muscle structure Flashcards
- Describe the gross structure of muscle.
- Cells are fused together into muscle fibres * Muscle fibres share nuclei and cytoplasm called sarcoplasm * Within the sarcoplasm is a large concentration of mitochondria and endoplasmic reticulum (called sarcoplasmic reticulum) * Many myofibrils run through the cytoplasm-they are made of two protein myofilaments called actin and myosin.
- Label the parts of a muscle fibre show below:
- Sarcolemma (cell surface membrane) 2. Sarcoplasm (cytoplasm) 3.Myofibrils (made of actin and myosin) 4. Sarcoplasmic reticulum 5. Nucleus 6. Nucleus (muscle fibres are multinucleate) 7. myofilament (acin or mysoin) 8. Mitochondria
- Draw and label the microstructure of a
myofibril.
4.Why does an electron micrograph of a sarcomere show a banded pattern of light and dark regions?
I band-light stripes contain actin filaments, changes length based on actin and myosin overlap, anchored at Z line
A band-dark stripes contain actin and myosin filaments, remains the length of myosin filaments
H zone- a lighter zone in the middle of the dark stripe, contains myosin filaments only, changes length depending on actin and myosin overlap
Z-line- found in the middle of I bands, this is wheee actin filaments are anchored and represents start and end of sac Romero
M-line-only seen on some diagrams. A line in the middle of A band, where myosin filaments are anchored
Sarcomere- repeating functional unit of myofibril from one Z-line to next, c(angles length depending on myosin and actin overlap
- What is the role of glycogen in the muscles?
Energy storage polysaccharide. To be available for hydrolysis to release glucose for respiration to provide ATP
- Describe the role of calcium ions in muscle
contractions.
Calcium ions diffuse into myofibrils from sarcoplasmic reticulum, Calcium ions cause movement of tropomyosin on actin, This movement causes exposure of the binding sites on the actin, Myosin heads attach to binding sites on actin forming an actin-myosin crossbridge.
- Describe the role of ATP in muscle
contractions.
Hydrolysis of ATP on myosin heads causes myosin heads to bend, Bending pulls actin molecules towards the M-line (middle of sarcomere), attachment of a new ATP molecule to each myosin head causes myosin heads to detach from the binding site on actin (breaks the actin-myosin crossbrige).
- What are the names of the 3 proteins
involved in muscle contractions? Describe their structures.
Actin – 2 thin twisted proteins. Myosin – Thick filament, with rod shaped tails and bulbous heads. Tropomyosin – twists round actin.
- Explain why the myosin heads have ATPase
hydrolysis of ATP, muscle contraction requires energy / ATP, Use of ATP by myosin.
- What is the role of phosphocreatine in
muscle contraction?
In anaerobic conditions it provides phosphate to ADP to make ATP . Muscles have a very limited store of phosphocreatine so it only produces a small amount of ATP.
- What happens to the lengths of the I-band and A-band during muscle contraction?
I-band length decreases, while A-band does not change
- Where are mitochondria found in muscles?
Around the outside of the sarcomere, for a short diffusion pathway, ensuring fast diffusion of oxygen for aerobic respiration
- What does antagonistic mean?
Muscles work in opposite directions
- How does arrival of an action potential at a neuromuscular junction result in muscle
contraction?
- Action potential arrives at the axon terminal of the presynaptic neurone * Voltage gated calcium ion channels open and calcium ions diffuse into the synaptic knob * Vesicles of acetylcholine/neurotransmitter fuse with the presynaptic membrane * Acetylcholine/Neurotransmitter is released by exocytosis into the synaptic cleft * Neurotransmitter diffuses across the cleft * Neurotransmitter binds to receptors on the sarcolemma * sodium ion channels open * sodium ions move into the muscle cell * cell membrane depolarises * the t-tubule transmits the depolarisation to the sarcoplasmic reticulum * The sarcoplasmic reticulum release calcium ions into sarcoplasm (cytoplasm) which cause tropomyosin to move and allow actin-myosin cross bridges to form
- Compare fast and slow twitch muscle fibres
Fast fibres have little blood capillaries, slow fibres have lots of blood capillaries. Fast fibres have a short contraction-relaxation cycle whereas slow fibres have long contraction-relaxation cycles. Slow twist fibres stores phosphocreatine, slow fibres have lots of mitochondria. Fast twitch fibres get most of ATP from anaerobic respiration, therefore fatigue easily due to large amounts of lactate, slow twitch fibres get most ATP from aerobic respiration so don’t fatigue easily. Fast twitch fibres are found in upper arms and for small bursts of energy and slow twitch fibres are found in calf’s and needed to keep you in an upright position all day.
