Chapter 4 Study Guide
What is the Biological rhythms also called?
Natural variations in biological functions, hormonal activity, temperature, and sleep that typically cycle
every 24 to 25 hours.
Suprachiasmatic nucleus (SCN):
An area of the hypothalamus that is located above the optic chiasm.
What does the SCN do?
Exerts the main control over biological rhythms.
What is the SCN also referred to as? Why?
Abiological clock; because damage to this area disrupts daily cycles in sleep and other biological
The Science of Sleep and Dreaming
Natural, periodically occurring state of rest characterized by reduced activity, lessened responsiveness
to stimuli, and distinctive patterns of brain activity.
State of sleep characterized by rapid eye movements, and often associated with dreaming.
Stages of sleep during which rapid eye movements typically do not occur.
How frequently does dreaming occur during NREM sleep and REM sleep?
Dreaming occurs most often in REM sleep.
Measuring Stages of Sleep
Measures brain waves
Measures movements of the eye
Measures electrical activity in the muscles Characteristics of Waking and Sleep Cycles
What does the EEG reveal when we are awake and alert?
Low-amplitude, high-frequency waves
What do our brain waves show when we are relaxed and drowsy, just before falling asleep?
An alpha rhythm of higher amplitude and slower frequency.
Higher amplitude and slower frequency
What three things happen when we are relaxed and drowsy, just before falling asleep?
1. Breathing and temperature drops
2. Body temperature drops
3. Muscles relax
Stage 1 Sleep:
Light sleep that occurs just after dozing off, characterized by brain waves called theta waves.
Stage 2 Sleep:
Typically follows stage 1 sleep, characterized by brief bursts of brain activity called sleep spindles as
well as K-complex responses to stimuli such as noises.
Stage 3 Sleep:
Typically follows stage 2 sleep, characterized by an EEG tracing 20 to 50% of which consists of delta
waves- virtually no eye movements during stage 3 sleep.
Stage 4 Sleep:
Deepest level of sleep, characterized by an EEG tracing exceeding 50% delta waves and virtually no
The Sleep Cycle
How long does it take to reach stage 4 sleep after first dozing off?
Roughly 45 minutes
How long do we remain in stage 4? What happens after this period of time?
About 30-40 minutes; we gradually return to stage 3 and 2 to stage 1.
When does the first REM cycle occur?
When we reenter stage 1, about 90 minutes after falling asleep.
When do we move through successive cycles during the night?
Between the various phases of REM and NREM sleep. Changes in Sleep Patterns withAge
Sleep 16 hours per day with 50% spent in REM sleep.
Sleep about 8 hours with 20% s