This document discusses the sleep-wake cycle and circadian rhythms, highlighting the role of the suprachiasmatic nucleus as the central biological clock. It details how external zeitgebers, particularly light, synchronize this cycle and provides average sleep durations across different age groups. Additionally, it describes the physiological importance of sleep for recovery and cognitive functions such as memory consolidation.

1. THE SLEEP – WAKE CYCLE
By
ARINDAM SAIN

2. Circadian Rhythms, Sleep–Wake Cycle
 The daily sleep–wake cycle and other circadian rhythms (diurnal
rhythms) are controlled by endogenous rhythm generators
 The central biological clock (oscillator) that times these processes is
located in the suprachiasmatic nucleus (SCN) of the hypothalamus
 The endogenous circadian rhythm occurs in cycles of roughly 24–
25 hours, but is unadulterated only when a person is completely
isolated from the outside influences
 External zeitgebers (entraining signals) synchronize the biological
clock to precise 24-hour cycles
 The main external zeitgeber for 24-hour synchronization of the
sleep–wake cycle is bright light (photic entrainment)

3.  Infants sleep longest (about 16
hours/day, 50% REM)
 10-year-olds sleep an average 10
hours (20% REM)
 Young adults sleep 7–8 hours a
day
 Adults over 50 sleep an average
6 hours (both 20 % REM)
 When a person is deprived of
REM sleep, the duration of the
next REM phase increases
 The first two to three sleep
cycles (core sleep) are essential.

5. Consciousness: Selective attention, abstract thinking, the ability to
verbalize experiences, the capacity to plan activities based on
experience, self-awareness and the concept of values are some of the
many characteristics of consciousness
Attention: Sensory stimuli arriving in the sensory memory are evaluated
and compared to the contents of the long-term memory within fractions
of a second
Sleep: is a state of physiologic recovery, regularly repeated at night. The
day/night rhythm is associated with an altered state of consciousness.

6. Brain Wave States and Their Correlated Frequency and Physiology.
•Ross et al., 2019

7. Hegerl et al., 2016

9. Thieme et al

10. • The functions of
sleep are
homeostasis
(replenishment of
energy reserves with
high parasympathetic
involvement) and
consolidation
(stabilization) of
acquired procedural
knowledge (spoken
language, motor
functions).

11. A model for the regulation of transitions to the awake state and sleep.
Neuroscience, vol. 8, March 2007, 171–181.

12. THANK YOU