B.1.3SL + HL
Muscular function
Guiding question: How do nerves and muscles work together to produce the right amount of force at the right time?
Learn it, then try it
Read each idea, work through its activities, then tick it off. 0 of 2 done.
B.1.3.1
Motor units and types of contraction
A motor unit is one motor neuron and the fibres it supplies; when stimulated, all its fibres contract fully. Units differ in fibre type (I, IIa, IIx) and neuron size, and are recruited roughly in that order as force demand rises. Contraction needs ATP, and hypertrophy or atrophy alters recruitment patterns. Contractions are isometric, isotonic concentric, isotonic eccentric or isokinetic. Agonist and antagonist pairs work together through reciprocal inhibition.
Match the terms
Key terms
Match each term to its meaning.
Tap a term, then tap its meaning.
Check yourself
Quick check
1.During the lifting phase of a biceps curl, which type of contraction occurs in the biceps brachii?
2.Which statements describe type I motor units? I. They have small motor neurons. II. They are highly resistant to fatigue. III. They produce the greatest force.
3.During the lifting phase of a dumbbell curl, which muscle is the agonist at the elbow?
B.1.3.2 · HL only
Sliding filament theory
A nerve impulse causes calcium ions (Ca²⁺) to be released from the sarcoplasmic reticulum. Ca²⁺ binds to troponin, which shifts tropomyosin off the binding sites on actin, so myosin heads attach and form cross-bridges. Each head then pivots in a power stroke, pulling actin towards the M line. A new ATP binds to break the cross-bridge, and splitting it re-cocks the head ready to reattach. Repeated cycles draw the Z discs closer together, so the sarcomere shortens.
Match the terms
Key terms
Match each term to its meaning.
Tap a term, then tap its meaning.
Check yourself
Quick check
1.Which occurs during concentric muscle contraction?
2.In the cross-bridge cycle, what must bind to a myosin head for it to detach from actin?
3.When a muscle fibre is stimulated, from where are calcium ions (Ca²⁺) released?
Practise this topic
Self-marking exam-style questions with Guide me hints and full mark schemes.
Links to other topics
- A.2.2How might poor nutrition reduce how well muscles work?
- B.1.4, B.2.1Why might a sprinter with mostly type IIx fibres produce force differently from a marathon runner with mostly type I fibres?
- A.2.2.1, A.2.2.2How can knowing how muscles contract guide what athletes eat, and when, for performance and recovery?