Muscles - A2 Flashcards
1
Q
Describe the structure of a skeletal muscle.
A
Compound of many muscle fibres bound together by connective tissue. Each muscle fibre is surrounded by a thin membrane called sarcolemma, containing nuclei. Cell contains many microfibrils, surrounded by sarcoplasmic reticulum. Microfibrils made up of myofilaments (actin). These are arranged into contractile units called sarcomeres.
2
Q
Describe the sliding filament theory of muscle action.
A
- calcium ions are released from sarcoplasmic reticulum
- calcium ions bind to troponin and cause tropomyosin to move, exposing the myosin head binding sites on the actin filament
- myosin heads bind to actin binding sites forming cross bridges
- each myosin head contains a molecule of ATP which hydrolyses into ADP + Pi by ATPase. This energy released causes nod action of myosin head, pulling the actin filament a short distance.
- a new ATP attaches to myosin head, breaking cross bridge and separating it from actin
- The process repeats moving the actin along a bit more each time
3
Q
Describe and explain the role of ATP and phosphocreatine in providing energy during contraction.
A
- phosphocreatine is store in muscle fibres for when ATP in muscle fibres runs out (4 seconds roughly)
- it generates ATP from ADP rapidly in aerobic conditions
- provides energy for muscle contraction
- phosphate is given to ADP hence phosphocreatine becomes creatine
4
Q
Describe and explain slow twitch muscle fibres.
A
- have lots of mitochondria
- respire aerobically to regenerate ATP
- high concentration of myoglobin for a very high affinity to oxygen which is stationary and stays in muscle
- closely associated with large number of capillaries to provide good oxygen supply
- less extensive sarcoplasmic reticulum as less calcium ions required at one time
- less glycogen as glucose broke fully down via aerobic respiration
5
Q
Describe and explain fast twitch muscle fibres.
A
- produce rapid, strong contractions but only sustained over short period of time
- thicker myosin, stronger heads
- have store of oxygen and glucose (x19 more ATP)
- anaerobic respiration - not much oxygen supply
- use phosphocreatine to regenerate ATP
- have fewer mitochondria
- lower concentration of myoglobin