Sliding Filament Segment

In the picture

1. 1The whole muscle belly.
2. 2One long fibre extending from the muscle belly.
3. 3The upper close-up segment with thick pink rods and thin blue rods spread apart.
4. 4The lower close-up segment where the rods overlap closer and small bridges touch between them.

Examples

• Bending your elbow to lift a backpack.
• Closing your fingers to grip a pencil.

Quiz: Sliding Filament Segment (Age 15)

1. 1

   What is the main cause of muscle fibre shortening during contraction?

   • The thin protein strands slide over the thick protein strands, making each repeating unit shorter.
   • The thick protein strands dissolve, so the repeating units collapse.
   • The whole fibre bends into a tight coil without the strands sliding.
2. 2

   When a muscle fibre contracts, what happens to the amount of overlap between the thick and thin protein strands?

   • It decreases, because the strands pull apart.
   • It increases, because the thin strands slide further over the thick strands.
   • It stays exactly the same, because only the bridges move.
3. 3

   If many repeating units along a muscle fibre shorten at the same time, what is the result for the fibre?

   • The fibre lengthens as a whole.
   • The fibre stays the same length but becomes wider.
   • The fibre shortens as a whole.

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.