primary fibres
What are satellite cells involved in?
Satellite cells are involved in regeneration and hypertrophy of the muscles
When is fibre number set and what determines it?
Fibre number is set at birth
-Genetically determined
What can fibre number be affected by?
Can be affected by temperature, hormones, nutrition and innervation
How is postnatal muscle growth:hypertrophy?
- After birth, increase in muscle mass due to increase in fibre size
- MuSC’s are activated and proliferate and are incorporated into muscle fibre
What are muscle stem cells(MuSC’s) called and what are they?
MuSC’s are called satellite cells and are undifferentiated muscle precursors and are self renewing
When do MuSC’s return to quiescence?
Return to quiescence when not needed
Why are muscle fibres multinucleated and have a maintained cytoplasm:nuclei ratio?
Muscle fibres are multinucleated and have a maintained cytoplasm:nuclei ratio as its a very large cell
What does molecular variability of muscle fibres depend on?
Depend on their function
Why are there multiple isoforms of myofibrillar proteins?
Multiple isoforms due to alternate splicing or promoters
What does a change in titin isoform result in?
Slight changes in titin isoforms change elastic properties
What does a change in myosin isoform result in?
Changes in myosin isoform change the speed which it can fuse and bind to actin and the speed at which it can hydrolyse ATP
What do changes to troponin and tropomyosin influence?
Changes to troponin and tropomyosin will influence the sensitivity of the muscle fibre to calcium
What will changes in the isoform of the different fibre types have an overall effect of?
Will have an overall effect in resistance of that muscle fibre to fatigue
What are type 1 fibres?
These are slow muscles
Are type 1 fibres exhaustible?
No, virtually inexhaustible
Adaptability of type 1 fibres
- Have a high mitochondrial content for aerobic respiration
- Have an extensive blood supply and abundant myoglobin
What are type 2 fibres?
These are fast muscle
What do type 2 fibres produce?
Produce high force contractions
Fatigue in type 2 fibres
Fatigue easily
Adaptations of type 2 fibres
- Few mitochondria as it undergoes glycolytic respiration
- Poorly vascularized and lack myoglobin
What are a marathon runners adaptations to their environment?
- Muscles small but fatigue resistant
- Muscle dense and strong for their size
- Work over very long periods of time
What are a sprinters adaptations to their environment?
- Rapid powerful contractions
- Easily fatigued at maximum effect
- High force per cross sectional area of muscle
What are a powerlifters adaptations to their environment?
- Muscles are hypertrophied
- Highly glycolytic
- Fatigue easily
- High muscle to total body mass ratio
- Muscle size interfere with locomotion
What is a testerone?
A natural anabolic androgenic steroid
What does testosterone promote the commitment of?
Promotes the commitment of mesenchymal pluripotent cells into myogenic lineage and inhibit adipogenesis
What does testosterone stimulate?
Stimulates:
- Satellite cells replication
- Muscle protein synthesis
- Fibre hypertrophy
What is sarcopenia?
It is age related loss of muscle mass
What is loss of muscle mass associated with?
Loss of muscle mass associated with gain in fat mass
What is muscle ageing associated with?
Associated with decreased satellite cell number and recruitment
What are the biochemical and metabolic changes that come around due to muscle ageing?
- Mitochondrial mutations
- Reduced oxidative and glycolytic enzyme activity
