IB Biology Topic B3.3.2 Sliding Filament Model of Muscle Contraction Revision Notes (HL)

IB Biology Topic B3.3.2 Sliding Filament Model of Muscle Contraction Revision Notes (HL) | RevisionDojo

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Sarcomeres Shorten as Actin and Myosin Slide Past Each Other

Definition

Sarcomere

A sarcomere is the basic contractile unit of muscle fiber.

The sarcomere is built from several parts:
1. Z-discs (Z-lines): define the sarcomere boundaries and anchor the thin filaments.
2. Thin filaments (actin): extend from the Z-discs toward the sarcomere centre.
3. Thick filaments (myosin): occupy the central region and interlock with actin.
4. I-bands: light bands containing only actin.
5. A-bands: dark bands spanning the full length of the myosin, including where it overlaps actin.
6. H-zone: the central part of the A-band with only myosin when the muscle is relaxed.
During contraction the Z-discs are pulled closer together, shortening the sarcomere.

Note

The sarcomere shortens because the actin and myosin filaments slide past each other.
The filaments themselves do not change length.

The Sliding Filament Mechanism Works in a Repeating Cycle

Cross-bridge formation
1. Myosin heads attach to binding sites on actin, forming cross-bridges.
2. This is triggered by Ca²⁺ release following a nerve impulse.
Power stroke

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Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

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Sarcomeres Shorten as Actin and Myosin Slide Past Each Other

Definition

Sarcomere

A sarcomere is the basic contractile unit of muscle fiber.

The sarcomere is built from several parts:
1. Z-discs (Z-lines): define the sarcomere boundaries and anchor the thin filaments.
2. Thin filaments (actin): extend from the Z-discs toward the sarcomere centre.
3. Thick filaments (myosin): occupy the central region and interlock with actin.
4. I-bands: light bands containing only actin.
5. A-bands: dark bands spanning the full length of the myosin, including where it overlaps actin.
6. H-zone: the central part of the A-band with only myosin when the muscle is relaxed.
During contraction the Z-discs are pulled closer together, shortening the sarcomere.

Note

The sarcomere shortens because the actin and myosin filaments slide past each other.
The filaments themselves do not change length.

The Sliding Filament Mechanism Works in a Repeating Cycle

Cross-bridge formation
1. Myosin heads attach to binding sites on actin, forming cross-bridges.
2. This is triggered by Ca²⁺ release following a nerve impulse.
Power stroke

Definition

Paywall

(on a website) an arrangement whereby access is restricted to users who have paid to subscribe to the site.

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Note

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam quis nostrud exercitation.

Excepteur sint occaecat cupidatat non proident

Tip

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

IB Biology Topic B3.3.2: Sliding Filament Model of Muscle Contraction Notes

Sarcomeres Shorten as Actin and Myosin Slide Past Each Other

The Sliding Filament Mechanism Works in a Repeating Cycle

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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Sarcomeres Shorten as Actin and Myosin Slide Past Each Other

The Sliding Filament Mechanism Works in a Repeating Cycle

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics