Sleep Flashcards
Circadian Rhythm
The most obvious circadian rhythm is the sleep pattern. The circadian rhythms take place over a day. Many animals are nocturnal and are active during the dark periods of the day; humans and other primates are diurnal , as we are active during the day. Throughout these 24-hour cycles, body temperature, hormone levels and brain activity change.
Controlled by light.
Zeitgeber
Any environmental cue that alters the circadian cycle is referred to as a zeitgeber (time giver). Light is a powerful zeitgeber and in our modern world, the change in light is in part responsible for the jetlag experience when travelling east to west over several time zones.
What part of the brain is most involved with circadian rhythms?
As with many of the regulatory processes in which humans and other animals engage, the hypothalamus is the site receiving most attention. Lesions of the suprachiasmatic nucleus (SCN) of the hypothalamus disrupt normal circadian rhythms
Why shouldn’t you use phones before bed?
The SCN, referred to as the circadian pacemaker, is clearly important and must therefore receive information from the environment in order to synchronize circadian rhythms and make adjustments. An obvious place to look for input mechanisms is the visual system. Retinal ganglion cells are photosensitive and independent from the rods and cones (see Chapter 10). The retinal ganglion cells have been shown to project to the SCN and their activity matches that of the entrainment of the circadian cycle (Berson et al., 2002). These retinal ganglion cells contain melanopsin (Do et al., 2009) which is most sensitive to blue light (Gooley et al., 2010). Blue light is emitted from visual display screens (e.g. smartphones and computers) and adjusts the circadian rhythm, leading to sleep problems and other psychological deviations (Cajochen et al., 2011); hence the recommendation not to use such devices before bedtime.
Melatonin
The SCN also controls melatonin . Melatonin is a hormone synthesized from serotonin within the pineal gland and synthesis is reduced upon exposure to light in the rat (Wurtman et al., 1964). High levels of melatonin are associated with darkness and sleep (Vaughan et al., 1976) and it has therefore been Cerebellum Medulla considered as a potential agent for improving sleep (Waldhauser et al., 1990).
What is sleep?
Stenberg (2007) defi nes sleep as a ‘reversible, physiological state with reduced motility and reduced responsiveness to sensory stimuli’ (p.1187). The identification of a function of sleep is somewhat more difficult.
How can the brains activity be measured ?
The brain’s activity can be measured by an electroencephalogram (EEG).
The three psychophysiological parameters that assess sleep architecture are the EEG, EOG (electro-oculogram) and electromyogram (EMG), measuring electrical activity of brain, eye movements and muscle movements respectively (see Chapter 6).
NREM Sleep
Stage 1 is the initial entry into the sleep state and represents a transitional state. The EEG indicates that the brain activity has changed, producing a theta wave. After a short period, the person enters stage 2 sleep. The EEG recording during stage 2 is irregular: there is theta activity, with a burst of activity called sleep spindles . Also within stage 2 are K-complexes which are negative potentials. Stage 3 sleep is characterized by delta waves , and during stage 3 the number of spindles diminishes. The difference between stage 3 and stage 4 is not clear-cut, but appears to be related to the number of delta waves. In stage 3 there are less than 50% delta waves, whereas in stage 4 there are more than 50%. These stages are called slow-wave sleep (SWS).
REM Sleep
The brain activity is desynchronised, with some theta and beta activity. Electrodes attached to the muscles of the eye (EOG) indicate that the eyes are active. This is called REM sleep , and during this sleep phase the rest of the body is paralysed.
Brain activity when we are awake
When we are awake, there are two types of brain activity (or waves): alpha and beta . Alpha activity predominates during rest and inactivity, whereas beta activity is associated with being alert. The brain’s activity changes through the four stages of sleep.
Cycle or REM and NREM
During a night’s sleep, there is a cycle of nonREM and REM sleep. Each cycle lasts about 90 minutes, a third of which may be REM sleep
Three neural systems are thought to produce sleep, and these communicate with each other.
The Forebrain
*generates SWS
The Reticular Formation
*Stimulation of the reticular formation will wake a sleeping animal
The Pons
*The pons is the f ocus of REM sleep, and if various cuts are made to transect the brainstem, the action of the pons’s ability to trigger REM sleep can be seen.
Neurotransmitters and Sleep
Acetylcholine in the pons produces eye activity during REM sleep and PGO w aves (Baghdoyan et al., 1984; Kodama & Honda, 1996). ACh is involved in vigilance and activation in wakefulness
Serotonin and noradrenaline have both been implicated in the control of sleep.
Consciousness is governed by three factors.
Activation ( A ) – the level of energy required by the brain (high during waking hours). • Input-output gating ( I ) – the process that facilitates or inhibits access of sensory information to the brain, and motor signals from the brain to the musculature of the body. • Modulation ( M ) – the chemical modulation of the brain via various neurotransmitters (high levels when awake).
The Electroenchephalogram
The EEG:
Measurement of generalized cortical activity
Noninvasive, painless
Diagnose neurological conditions such as epilepsy, sleep disorders and used for research
Records very small electrical fields generated by synaptic currents in pyramidal cells
