the cerebral cortex
TRANSCRIPT
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THE
CEREBRAL
CORTEX
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NEOCORTEX
Laminar pattern – 6 layers
10 – 20 billion neurons
95 % surface of the hemisphere
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B-Slide 4
Six Layers of Cortex
LGN input
Parvo
Magno
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NEOCORTEX,
types of neurons
Pyramidal neurons
Apical and basal
dendrites
Dendritic spines
Excitatory (glutamate)
Homogenous group
60 – 70 %
Non-pyramidal
neurons
Aspiny
Heterogenous group
Inhibitory (GABA)
30 – 40 %
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Electroencephalography (EEG) is an
electrophysiological monitoring method to record
electrical activity of the brain. It is typically
noninvasive, with the electrodes placed along the
scalp, although invasive electrodes are sometimes
used in specific applications.
The first human EEG recording obtained by Hans
Berger in 1924
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Brain Waves: State of the Brain
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, sleep disorders,
A flat EEG (no electrical activity) is clinical evidence of death
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B-Slide 9
Electroencephalogram (EEG)
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The EEG be recorded with Scalp electrodes through the
unopened skull or with electrodes on or in the brain.
A normal EEG
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Diagrammatic
comparison of the
electrical responses
of the axon and the
dendrites of a large
cortical neuron.
2. Mechanism of EEG
Current flow to
and from active
synaptic knobs on
the dendrites
produces wave
activity, while AP
are transmitted
along the axon.
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Measures brain activity
– Alpha waves = healthy resting adult
– Beta waves = concentrating adult
– Theta waves = normal children
– Delta waves = normal during sleep
Electroencephalogram (EEG)
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Electroencephalogram (EEG)
Measures synaptic
potentials produced at cell
bodies and dendrites.
– Create electrical currents.
Used clinically diagnose
epilepsy and brain death.
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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.
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Alpha Block: Replacement of the alpha rhythm by an asynchronous,
low-voltage beta rhythm when opening the eyes.
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•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.
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•Theta :more irregular than alpha waves
–Emitted from temporal and occipital lobes.
•Common in newborn some sleep in adult.
•Adult indicates severe motional stress.
–5-8 cycles/sec.
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•Delta: high-amplitude waves;
•Common during sleep and awake infant.
•In awake adult indicate brain damage.
–1-5 cycles/sec.
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I. Electroencephalogram (EEG)1. Brain Waves
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SPONTANEOUS
CORTICAL
ELECTRICAL
POTENTIALS:
THE EEG
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Mechanism of EEG
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
•EEG signals generated by cortex
•Currents in extracellular space generated by summation of EPSPs and IPSPs
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Frequency range: 40 Hz to 100 Hz (Highest)
Too much: Anxiety, high arousal, stress
Too little: ADHD (Attention deficit hyperactivity
disorder), depression, learning disabilities
Optimal: Binding senses, cognition, information
processing, learning, perception, REM sleep
Increase gamma waves: Meditation
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II Wakefulness and Sleep
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Sleep and Dreams:
Circadian Rhythms
Circadian Rhythms (biological changes
occurring on a 24-hour cycle)
– Our energy level, mood, learning, and
alertness all vary throughout the day.
– Sections of the hypothalamus called the
suprachiasmatic nucleus (SCN) and the
pineal gland regulate these changes.
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Sleep and Dreams:
Circadian Rhythms (Continued)
Disrupted circadian rhythms, through shift work, jet
lag, and sleep deprivation may cause mood
alterations, reduced concentration and motivation,
increased irritability, lapses in attention, and reduced
motor skills.
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Sleep and Dreams
What happens
to humans and
other animals
while we sleep
and dream?
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Sleep and EEG cont’d: Different stages of sleep and their respective brain waves:
– Stage 1: Low voltage random EEG activity (2-7 Hz)
– Stage 2: Irregular EEG pattern/negative-positive spikes (12- to 14- Hz)
– Also characterized with sleep spindle and K-complexes that could
occur every few seconds.
– Stage 3: Alternative fast activity, low/high voltage waves and high
amplitude delta waves or slow waves (2 Hz or less).
– Stage 4: Delta waves
– Stage REM (Rapid eye Movement): “episodic rapid eye movements,” low
v voltage activity.
– Stage NREM: All stage combined, but not including REM or stages that
may contain REM.
