Muscle 1 Flashcards
What are the 2 subclasses of muscle?
- Striated
- Smooth
What kind of muscles are striated?
- Skeletal (involuntary muscles)
- Cardiac
Where would you find smooth muscle?
- Blood vessels
- Vas deferens
- Airways
- Uterus
- GI tract
- Bladder
- etc..
What is a skeletal muscle cell?
- Muscle fibre
- Multinucleate
Describe the growth and repair of skeletal muscle.
- Form in utero from mononucleate myoblasts
- Increase fibre size during growth
- Myoblasts do not replace cells if damaged
- Satellite cells replace cells after injuryWhat do sate
What are muscles?
Bundles of fibres encased in connective tissue sheaths
What do tendons do?
Attach muscle to bone
What do satellite cells do?
Differentiate to from new muscle fibres
What do other fibres do to compensate when muscle fibres are injured?
Undergo hypertrophy
What is the A band?
Stretch of myosin filament
What is the H zone?
Space between ends of actin filaments
What happens during muscle contraction?
- Muscle shortens
- Myosin stays same length
- Space between actin filaments decrease
- Space between myosin filaments decrease
What is the I band?
Space between ends of myosin filaments
What is a cross bridge?
ATP binding site on myosin filament
How does tension develop?
Through contraction of muscle
What are the stages in the cross-bridge cycle?
- Cross bridge binds to actin
- It drags actin along the myosin filament
- ATP binds to Myosin
- Myosin detaches and cross bridge returns to original position
Describe the role of troponin, tropomyosin and calcium ions in muscle contraction.
-Tropomyosin partially covers the myosin binding sites on actin.
Tropomyosin is held in this position by troponin which acts as a cooperative block.
-When calcium binds to troponin it causes a conformational change which pulls tropomyosin away and allows myosin to bind to actin.
What is a motor unit
Motor neurons
+
muscle fibres
Tension
Force exerted by muscle
Load
Force exerted on muscle
Isometric
Contraction with constant length
Isotonic
Contraction with shortening length
Lengthening
Contraction with increasing length
What causes a twitch?
A single action potential sent to a muscle fibre
What is the latent period?
The time before the excitation contraction starts
When does the contraction time occur?
Between start of tension and time when we have peak tension
What is contraction time dependent on?
Calcium ion concentration
Describe the latent period and contraction event of isometric contraction?
- Shorter latent period
- Longer contraction event
What happens as load increases?
-Contraction velocity and distance shortened decreases
Summation
Addition of AP to give waves with greater amplitude
Describe the AP of tetanus.
AP is 1-2 ms long but twitch can last up to 100ms
Tetanus
Sustained level of tension in a given period of time
Unfused tetanus
AP continue to rise and fall when recorded on graph
Fused tetanus
APs are so frequent there is no repolarisation
Why is tetanic tension greater than twitch tension?
[Ca] never gets low enough to allow troponin/ tropomyosin to re-block myosin binding sites
What are the length tension relationships/
- Less overlap of filaments= less tension
- Too much overlap of filaments=filaments interfere with each other
- Muscle length for greatest isometric tension=optimal length
What does movement around a limb require?
2 antagonistic groups of muscles (1 flexes, the other straightens)
What does the lever system of muscles do?
Amplifies muscle shortening velocity producing increased manoeuvrability
