Download nervous system part 6 EEG, walkfulness and sleep

Section 6
Electroencephalogram (EEG), Wakefulness
and Sleep
I.
Electroencephalogram (EEG)
1. Brain Waves
Brain Waves: State of the Brain
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Normal brain function involves continuous electrical
activity
Patterns of neuronal electrical activity recorded are
called brain waves
Brain waves change with age, sensory stimuli, brain
disease, and the chemical state of the body
An electroencephalogram (EEG) records this activity
EEGs can be used to diagnose and localize brain lesions,
tumors, infarcts, infections, abscesses, and epileptic
lesions
A flat EEG (no electrical activity) is clinical evidence of
death
The EEG be recorded with Scalp electrodes through the
unopened skull or with electrodes on or in the brain.
A normal EEG
Electroencephalogram (EEG)

Measures synaptic
potentials
produced at cell
bodies and
dendrites.
– Create electrical
currents.

Used clinically
diagnose epilepsy
and brain death.
EEG Patterns

Alpha: low-amplitude,
slow, synchronous
waves indicating an
“idling” brain
– Recorded from
parietal and occipital
regions.
 Person is awake,
relaxed, with eyes
closed.
– 10-12
cycles/sec
– 50 ~100 V.
•Beta:high-amplitude
waves seen in deep
sleep and when
reticular activating
system is damped
–Strongest from
frontal lobes near
precentral gyrus.
•Produced by
visual stimuli and
mental activity.
•Evoked activity.
–13-25
cycles/sec.
Alpha Block: Replacement of the alpha rhythm by an asynchronous,
low-voltage beta rhythm when opening the eyes.
•Theta :more
irregular than alpha
waves
–Emitted from
temporal and
occipital lobes.
•Common in
newborn some
sleep in adult.
•Adult indicates
severe
emotional stress.
–5-8
cycles/sec.
•Delta: high-
amplitude waves;
•Common during
sleep and awake
infant.
•In awake adult
indicate brain
damage.
–1-5
cycles/sec.
SPONTANEOUS
CORTICAL
ELECTRICAL
POTENTIALS:
THE EEG
2. Mechanism of EEG
Diagrammatic
comparison of the
electrical responses
of the axon and the
dendrites of a large
cortical neuron.
Current flow to
and from active
synaptic knobs on
the dendrites
produces wave
activity, while AP
are transmitted
along the axon.
Mechanism of EEG
•EEG signals generated by cortex
•Currents in extracellular space
generated by summation of EPSPs
and IPSPs

Continuous graph of changing voltage fields at scalp
surface resulting from ongoing synaptic activity in
underlying cortex
 Inputs from subcortical structures
– Thalamus
– Brainstem reticular formation
3. EEG Records During Epileptic
Seizure
Epilepsy is characterized by
uncontrolled excessive activity of
either a part or all of the central
nervous system.
Grand mal epilepsy: characterized
by extreme neuronal discharges in
all areas of the brain, last from a
few seconds to 3 to 4 minutes.
Petit mal epilepsy: Characterized
by 3 to 30 seconds of
unconsciousness or diminished
consciousness during which the
person has several twitch-like
contractions of the muscle.
II Wakefulness and Sleep
Sleep

Sleep is a behavior and an altered state of consciousness
– Sleep is associated with an urge to lie down for several hours in
a quiet environment

Few movement occur during sleep (eye movements)
– The nature of consciousness is changed during sleep
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We experience some dreaming during sleep
We may recall very little of the mental activity that occurred during sleep
We spend about a third of our lives in sleep
– A basic issue is to understand the function of sleep
EEG Sleep Patterns

There are two major types of sleep:
– Non-rapid eye movement (NREM)
– Rapid eye movement (REM)
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REM (rapid eye movement):
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Dreams occur.
Low-amplitude, high-frequency oscillations.
Similar to wakefulness (beta waves).
Non-Rem (resting):
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High-amplitude, low-frequency waves (delta waves).
Types of Sleep
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One passes through four stages of NREM during
the first 30-45 minutes of sleep
 REM sleep occurs after the fourth NREM stage
has been achieved
Non-REM Sleep
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Alpha, delta, theta activity are present in the EEG
record
– Stages 1 and 2: Alpha waves
– Stages 3 and 4: delta activity (synchronized)
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Termed slow-wave sleep (SWS)
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Light, even respiration
 Muscle control is present (toss and turn)
 Dreaming (could but not vivid, rational)
– Difficult to rouse from stage 4 SWS (resting brain?)
9.19
Types and Stages
of Sleep: NREM
– Stage 1 – eyes are
closed and relaxation
begins; the EEG
shows alpha waves;
one can be easily
aroused
– Stage 2 – EEG pattern
is irregular with sleep
spindles (high-voltage
wave bursts); arousal
is more difficult
–Stage 3 – sleep
deepens; theta and
delta waves appear;
vital signs decline;
dreaming is common
–Stage 4 – EEG
pattern is dominated
by delta waves;
skeletal muscles are
relaxed; arousal is
difficult
REM Sleep

