muscles Flashcards
Describe how muscles work
● Work in antagonistic pairs → pull in opposite directions eg. biceps / triceps
○ One muscle contracts (agonist), pulling on bone / producing force
○ One muscle relaxes (antagonist)
● Skeleton is incompressible so muscle can transmit force to bone
Describe the gross and microscopic structure of skeletal muscle
● bundles of muscle fibres (cells) packaged together
● Attached to bones by tendons
● Muscle fibres contain:
○ Sarcolemma (cell membrane) which folds inwards (invagination) to form transverse (T) tubules
○ Sarcoplasm (cytoplasm)
○ Multiple nuclei
○ Many myofibrils
○ Sarcoplasmic reticulum (endoplasmic reticulum)
○ Many mitochondria
Describe the ultrastructure of a myofibril
● Made of two types of long protein filaments, arranged in parallel
○ Myosin - thick filament
○ Actin - thin filament
● Arranged in sarcomeres
○ Ends – Z-line / disc
○ Middle – M-line
○ H zone – contains only myosin
Give an overview of muscle contraction
● Myosin heads slide actin along causing the sarcomere to contract
● causes myofibrils and muscle fibres to contract
● When sarcomeres contract (shorten)…
○ H zones get shorter
○ I band get shorter
○ A band stays the same
○ Z lines get closer
Describe the roles of actin, myosin, calcium ions, tropomyosin and ATP in
myofibril contraction
*Depolarisation spreads down sarcolemma via T tubules causing Ca 2+ release from sarcoplasmic reticulum, which diffuse to myofibrils
*Calcium ions bind to tropomyosin, causing it to move → exposing
binding sites on actin
*myosin head, with ADP attached, to bind to binding sites on
actin → forming an actinomyosin crossbridge
*Myosin pulling actin along myosin, (ADP
released) causing power stroke.
* ATP binds to myosin head causing it to detach from binding site
*Hydrolysis of ATP by ATP(hydrol)ase releases energy for myosin heads to return to original position and breaks bridge.
*Myosin reattaches to a different binding site further along actin
Process is repeated as long as calcium ion concentration is high.
During muscle relaxation:
*Ca 2+ actively transported back into the endoplasmic reticulum using energy from ATP
*Tropomyosin moves back to block myosin binding site on actin again → no actinomyosin cross bridges
Describe the role of phosphocreatine in muscle contraction
*A source of inorganic phosphate (Pi) → rapidly phosphorylates ADP to regenerate ATP
○ ADP + phosphocreatine → ATP + creatine
● Runs out after a few seconds → used in short bursts of vigorous exercise
● Anaerobic and alactic
What are the properties of fast twitch muscles
● Specialised for brief, intensive
contractions (eg. sprinting)
● Produce less ATP rapidly (mostly) from
anaerobic respiration
● Fatigues quickly due to high lactate
concentration
Whats the structure of fast twitch
● Low levels of myoglobin
● Lots of glycogen → hydrolysed to provide
glucose for glycolysis / anaerobic
respiration which is inefficient so large
quantities of glucose required
● High conc. of enzymes involved in
anaerobic respiration (in cytoplasm)
● Store phosphocreatine.
Whats the structure of slow twitch
● High conc. of myoglobin → stores
oxygen for aerobic respiration
● Many mitochondria → high rate of
aerobic respiration
● Many capillaries → supply high conc. of
oxygen / glucose for aerobic
respiration and to prevent build-up of
lactic acid causing muscle fatigue.
Whats the properties of slow twitch
● for slow, sustained
contractions (eg. posture, long
distance running)
● Produce more ATP slowly (mostly) from
aerobic respiration
● Fatigues slowly
