Muscle ContractionHESI A2 cheat sheet

The sliding filament model

9 key facts 5 practice questions Reviewed Oct 2026

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The Proteins

Actin — thin filament
Myosin — thick filament with heads
They slide past each other; the filaments do not shorten

The Trigger

Nerve impulse → acetylcholine released at the neuromuscular junction
Calcium released from the sarcoplasmic reticulum
Calcium exposes the binding sites on actin

The Fuel

ATP is needed both to contract and to RELEASE
Without ATP the heads stay bound — this is rigor mortis

Unit

The sarcomere is the functional unit, Z line to Z line

Key takeaway

The sliding filament model

Before you read

Test yourself first: 5 questions

Question 1 of 5

The wave-like muscle contractions that move food through the digestive tract are called:

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