How muscle cells shorten

The idea

Muscle cells contain special proteins that change their shape and arrangement in response to nervous electrical impulses, giving the cells a shorter form so the muscle moves.

Muscle on the move

When a nerve impulse reaches a muscle, the muscle must move. A muscle is made of muscle cells.

How do you think a single muscle cell moves?

• Special proteins in it change their shape and arrangement
• The cell loses its nucleus
• The cell is squeezed by the bones

One muscle cell

Press Next step to watch one muscle cell.

Shape change, not magic

The cell does not shrink away. Its proteins take a new shape and a new arrangement, and so the whole cell becomes shorter.

Muscle cells contain special proteins that change their shape and arrangement in response to nervous electrical impulses. This gives the cells a shorter form, so the muscle moves.

Notes

Muscle cells have special proteins that change shape and arrangement in response to nervous electrical impulses, giving the cells a shorter form, so the muscle moves.

Check yourself

What do muscle cells contain that changes in response to nerve impulses?

What do the proteins change when an impulse arrives?

In this made-up example, a muscle cell is 100 units long at rest and 70 units long after the impulse. By how many units has it shortened?

Answer: 30

100 − 70 = 30 units shorter.

What happens to the muscle when its cells take a shorter form?

• Extra fluid-filled balloons. The fluid-filled balloon is around the brain. In muscle cells, special proteins change.
• Receptors for taste. Gustatory receptors are tips of nerve cells that detect taste. Muscle cells contain special proteins.
• Special proteins — correct. Yes!
• Both their shape and their arrangement in the cell — correct. Yes!
• Only their colour. The book says the proteins change both their shape and their arrangement.
• Their number, by dividing. The proteins change their shape and arrangement in response to the impulses.
• The muscle sends impulses. Nerve cells send impulses. When muscle cells take a shorter form, the muscle moves.
• The muscle moves — correct. Yes!
• The muscle makes hormones. The book says the shorter form of the cells makes the muscle move.