Muscles Flashcards
What are the 3 types of muscles?
Smooth
Skeletal
Cardiac
Describe the structure of skeletal muscle?
Individual cells make up muscle fibers Fibers wrapped in CT sheaths Blood vessels in gaps between fibers Fibers contain myofibrils Striated
What are tendons made from?
CT
Continuation of the sheath covering muscle fibres
Describe the structure of a myofibril.
Sarcomere - repeating unit Z lines - boundary of sarcomere Thin actin filaments Thick myosin filaments Titin filaments
What are the purpose of titin filaments?
Guide for myosin filaments
Ensures actin + myosin filaments slide over each other
Describe what happens in contraction, in terms of actin, myosin, titin filaments, and the distances between them.
Titin shorten
Distance between actin filaments decreases
Distance between adjacent myosin filaments decreases
Describe the cross-bridge cycle.
4
1) Calcium released into sarcomere - [Ca2+] up - cross bridge binding sites on actin filament open - CB binds to actin
2) Cross bridge moves - ADP + Pi (from step 4) released
3) ATP binds to myosin - cross bridge detaches from actin
4) ATP hydrolyses energises cross bridge - ready to bind to actin
How does Calcium regulate the cross bridge cycle?
Tropomyosin + Tropinin on actin filaments
Cross bridge binding site blocked by tropomyosin - held in place my troponin
Ca2+ binds to troponin binding site - change in shape - pulls tropomyosin away - opens CB binding site
Why is the sarcoplasmic reticulum important in the cross bridge cycle?
Storage/release of Ca2+ into myofibrils
Why are transverse tubules present around myofibrils?
Takes surface depolarisation by motor neurone and channels it deep into the muscle fibres
Coordinated contraction
Why must Ca2+ be removed from the myofibril actively?
If [Ca2+] remained high, cross bridge binding site would remain open and muscle would not be able to relax
Remove Ca2+ = tropomyosin restores blocking action
What is the difference between isometric and isotonic twitches?
Isometric - shorter latent period but longer contraction event
Isotonic - longer latent period but fast contraction event
Describe what summation of contractions is?
Rapid repeated AP’s
Maintains high [Ca2+]
Cross bridge binding sites remain open
Constant stimulus (fused tetanus)
Sum of the length-tension relationship of muscle contraction.
Too stretched = not enough overlap = less tension
Too squashed = interference between filaments
Muscle length for optimal tension = optimal length
Why does summation not occur in cardiac muscle?
Heart muscles must relax in between strokes or you’ll bloody die wont you
Why do muscles fatigue?
Stops ATP from being used up
This stops muscles from not being able to activate new cross bridge cycles