Muscle Structure And Sliding Filament Theory Flashcards
What is the Epimysium?
> Layer of connective muscle tissue surrounding the muscle
protects the muscle from friction against other muscles and bones
forms muscle tendons
What are fasicles?
> Bundle of muscle fibres surrounded by perimysium
Each contains 10-100 muscle fibres
What are myofibrils?
> long contractile elements of muscle fibres
contains sarcomeres
What is a sarcoplasmic reticulum?
> Network of tubules and channels
calcium is stored for contractions
What is a sarcolemma?
> cell membrane surrounding a muscle fibre
What are transverse (t) tubules?
> where nerve impulses travel
What are sarcomeres?
> functional repeating segments of myofibrils
contains contractile proteins (actin and myosin)
What is actin?
> thin protein filaments found in myofibrils
contain active binding sites
work with myosin during muscle contractions
What is myosin?
> thick protein filaments found in myofibrils
protrusions known as myosin heads
works with actin during muscle contractions
What is tropomyosin?
> globular proteins
molecules wound around actin filaments
move to expose actins active binding site to allow cross-bridge formation
What is troponin?
> attached to tropomyosin
ca2+ binds to to facilitate tropomyosin to move
Describe the process of the sliding filament theory
> ca2+ is released from sarcoplasmic reticulum
ca2+ binds to troponin molecule on actin
tropomyosin moves, exposing actin binding sites
myosin heads form a cross-bridge with actin
breakdown of ATP releases energy for a power stroke (actin is pulled over myosin towards centre of sarcomeres)
cross-bridge is broken when new ATP molecule binds to myosin head
cycle repeats in a ratchet mechanism as long as there is sufficient ATP and ca2+
What occurs during the sarcomere during a muscle contraction?
> Z lines move closer together (sarcomere shortens)
H zone shortens/disappears
A band remains the same length
I band shortens
What are the five stages of muscle contraction?
- Resting
- Excitation
- Contraction
- Recharge
- Relaxing
Describe the resting Tate of muscle contraction
Prior to contraction, the muscle fibre is in a resting state, before there is any tension
Describe the excitation stage of muscle contraction
The muscle is stimulated with an electrical charge
Describe the contraction stage of a muscle contraction
The action of actin and myosin sliding past each other to bind and form a cross-bridge in a power stroke/ ratchet mechanism, causing the fibre to shorten
Describe the recharge stage of a muscle contraction
ATP is resynthesised, so that the cycle is repeated - (contraction is only repeated when ATP and ca2+ are sufficient)
Describe the relaxing stage of a muscle contraction
When stimulation of the nerve stops, actin and myosin unbind, and calcium returns to the sarcoplasmic reticulum
