Contraction of a skeletal muscle Flashcards
If muscles cannot “push”, how do they move a body in different directions?
Work in antagonistic pairs that contract and relax
What mechanism is used in the contraction of a muscle?
The sliding filament mechanism
What is the evidence for the sliding filament mechanism?
In a sarcomere,
I band becomes narrower
Sarcomere shortens/ Z lines move closer together
H zone becomes narrower
What is myosin made up of?
A fibrous protein tail
A globular protein head
What 3 proteins are used in the sliding filament mechanism?
Myosin
Actin
Tropomyosin
What are the 3 stages of the sliding filament mechanism?
Muscle stimulation
Muscle contraction
Muscle relaxation
Process of muscle stimulation
Action potential reaches neuromuscular junction, causing Ca2+ channels to open
Calcium ions cause vesicles to fuse with membrane and release acetylcholine into synaptic cleft
Acetylcholine diffuses across cleft and binds with receptors on muscle cell membrane, causing depolarisation
Process of muscle contraction
Action potential travels through t tubules to sarcoplasmic reticulumn, opening calcium channels that diffuse out into sarcoplasm
Calcium ions cause tropomyosin to change shape, exposing binding sites on actin filament
ADP on myosin heads bind and form cross bridges with actin
This causes myosin head to change their angle, pulling the actin and releasing ADP
An ATP attaches to the myosin head, causing the cross bridge to break
Calcium ions activate ATPase, causing the Pi to break off to form ADP
ATP hydrolysis energy release causes myosin head to revert back to original angle
Myosin head will reattach further along actin filament
Occurs on both ends of the Myosin
Process of muscle relaxation
When nervous stimulation ceases, Ca2+ actively transported back into SR using ATP
This causes tropomyosin to block actin binding sites
Myosin can no longer bind
