Download 2 eng stages of sleep

The different stages of
sleep
Electroencephalogram recordings have paved
the way for an in-depth study of sleep. Thanks
to this technique, it has been possible to show
that sleep evolves in a continuous way,
demonstrating in regular succession aspects
which are biolectrically different.
Fig. 1: Hans Berger. The first person to
record electric activity in the human brain,
in 1924.
The
electroencephalogra
m recorded during
sleep is
distinguished in
humans by stages,
called I, II, III and
IV, and
characterised by a
gradual increase in
the number of low
frequency, large
width waves
(synchronised
neuronal bioelectric
activity) which make
up the high
frequency, narrow
width waves
(desynchronised
neuronal bioelectric
activity) typical of
the waking state.
(Fig. 2a).
Fig. 2: a) The electroencephalogram shows the variations in time
(seconds) of the electric activity of neurons, expressed in μV (10-6
V), in the different parts of the brain. These variations generate
waves of different frequencies and widths during the different
stages of the waking-sleeping cycle. b) An analysis of the
electroencephalogram shows us how the stages of sleep alternate
in cycles (NREM sleep, stages I-IV; REM sleep, indicated by the
black rectangle) in the course of an entire night’s sleep
(hypnogram ).
(Credit: G. Tononi, C. Cirelli. Sonno. In "Fisiologia Medica". Edi.
Ermes, 2005.)
This period is called
non rapid eye
movement, or
(NREM ) sleep, or
"slow wave sleep",
to distinguish it from
the last (fifth) stage
of sleep which is
characterised by an
electroencephalogra
m with high
frequency, narrow
width waves and rapid eye movement, known as REM sleep or "paradoxal sleep" because of
the electroencephalogram activity similar to that of the waking state. (Fig. 2a). This stage
concludes the ultradianous cycle of sleep (NREM sleep + REM sleep), a cycle which normally
appears in succession four or five times in humans during night rest, with a recurrence of 90120 minutes (Fig. 2b).
** DA AGGIUNGERE: phrases on graph, Fig. 2