5: Muscles Flashcards
Two types of protein filament in myofibrils
actin, thinner and consists of two strands twisted around one another
myosin, thicker and consists of long rod-shaped fibres with bulbous heads that project to the side
What are the two bands in myofibrils
Anisotropic band - dark, where actin and myosin overlap
Isotropic band - light, where theres only actin
Describe the H zone the Z line
H zone - at the centre of the A band where there is only myosin
Z line at the centre of each I band
What is one sarcomere?
The distance between two adjacent Z lines
How are slow twitch muscle fibres adapted?
Adapted to aerobic respiration to prevent the build up of lactic acid as used in endurance
- large store of myoglobin (bright red and stores oxygen)
- supply of glycogen to provide a source of metabolic energy
- rich blood supply
- numerous mitochondria to supply ATP
How are fast twitch muscle fibres adapted?
- thicker and more numerous myosin filaments
- higher concentration of enzymes involved in anaerobic respiration
- a store of phosphocreatine
Describe the role of neuromuscular junctions
- when a nerve impulse reaches them they release acetylcholine in the synaptic cleft
- increases permeability to sodium ions in the post synaptic knob
- causes muscle contraction
Why are there numerous mitochondria in the sarcoplasm?
Muscles require ATP for the cross bridge cycle
In what 3 ways does a sarcomere change during contraction?
I band becomes narrower
Z lines move closer together
H zones becomes narrower
A band remains the same width
3 steps of muscle stimulation
- action potential reaches many nm junctions simultanesouly, causing Ca2+ ions to move into synaptic knob
- vesicles fuse with membrane and acetylcholine released into cleft
- acetylcholine diffuses across cleft and binds to receptors causing post-synaptic membrane to depolarise
3 steps in making the actin binding site available
Ca2+ ions released from ER
Ca2+ binds to troponin which changes shape
this pushes tropomyosin away from binding site
Role of calcium ions in muscle contraction x3
stimulate vesicles to fuse and release acetylcholine
bind to troponin to free binding site
activate enzyme ATPase, in cross bridge cycle
3 steps in muscle relaxation
nervous stimulation ceases, Ca2+ ions actively transported back to ER
tropomyosin moves back over binding site
myosin heads unable to bind, contraction ceases
Cross bridge cycle x6
- myosin head attaches to bind site
- head of myosin changes shape, pulling actin along, ADP released
- ATP attaches to myosin head, myosin detaches
- hydrolysis of ATP provides energy for myosin heads to resume its normal position
- head of myosin reattaches to a binding site further along
- cycle repeats
2 uses of ATP in muscle contraction
the movement of myosin heads
reabsorption of calcium ions into the ER by active transport