Presence of beta activity (desynchronized EEG pattern)
 Physiological arousal threshold increases
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Heart-rate quickens
Breathing more irregular and rapid
Brainwave activity resembles wakefulness
Genital arousal

Pontine-Geniculate-Occipital (PGO) waves?
 Loss of muscle tone (paralysis)
 Vivid, emotional dreams
 May be involved in memory consolidation
9.22
Pontine-geniculate-occipital (PGO) wave –
A synchronized burst of electrical activity that originates in
the pons and like a wave it activates the lateral geniculate
nucleus (first relay of visual information)
and then the occipital lobe, specifically in the visual cortex
(which receives and puts together the visual information that
comes from the lat. geniculate nucleus).
PGO waves appear seconds before and during REM sleep.
Sleep
Stage
Cycles
A typical sleep pattern alternates between REM and NREM
sleep
SWS precedes REM sleep
REM sleep lengthens over the night
Basic sleep cycle = 90 minutes
The suprachiasmatic and preoptic nuclei of the hypothalamus regulate
the sleep cycle
Importance of Sleep
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Sleep is necessary for survival
Sleep appears necessary for our nervous systems to work
properly.
During the SWS, growth hormone secretion increase and
important for the infants growth and physical restorative
process of adult
During REM, brain blood flow and protein synthesis
increase, and it is important for the mental development of
infants and long-term memory and mental restoration in
adults.
Daily sleep requirements decline with age
What Happens if We are
Deprived of Sleep?
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Lack of alertness
Fatigue
Memory problems
Irritability
Depression
Lack of motivation
Accidents
Fibro Myalgia
Tips for Getting a Good Night’s Sleep
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Avoid caffeine and alcohol after dinner
 Keep a routine
 Don’t nap during the day
 Don’t go to bed hungry or right after eating
 Exercise
 Stop smoking
Rules for Optimal Sleep
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Get an adequate amount of sleep every
night
 Establish a regular sleep schedule
 Get continuous sleep
 Make up for lost sleep
Chemical Control of Sleep/Waking
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Sleep is regulated: loss of SWS or REM sleep is made
up somewhat on following nights
– Does the body produce a sleep-promoting chemical during
wakefulness or a wakefulness-promoting chemical during
sleep?
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Unlikely that sleep is controlled by blood-borne
chemicals in the general circulation given:
– Siamese twins share the same circulatory system, but sleep
independently
– Bottle-nose dolphins: the two hemispheres sleep
independently
9.29
Neural Regulation of Arousal
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Electrical stimulation of the brain stem induces arousal
–
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Dorsal path: RF--> to medial thalamus --> cortex
Ventral path: RF --> to lateral hypothalamus, basal ganglia, and the
forebrain
Neurotransmitters involved in arousal:
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NE neurons in rat locus coeruleus (LC) show high activity during
wakefulness, low activity during sleep (zero during REM sleep)
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Activation of ACh neurons produces behavioral activation and
cortical desynchrony
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LC neurons may play a role in vigilance
ACh agonists increase arousal, ACh antagonists decrease arousal
5-HT: stimulation of the raphe nuclei induces arousal whereas 5HT antagonists reduce cortical arousal
9.30
Neural Control of SWS
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The ventrolateral preoptic area (VLPA) is important
for the control of sleep
– Lesions of the preoptic area produce total insomnia,
leading to death
– Electrical stimulation of the preoptic area induces signs
of drowsiness in cats
– VLPA neurons promote sleep
Neural Control of REM Sleep
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The pons is important for the control of REM sleep
– Pontine-Geniculate-Occipital (PGO) waves are the first
predictor of REM sleep
– ACh neurons in the peribrachial pons modulate REM sleep
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Increased ACh increases REM sleep
Peribrachial neurons fire at a high rate during REM sleep
Peribrachial lesions reduce REM sleep
– Pontine ACh neurons project to the thalamus (control of
cortical arousal), to the basal forebrain (arousal and
desynchrony), and to the tectum (rapid eye movements)
– Pontine cells project via magnocellular cells within medulla to
the spinal cord: release glycine to inhibit alpha-motoneurons
(induce REM motor paralysis or atonia)
9.32
NT Interactions: REM Sleep
9.33
REM Dreaming
“vivid
~3
and exciting”
per night
NREM Dreaming
“just
thinking”
Shorter,
Longer,
more detailed
Midst
Fantasy
world
Logical,
less active
of nowhere
realistic
Nightmares
Frightening dream
Occur
Last
episodes
in the REM stages
about 20 minutes
Can
be result of taking drugs that affect
neurotransmitter action or from drug withdrawal
Severe
cases can be treated with medication
–Diazepam (tranquilizer)