Blocked receptors at a nerve-muscle junction

In the picture

1. 1Nerve tip: releases small signalling molecules into the gap.
2. 2Synaptic gap: narrow space crossed by the signalling molecules.
3. 3Receptor on the muscle fibre: site where acetylcholine normally binds.
4. 4Blocked receptor: a molecule occupies the receptor so acetylcholine cannot bind.
5. 5Muscle fibre bands: stay smooth and slack because contraction is prevented.

Examples

• A muscle relaxant used during surgery keeps muscles still.
• A poisoned blowpipe dart can paralyse an animal by blocking muscle signals.

Quiz: Blocked receptors at a nerve-muscle junction (Age 16)

1. 1

   What does curare do at the nerve-muscle junction?

   • It increases acetylcholine release from the nerve tip.
   • It blocks acetylcholine receptors on muscle fibres.
   • It makes the synaptic gap disappear.
2. 2

   If acetylcholine cannot bind to receptors on a muscle fibre, what happens to the muscle?

   • It cannot contract and stays relaxed.
   • It releases more acetylcholine.
   • It contracts continuously.
3. 3

   According to the card, what happens when a molecule occupies a receptor?

   • The muscle fibre bands become tightly contracted.
   • Acetylcholine cannot bind to the receptor.
   • The nerve tip stops releasing signalling molecules.

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.