Muscle Contraction and Sarcomere Structure

Vocabulary flashcards covering muscle contraction, sarcomere structure, and related proteins.

Muscle Contraction Initiation

The process initiated when an action potential reaches a muscle, leading to depolarization.

Neurotransmitter

A chemical messenger that binds to receptors on the muscle membrane, causing depolarization.

Sarcoplasmic Reticulum

The organelle that releases calcium ions (Ca2+) during muscle contraction.

Troponin

A protein that binds to Ca2+, causing a conformational change in tropomyosin.

Tropomyosin

A protein that blocks actin binding sites when the muscle is relaxed.

Cross Bridge Cycle

The cycle involving ATP binding, hydrolysis, and the movement of myosin heads to cause muscle contraction.

ATP Binding to Myosin Head

The event that breaks the bridges between actin and myosin.

Cocked Position

The position of the myosin head when it's ready to bind to an actin site.

Pi Loss from Myosin Head

The event that forms a cross bridge between actin and myosin.

Power Stroke

The event where myosin swivels and pulls actin towards the center of the sarcomere.

Titin

The protein that recoils during muscle relaxation.

Antagonistically

The way muscles work in pairs, contracting while the other expands.

Sarcomere

The functional unit in muscles, a repeating unit in all muscle fibers.

Myosin

The thick filament in the middle of the sarcomere, possessing myosin heads.

Actin Fibers

The thin filaments in the sarcomere.

Z Band

The anchoring point on the sarcomere for actin and titin.

Muscle Contraction (Sarcomere Level)

The result of thick myosin filaments pulling thin actin filaments.

I Bands (Light Bands)

The area within the sarcomere that gets narrower during muscle contraction.

Titin

An anchoring protein that acts like a spring and attaches to the Z band.

Titin Recoil

The role of titin in muscle relaxation.

Steps

1. Action potential reaches muscle

2. neurotransmitter binds to the receptor and depolarises the membrane

3. Calcium ions produced from the sarcoplasmic reticulum

4. Calcium ions bind to troponin - causes a conformational change in tropomyosin (opens actin binding sites)

5. ATP binds to the myosin head (breaks bridges)

6. ATP hydrolysis into ADP + Pi (myosin head in cocked position and ready to bind)

7. Lose Pi from the myosin head = cross bridge between actin binding site and myosin

8. Lose ADP from the myosin head = power stroke occurs (myosin swivels and pulls the actin towards the centre of the sarcomere)

9. Calcium diffuses out, troponin + tropomyosin block binding sites

10. Titin recoils and muscle relaxes