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15.1.1014-15 · Homeostasis and Control

Stimulating Contraction in Striated Muscle — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 7 parts Lesson 25 of 31 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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Lesson summary

15.1.10 Stimulating Contraction in Striated Muscle — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe how a motor neurone triggers calcium release and exposes the myosin-binding sites.Definition — the place where a nerve impulse arrives at a muscle cell.Stimul…

  • Neuromuscular junction
  • Sarcolemma
  • Sarcoplasmic reticulum
  • Tropomyosin
  • Stimulus — striated muscle contracts when it receives an impulse from a motor neurone
  • An impulse arrives at the presynaptic membrane of the motor neurone

Part 1 of 5The neuromuscular junction

Definition
  • Definition the place where a nerve impulse arrives at a muscle cell.
Stimulus
  • Stimulus striated muscle contracts when it receives an impulse from a motor neurone.

Part 2 of 5Events at the presynaptic membrane

1
An impulse arrives at the presynaptic membrane of the motor neurone.
2
The action potential causes Ca2+ to diffuse into the neurone.
3
Ca2+ stimulate vesicles containing acetylcholine (ACh) to fuse with the presynaptic membrane.
4
ACh is released into the junction.

Part 3 of 5Events at the muscle fibre

1
ACh diffuses across and binds to receptor proteins on the sarcolemma.
2
Ion channels in the sarcolemma open, so Na+ diffuse in.
3
The sarcolemma depolarises and an action potential passes down the T-tubules.
4
Voltage-gated Ca2+ channels in the sarcoplasmic reticulum open.
5
Ca2+ flood into the sarcoplasm around the myofibrils.

Part 4 of 5Exposing the binding sites

1
Ca2+ bind to troponin, which changes shape.
2
Troponin and tropomyosin change position on the thin actin filaments.
3
The myosin-binding sites on actin are exposed.
4
The sliding filament process can begin.

Part 5 of 5Comparison with cholinergic synapses

FeatureCholinergic synapseNeuromuscular junction
BetweenTwo neuronesNeurone and muscle
Postsynaptic membraneNeurone membraneSarcolemma
OutcomePostsynaptic action potentialAction potential down T-tubules, Ca2+ released

Key terms

TermMeaning
Neuromuscular junctionSynapse between a motor neurone and a muscle fibre.
SarcolemmaSurface membrane of a muscle fibre.
T-tubuleFold of the sarcolemma carrying action potentials inwards.
Sarcoplasmic reticulumStore of Ca2+ in muscle.
TroponinProtein on actin that binds Ca2+.
TropomyosinProtein blocking myosin-binding sites.

Avoid these mistakes

1
Mixing up the junction with a neurone-to-neurone synapse — this one is between a neurone and muscle.
2
Saying Ca2+ come from outside the fibre — they come from the sarcoplasmic reticulum.
3
Saying ACh enters the muscle — it binds to receptors.
4
Forgetting troponin and tropomyosin must move before myosin can bind.

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