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Sleep and Dreaming

Influences on sleep and sleep disorders

  • 3 things to know
  • Paper 2

Overview

Circadian and ultradian rhythms, the pineal gland, melatonin and light, zeitgebers, jet lag and shift work, and the symptoms and explanations of insomnia and narcolepsy.

What you need to know

Answer each one before you reveal it.

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Key term

How well does light explain the sleep–wake cycle?

Key term

What is a circadian rhythm?

Key term

What is an ultradian rhythm?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is a circadian rhythm?

    Model answer

    A circadian rhythm is a biological cycle that repeats about every 24 hours. The sleep–wake cycle is the best-known example.

  2. 2

    What is an ultradian rhythm?

    Model answer

    An ultradian rhythm is a biological cycle that repeats more than once in 24 hours. The sleep cycle of about 90 minutes is an example.

  3. 3

    What is the pineal gland's role in sleep?

    Model answer

    The pineal gland is a small gland in the brain that releases the hormone melatonin. The pineal gland releases more melatonin when it is dark.

  4. 4

    How does melatonin affect sleep?

    Model answer

    Melatonin makes a person feel drowsy and prepares the body for sleep. Melatonin levels rise in the evening and fall in the morning.

  5. 5

    How does light control the release of melatonin?

    Model answer

    Light detected by the eyes is signalled to the body clock, which tells the pineal gland to reduce melatonin. Darkness allows melatonin levels to rise.

  6. 6

    What is a zeitgeber?

    Model answer

    A zeitgeber is an external cue that resets the body clock. Light is the most important zeitgeber for the sleep–wake cycle.

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