The K-complex occurs randomly in stage 2 and stage 3
– The K complex is like an awaken state of mind in that is associated with
a response to a stimulus that one would experience while awake.
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Sleep Stages
Cycle through 5 sleep stages every 90 minutes
Stage 1 Sleep
– brief stage; sensation of falling
Stage 2 Sleep
– 20 minutes; spindles (bursts of brain activity)
Stage 3 Sleep
– brief; transitioning to deeper sleep
Stage 4 Sleep
– 30 min.; delta (large, slow) brain waves; deep sleep
REM Sleep
– 10 minutes; vivid dreams
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Brain Waves and Sleep Stages
Sleep
– loss of
consciousness
that is:
periodic
natural
reversible
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EEG Sleep Patterns
There are two major types of sleep:
– Non-rapid eye movement (NREM)
– Rapid eye movement (REM)
REM (rapid eye movement): Dreams occur.
Low-amplitude, high-frequency oscillations.
Similar to wakefulness (beta waves).
Non-Rem (resting): High-amplitude, low-frequency waves (delta waves).
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Types of Sleep
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
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Non-REM Sleep Alpha, delta, theta activity are present in the EEG
record
– Stages 1 and 2: Alpha waves
– Stages 3 and 4: delta activity (synchronized)
Termed slow-wave sleep (SWS)
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?)
9.33
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REM Sleep Presence of beta activity (desynchronized EEG
pattern)
Physiological arousal threshold increases
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 9.36
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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.
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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
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Neural Regulation of Arousal Electrical stimulation of the brain stem induces arousal
– Dorsal path: RF--> to medial thalamus --> cortex
– Ventral path: RF --> to lateral hypothalamus, basal ganglia, and the forebrain
Neurotransmitters involved in arousal:
– NE neurons in rat locus coeruleus (LC) show high activity during wakefulness, low activity during sleep (zero during REM sleep)
LC neurons may play a role in vigilance
– Activation of ACh neurons produces behavioral activation and cortical desynchrony
ACh agonists increase arousal, ACh antagonists decrease arousal
– 5-HT: stimulation of the raphe nuclei induces arousal whereas 5-HT antagonists reduce cortical arousal
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Neural Control of SWS
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
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Neural Control of REM Sleep
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
Increased ACh increases REM sleep
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Sleep homeostasis: adenosine
ATP ADP AMP Adenosine
Dependent on glucose, glycogen, and O2
Brain glycogen falls with sleep deprivation
Adenosine concentration rises during wake and falls during sleep
Caffeine blocks adenosine receptors
Other somnogens: PGD2 (medial preoptic area), TNFa...
PGE2 (wakefulness)
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2nd Part
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Wake-promoting pathways
periaqueductal grey
(dopamine)
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Wake promoting pathways
Many wake-promoting projections arise from neurons in the upper brainstem.
Cholinergic neurons (aqua) provide the major input to the thalamus, whereas
monoaminergic and (presumably) glutamatergic neurons (dark green) provide direct
innervation of the hypothalamus. basal forebrain, and cerebral cortex. The orexin
neurons in the lateral hypothalamus (blue) reinforce activity in these brainstem
arousal pathways and also directly excite the cerebral cortex and BF.
parabrachial nucleus (PB, glutamate);
PC, precoeruleus area (glutamate)
DR, dorsal raphe nucleus (serotonintuberomammillary nucleus (histamine);
vPAG, ventral periaqueductal gray (dopamine)
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Sleep promoting pathways
The main sleep-promoting pathways (magenta in B) from the
ventrolateral (VLPO) and median (MnPO) preoptic nuclei inhibit
the components of the ascending arousal pathways in both the
hypothalamus and the brainstem (pathways that are inhibited are
shown as open circles and dashed lines).
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Mechanisms of REM sleep
See Saper lab Nature 2006
pedunculopontine
tegmental (Ach)
Laterodorsal
tegmental nuclei (Ach)Tuberomammillary
nucleus 5-HT NE
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Mechanisms of non-REM sleep
TMN=tubermammillary nucleus
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waking and sleeping Shift
The ascending arousal systems are also capable of inhibiting the VLPO (C). This mutually
inhibitory relationship of the arousal- and sleep-promoting pathways produces the conditions
for a “flip-flop” switch, which can generate rapid and complete transitions between waking and
sleeping states. Abbreviations: DR, dorsal raphe nucleus (serotonin); LC, locus coeruleus
(norepinephrine); LDT, laterodorsal tegmental nucleus (acetylcholine); PB, parabrachial
nucleus (glutamate); PC, precoeruleus area (glutamate); PPT, pedunculopontine tegmental
nucleus (acetylcholine); TMN, tuberomammillary nucleus (histamine); vPAG, ventral
periaqueductal gray (dopamine)
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VLPO lesions produce insomnia
Lu, et al, 2000
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The flip-flop and bistability
Saper, et al, 01
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What stabilizes wake and sleep?
