How does the sarcoplasmic reticulum contribute to muscle contraction?

  1. The sarcoplasmic reticulum stores calcium ions (Ca2+)
  2. The action potential travels along the sarcolemma via the T tubules, which are connected to the sarcoplasmic reticulum
  3. When the action potential reaches the sarcoplasmic reticulum, Ca2+ channels open
  4. Ca2+ flows into the sarcoplasm, stimulating muscle contraction

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What happens when a nerve impulse reaches a neuromuscular junction?

  1. Calcium ion (Ca2+) channels open and Ca2+ flows into the end of the neurone
  2. This triggers the release of acetylcholine from vesicles
  3. Acetylcholine binds to receptors on the sarcolemma
  4. Sodium ion channels open and the sarcolemma depolarises
  5. Acetylcholinesterase breaks down acetylcholine to prevent overstimulation
  6. Depolarisation of sarcolemma spreads along T tubules towards the sarcoplasmic reticulum

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What is a neuromuscular junction?

A neuromuscular junction is the point where a motor neurone meets a skeletal muscle fibre.

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Why are there many neuromuscular junctions along a muscle?

Multiple neuromuscular junctions ensure rapid and coordinated muscle contraction, allowing all muscle fibres in a muscle to contract simultaneously.

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What is a motor unit?

A motor unit consists of all muscle fibres supplied by a single motor neurone and acts as a single functional unit, providing control over muscle force.


To exert a strong force, a large number of motor units are stimulated, whereas a small force requires the stimulation of only a few motor units.

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What provides the energy for the reformation of acetylcholine in the neurone?

The mitochondria found in the neurone provide the energy for the reformation of acetylcholine.

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What are the similarities between neuromuscular junctions and cholinergic synapses?

  1. Both use neurotransmitters transported by diffusion
  2. Both involve receptors causing an influx of sodium ions
  3. Both use the sodium-potassium pump for repolarisation
  4. Both use enzymes to break down the neurotransmitter

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What role does acetylcholinesterase play at the neuromuscular junction?

Acetylcholinesterase breaks down acetylcholine to prevent continuous muscle stimulation and ensure proper control of muscle contraction.

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How do neuromuscular junctions differ from cholinergic synapses?

  1. They are only excitatory, while cholinergic synapses may be excitatory or inhibitory
  2. They link neurones to muscles, while cholinergic synapses link neurones to other neurones or effector organs
  3. They only involve motor neurones, while cholinergic synapses involve sensory, relay, or motor neurones
  4. Acetylcholine binds to receptors on the muscle fibre membrane, while in cholinergic synapses it binds to receptors on postsynaptic neurone membrane

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