One motor neuron supplies 120 muscle fibres…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
One motor neuron supplies muscle fibres. A small muscle has motor units, and each unit has fibres.
- How many fibres contract when motor units are active?
- How many fibres does the whole muscle have?
- What share of the fibres contracts in part (a)? Give the answer as a fraction of the muscle, in per cent.
Need a reminder? The key ideaShow
The signal goes from the central nervous system along a motor neuron to the neuromuscular junction. Acetylcholine makes an action potential in the sarcolemma, which spreads through the fibre and releases Ca from the sarcoplasmic reticulum. The calcium binds to troponin and unmasks the sites on the actin. A motor unit is a motor neuron with all the fibres that it supplies.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. fibres in a unit, units, units active.
Plan. Multiply the number of units by the fibres in a unit.
Step 1. fibres contract.
Step 2. fibres in all.
Step 3. Share: . This is also of the muscle.
Answer: fibres; fibres; .
Check. of the units are active, which is one third.
Watch out. In real muscles the units differ in size. These numbers are chosen for practice.
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