Week 12 lec - Skeletal muscle pathology Flashcards
what percentage of a healthy person’s body is muscle?
40%
Skeletal muscle consists of what 4 things?
- Muscle tissue
- Connective tissue
- Nerve and blood supply
- Satellite cells
what are the 3 connective tissue layers in skeletal muscle?
3 connective tissue layers:
- Epimysium – tough outer layer gives shape (large collagen bundles).
- Perimysium - surrounds bundles (fascicles) of myofibres (loose CT – BV).
- Endomysium - encloses individual myofibres (fine collagen fibres).
what is the diameter of a muscle fibre in an adult?
50μm
what causes the striated appearance in skeletal muscle?
A band, I band, Z line
what does a motor unit consist of?
a single motor neuron and all the myofibres it innervates (2-2000)
in humans, how many motor units does each muscle contain?
hundreds
in terms of skeletal muscle plasticity, what 3 changes can occur?
- Hypertrophy
- Atrophy
- Regeneration
what is the term used to describe a degenerative loss of skeletal muscle?
sarcopenia
what are satellite cells?
muscle specific stem cells (the precursor for a muscle cell)
what do satellite cells do?
Facilitate post-natal muscle growth and regeneration
where do satellite cells normally reside?
between the sarcolemma and basement membrane
in what state are satellite cells normally in?
quiescent state
what causes satellite cells to activate, proliferate, differentiate and fuse into myofibres?
injury or resistance exercise
how can you tell th difference between a satellite cell and muscle cell nucleus?
what does all postnatal muscle growth depend on?
the activation, proliferation and fusion of satellite cells with existing myofibres
what happens to the protein to DNA ratio of the myofibre during hypertrophy?
it stays the same due to fusion of satellite cells
how does skeletal muscle adapt to an increase in workload?
by increasing the size and amount of contractile proteins within the sarcomeres of each myofibre
what endogenous or exogenous hormones can trigger hypertrophy?
- Insulin-like growth factor-1 (IGF-1)
- growth hormone (GH)
- anabolic steroids.
what are the 4 steps of hypertrophy?
- Resistance exercise, physiological loading, testosterone or enhanced nutrition
- Activation, proliferation and subsequent fusion of satellite cells with existing myofibres
- Increase in the amount of contractile proteins within each myofibre. Protein synthesis > protein degradation. Increase mitochondrial content.
- Increase in the size and diameter (CSA) of individual myofibres. Increase in associated muscle strength (force production) Increase fatigue resistance
what are the benefits of using anabolic steroids?
- Increase muscle mass
- High levels of peak power and strength
- Increase RBC count, aid in recovery
- Increase determination and aggression
Male testosterone about 25x higher than females so females have a lot more to gain by using it
- Tendons susceptible to injury
- CVS, liver, kidney problems, CM fibrosis, BP
- Reduced LH and FSH concentrations = Reduced / inhibited gametogenesis = Male and female infertility – due to suppression of HPA axis
what biochemical and enzymatic responses are responsible for muscle atrophy?
the reduced capacity to synthesize new protein and the up-regulation of pathways leading to increased protein breakdown (e.g. ubiquitin pathway)
factors which cause atrophy?
- ageing (sarcopenia)
- disuse (immobilisation)
- denervation
- inflammatory conditions associated with cancer (cachexia), burns and anorexia/starvation
