3.6.3 Skeletal Muscles As Effectors Flashcards
What’s skeletal muscle
Attached to bone, under conscious control
What makes up a muscle and it’s ultra structure
Myofibrils, lots of muscle fibres that share nuclei and cytoplasm (sarcoplasm), lots of mitochondria
How does a muscle create movement
Act in antagonistic pairs against skeleton, when one contracts the other relaxes, can be automatic or conscious
Microscopic structure of skeletal muscle
Muscle is made of myofibrils
Myofibrils contain
Actin, thin protein
Myosin, thick protein, heads at the end
I band (light), only actin, no overlap
A band (dark), actin and myosin, overlap
H zone, centre of A band
Z line, centre of I band
Distance between two Z lines is the sarcomere
What’s tropomyosin
Forms fibrous filaments around actin filament
What can explain muscle contraction
Sliding filament mechanism
What happens to Myofibrils during muscle contraction
I band becomes narrower
Sarcomere shortens
H zone becomes narrower
A band remains same width
How do actin and myosin filaments slide past eachother
Head of Myosin filament form cross bridges with actin filament, attach to binding site on actin filament and flex, actin filaments pulled along myosin filaments, they detach, return to their original angle and reattach to actin further along using ATP to release energy,
What are the stages of the sliding filament theory
Muscle stimulation, muscle contraction, muscle relaxation
What happens during muscle stimulation
Action potential releases neuromuscular junctions, Ca2+ protein channels open, it diffuses into synaptic knob, synaptic vesicles to fuse with Presynaptic membrane releasing acetylcholine into synaptic cleft, acetylcholine diffuses across synaptic cleft, binds to receptors on muscle cell surface membrane, depolarisation occurs
What happens during muscle contraction
Action potential travels deep into muscle fibres through t tubules, these tubules are in contact with sarcoplasmic reticulum actively transporting Ca2+ into muscle (low conc in cytoplasm), action potential opens Ca2+ protein channels on sarcoplasmic reticulum causing Ca2+ to diffuse back into cytoplasm down a conc gradient, Ca2+ causes tropomyosin molecules which were blocking binding sites to pull away, ADP molecules attached to myosin heads allow it to bind to actin filament forming a cross bridge called actinomyosin bridge, myosin heads change their angle pulling actin filaments along, releasing ADP, ATP attached to myosin head causing it to detach from actin filament, Ca2+ activates enzyme ATPase hydrolyses ATP into ADP this provides energy for the myosin head to return to its original position, myosin head attached to ADP reattaches further along the actin filament and repeats as long as Ca2+ concentration in myofibril is high, myosin molecules are attached in two opposite facing sets the actin they are attached to move in opposite directions, they are pulled towards each other, decreases distance between two Z lines
What happens during muscle relaxation
Nervous stimulation stops, Ca2+ actively transported back into sarcoplasmic reticulum using energy from hydrolysis of ATP, re absorption of Ca2+ allows tropomyosin to block actin filament again, myosin heads are unable to bind to actin filaments, muscles relaxes,
What is ATP used for during muscle contraction
Hydrolysis of ATP to ADP releases energy for movement of myosin heads and reabsorption of Ca2+ into sarcoplasmic reticulum by active transport
What’s the role of phosphocreatine in muscle contraction
Doesn’t supply energy directly to muscle
Regenerates ATP, stored in muscle as a reserve supply of phosphate, available to combine with ADP immediately
When muscle is relaxed phosphocreatine store is replenished using phosphate from ATP
Two types of skeletal muscle fibres
Slow and fast
