| Antagonistic muscles and how they work | - Skeletal muscle works in antagonistic pairs
- These pairs pull in opposite directions + when 1 is contracted + the other is relaxed
- Muscles cannot push they can only pull |
| When a muscle contracts what changes occur to the sacromere | - The I-band becomes narrower
- The Z-lines move closer together or in other words the sacromere shortens
- The H-zone becomes narrower
- A band = remains the same |
| 3 main proteins that are involved in the sliding filament mechanism | - Myosin
- Actin
- Tropomyosin |
| Myosin | - Made up of 2 types of protein
- A fibrous protein filament (tail)
- A globular protein formed into 2 bulbous structures at 1 end (the head) |
| Actin | - Globular protein arranged into a helical strand |
| Tropomyosin | - Fibrous strand wound around actin filaments |
| SFM - Muscle stimulation (1) | - An AP travels into the muscle fibre via T-tubules, which are in contact with the SR
- As AP reaches the SR, cal ions channels open
- Cal ions diffuse into SR |
| SFM - Muscle stimulation (2) | - Cal ions released from SR, binds to troponin
- Causes tropomyosin mol to move, exposing myosin binding site on actin filament
- Now myosin + actin can bind to form cross-bridge |
| SFM - Muscle contraction (1) | - Myosin head attaches to actin to form a cross bridge (calcium ions must
be present) |
| SFM - Muscle contraction (2) | - ADP + Pi are released from the myosin
- This causes a POWER STROKE (ACTIN slides past) |
| SFM - Muscle contraction (3) | - ATP binds to the myosin head causing the cross bridge to release |
| SFM - Muscle contraction (4) | - ATP is broken to ADP + Pi
- This energy release cocks the myosin head (recovery stroke) |
| SFM - Muscle relaxation | - Ca2+ absorbed back into the SR
- Tropomyosin reverts to orginal shape, blocks actin binding sites
- Contraction stops |
| Phosphocreatine | - Cannot supply energy directly to the muscle
- Supplies phosphate, which is available immediately to combine w/ADP + so reform ATP
- Store is replenished using phosphate from ATP when muscle is relaxed |
| Roles of tropomyosin and calcium ions | - Ca2+ causes tropomyosin to be displaced
- So it no longer blocks the myosin binding site
- So myosin and actin can bind together allowing bridge cycling |
| Role of ATP | - Needed to actively transport Ca2+ into tropomyosin
- When the muscle relaxes Ca2+ are actively transported back into the sacroplasmic reticulum (need ATP)
- Binds to myosin head causing it to detach, hydrolysed into ADP+Pi causing cock and attach of myosin head |
