Human Body

Nerves and Senses

How does short-term memory differ from long-term memory?

Short-term memory, also called primary memory, refers to small bits of information that can be recalled immediately. The recalled information has no permanent importance, such as a name or telephone number that is only used once. Long-term memory is the process by which information that for some reason is interpreted as being important is remembered for a much longer periods. Short-term memories may be converted to long-term memories.

Why do people need sleep?

Scientists do not know exactly why people need sleep, but studies show that sleep is necessary for survival. Sleep appears to be necessary for the nervous system to work properly. While too little sleep one night may leave us feeling drowsy and unable to concentrate the next day, a prolonged period of too little sleep leads to impaired memory and physical performance. Hallucinations and mood swings may develop if sleep deprivation continues.

Is it true that people need less sleep as they age?

As a person ages, the time spent each day sleeping decreases. The following table shows how much sleep is generally needed at night, depending on age:

Age Sleep Time (hours)
1–15 days 16–22
6–23 months 13
Age Sleep Time (hours)
3–9 years 11
10–13 years 10
14–18 years 9
19–30 years 8
31–45 years 7.5
45–50 years 6
50 years 5.5


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