Muscle Flashcards
What are the 3 muscle types?
- smooth
- striated
- cardiac
Describe the structure of skeletal muscle:
Striated
Syncytium (multiple nuclei)
Peripheral nuclei
Arranged into bundles known as fascicles
Very large and long
What are the 3 layers of connective tissue found in muscle?
Epimysium
- surrounds entire muscle
Perimysium
- surrounds bundles of muscle fibres
Endomysium
- surrounds individual muscle fibres
Why is connective tissue important?
Has a functional role, transferring information from the muscle to the tendons and a protective function as slightly stronger than muscle so can protect it from damage and tearing
What is a microfibril?
1 muscle fibre
What allows muscle to contract?
Actin and myosin
What are the 4 bands of sarcomere?
I band
- actin filaments alone
A band
- zones containing myosin
Z line
- defines boundary between sarcomeres
M-line
- transverse line in the middle of the sarcomere that binds the myosin filaments
What is the sliding filament theory?
Muscle shortening occurs due to movement of the actin filament over the myosin filament. This forms cross-bridges between the actin and myosin. It also reduces the distance between the Z-lines of the sarcomere.
What is tropomyosin?
Located along the 2 chains of actin filaments and has interactions with calcium that allow or prevent cross-bridge formation.
What is troponin?
Complex attached to each tropomyosin
Organise the layers of the muscle micro skeleton from lagers to smallest:
Myofilaments
Sacrolemma
Microfibrils
Sacrolemma
- muscle cell membrane
Myofibrils
- tube structures that pack the fibres
Myofilaments
- actin and myosin
As actin slides over myosin what is constantly happening?
Cross-bridges forming, releasing and reforming between the actin and myosin
What is the relationship between Ca2+ and Troponin?
Troponin captures Ca2+ and undergoes a conformational change that lifts tropomyosin away from the actin filament revealing the binding site for myosin driving cross-bridge formation.
What happens if calcium in low in supply
When calcium is low it blocks the binding of myosin to the actin fibre at rest
Does all muscle eventually fatigue?
No
Cardiac muscle doesn’t fatigue
Skeletal muscle can be fatigue resistant or will fatigue very quickly
What are the two types of individual muscle fibres?
Fast Fibres:
- Type IIa (fast oxidative)
- Type IIb (fast glycolitic)
- Type IIx (intermediate properties)
Slow Fibres:
- Type I fibres (slow oxidative)
How is fibre type composition analysed?
Immunochemistry
- each fibre has own specific myosin isoform
- looking at ATPase activity (more = faster muscle contraction)
- they each have specific metabolic profiles
Histochemical staining of fibre type
Identify the fibres:
(muscle group highlighted in red)
Can the muscle types found in different species be animal specific?
It depends on where the animal lives, what the animals main job is, genetics etc.
Example: Highlander Mice have significantly more slow oxidative fibres (type 1) than lowlander mice due to the altitude
Example: (see photo)
What is muscle fatigue?
What causes muscle fatigue?
Decreased maximum contractile force, its a protective mechanism so that muscles aren’t overworked
- ATP is required for the formation of cross bridges, muscles use up this ATP as they work
- as muscles work they produce inorganic phosphates, too much of this can affect the formation of this cross-bridges
- calcium will decrease as muscle contract which also leads to a decrease in contractility force
Can fibre-type composition be altered?
No, genetically determined so can only make use of the muscle fibres you have
Nutrition and exercise will not change the muscle fibres
