Unit 9 - Muscles Flashcards
Overview of how muscles work?
Muscles act in antagonistic pairs. They move bones at a joint and are attached to bones by tendons. To produce movement, muscles contract against an incompressible skeleton.
Why are muscles antagonistic pairs?
When one muscles contracts the other of the pair relaxes.
Ultrastructure of skeletal muscle?
Muscle fibre structure?
Structure of a sarcomere?
What type of filament is actin?
Thin filament
What type of filament is myosin?
Thick filament
Where is the H zone?
Gaps between the actin
Where is the I band?
Between the z line and the myosin
Where is the A band?
Spans the length of the myosin
Myofibril under an electron microscope?
Under an electron microscope what bit is the lightest region?
Actin only as it is thinner than Myosin. (I band)
Under an electron microscope which bit is the darkest region?
The actin and myosin overlapping. (A band)
Under an electron microscope which bit is the in between region?
The myosin only. (H zone)
What happens to the zones and bands when a muscle contracts?
-Thick and thin filaments slide between each other. H zone gets shorter. I band gets shorter. A band stays the same.
Overview of the sliding filament theory?
It is when muscles contract. The actin filaments slide over the myosin filaments.
What are thin filaments made from?
Actin plus tropomyosin
What are thick filaments made from?
Consist of many myosin molecules. Each myosin is made of a tail and a head.
Stages of myofibril contraction/sliding filament theory?
- Action potentials depolarise the sarcolemma and T-tubules
- Voltage gated calcium ion channels on the sarcoplasmic reticulum membrane open.
- Calcium ions diffuse from sarcoplasmic reticulum into the myofibril
- (By binding to troponin which are calcium ion receptors), calcium ions cause the tropomyosin to move, exposing myosin binding sites on the actin.
- Myosin heads bind actin forming actinomyosin bridges
- Calcium ions activate ATP hydrolase
- Energy from hydrolysis of ATP causes myosin heads to bend and pull the actin
- Attachement of ATP to the myosin heads causes them to detach from actin
- Myosin heads move back to their original position and reattach at binding sites further along the chain.
What is phosphocreatine?
It is stored in muscle. It donates a phosphate to reform ATP quickly, from ADP + Pi, in anaerobic conditions. When the muscle is relaxed, creatine is phosphorylated back to phosphocreatine using Pi from ATP made in respiration.
What are slow twitch fibres adapted for?
Aerobic respiration (endurance)
What are fast twitch fibres adapted for?
Anaerobic respiration (quick, more powerful contractions)
How are slow twitch fibres adapted?
-Contract slowly, with less powerful contractions
-Adapted for aerobic respiration to prevent lactic acid build up and muscle fatigue
-Have a large store of myoglobin (molecule which can store oxygen)
-Many mitochondria
-Adapted for long-term/endurance work such as standing and marathon running
-Very closely associated with a large number of capillaries (shorter diffusion pathway/larger surface area).
How are fast twitch fibres adapted?
-Have a high concentration of enzymes for anaerobic respiration
-Contract rapidly with short powerful contractions
-Adapted for short term, intense exercising such as sprinting
-Have a store of phosphocreatine, to provide phosphate to generate ATP quickly
-Have a large store of glycogen (store of glucose) so anaerobic respiration can happen more readily as it is less effective than aerobic (2ATP compared to 38ATP)
-Have thicker more numerous myosin fibres
-Less mitochondria, less blood vessels, less myoglobin.
