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Heart beat is accelerated by

1. Sympathetic nerves and noradrenaline
2. Cranial nerves and adrenaline
3. Cranial nerves and acetylcholine
4. Sympathetic nerves and acetylcholine

Correct answer: Sympathetic nerves and noradrenaline

Solution

Heart rate increases when sympathetic stimulation acts on the heart, mainly through noradrenaline released from sympathetic nerve endings. This speeds the SA node and strengthens cardiac activity.

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