Sleep stages and the sleep cycle

Overview

The functions of sleep and restoration theory, stages 1 to 4 and REM sleep, what happens to the body during REM, and how the sleep cycle changes across the night.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What are the main functions of sleep?

   Model answer

   Sleep allows the body to repair tissue and restore energy. Sleep also helps the brain process and consolidate memories.

2. 2

   How does restoration theory explain why we sleep?

   Model answer

   Restoration theory says sleep lets the body and brain recover from the day's activity. Deep sleep is linked to body repair, and REM sleep to brain recovery.

3. 3

   What are the effects of going without enough sleep?

   Model answer

   Lack of sleep causes tiredness, irritability and poor concentration. Long-term sleep loss is linked to weaker immunity and poorer memory.

4. 4

   What is the difference between REM and non-REM sleep?

   Model answer

   REM sleep involves rapid eye movements, an active brain and vivid dreaming. Non-REM sleep covers stages 1 to 4, when brain activity slows down.

5. 5

   Describe stage 1 of sleep.

   Model answer

   Stage 1 is a light sleep between waking and sleeping. A person in stage 1 is easily woken, and brain waves slow to theta waves.

6. 6

   Describe stage 2 of sleep.

   Model answer

   Stage 2 is a slightly deeper sleep in which heart rate and body temperature fall. Brain activity shows short bursts called sleep spindles.

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