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Orexin
Hypocretin
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Orexin activates arousal regions
REM-on
neurons( )
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Orexin may stabilize sleep/wake behavior
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Sleep and Dreams: Sleep Disorders
Two major categories:
1. Dys-somnias
(problems in amount, timing,
and quality of sleep. A dyssomnia is a disorder of getting to
sleep or staying asleep or of excessive sleepiness.)
2. Parasomnias
(abnormal disturbances during sleep including sleepwalking,
nightmares, sleep paralysis, REM sleep behavior disorder, and
sleep aggression )
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Sleep and Dreams:
Three Forms of Dyssomnias
Insomnia: persistent problems in falling asleep,
staying asleep, or awakening too early
Sleep apnea: repeated interruption of breathing
during sleep
Narcolepsy: sudden and irresistible onsets of
sleep during normal waking hours
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Stages of Sleep And Brain
Mechanisms
Sleep apnea is a sleep disorder characterized by the inability to breathe while sleeping for a prolonged period of time.
Consequences include sleepiness during the day, impaired attention, depression, and sometimes heart problems.
Cognitive impairment may result from loss of neurons due to insufficient oxygen levels.
Causes include, genetics, hormones, old age, and deterioration of the brain mechanisms that control breathing and obesity.
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Stages of Sleep And Brain
Mechanisms Narcolepsy is a sleep disorder characterized
by frequent periods of sleepiness.
Four main symptoms include:
– Gradual or sudden attack of sleepiness.
– Occasional cataplexy - muscle weakness triggered by strong emotions.
– Sleep paralysis- inability to move while asleep or waking up.
– Hypnagogic hallucinations- dreamlike experiences the person has difficulty distinguishing from reality.
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Amines (locus coeruleus, dorsal raphe,
tuber mammillary nucleus)
Acetylcholine (LDT/PPT, basal forebr.)
Orexin/Hypocretin
GABA (ventrolateral preoptic nucleus)
Wake Non-REM REM
O
O
O
O
O
Activity of state-regulatory nuclei
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Sleep disorders are clinically important
15% of adults have chronic insomnia
24% of adults have chronic sleepiness
25% of motor vehicle accidents with loss of consciousness are due to falling asleep
60% of fatal truck accidents are due to sleepiness
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Impaired orexin signaling and narcolepsy
Daytime sleepiness
Fragmented sleep
Cataplexy (lack of response to external stimuli and by muscular rigidity)
Sleep paralysis
Hypnagogic hallucinations
Loss of orexin neurons
HumansMice/Rats/Dogs
Lack of orexin
Loss of orexin neurons
Lack of orexin receptors
Narcolepsy
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Stages of Sleep And Brain
Mechanisms
The locus coeruleus is small structure
in the pons whose axons release
norepinephrine to arouse various areas
of the cortex and increase wakefulness.
Usually dormant while asleep.
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Structure Neurotransmitter(s) it
releases
Effects on Behavior
Pontomesencephalon Acetylcholine, glutamate Increases cortical arousal
Locus coeruleus Norepinephrine Increases information
storage during
wakefulness; suppresses
REM sleep
Basal forebrain
Excitatory cells Acetylcholine Excites thalamus and
cortex; increases
learning, attention;
shifts sleep from NREM
to REM
Inhibitory cells GABA Inhibits thalamus and
cortex
Hypothalamus
(posterior HT)
Histamine Increases arousal
Lateral Hypothalamus Orexin/hypocretins Maintains wakefulness
Dorsal raphe and pons Serotonin Interrupts REM sleep
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Epilepsy
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Epilepsy
A group of chronic CNS disorders characterized by recurrent seizures.
Seizures are sudden, transitory, and uncontrolled episodes of brain dysfunction resulting from abnormal discharge of neuronal cells with associated motor, sensory or behavioral changes.
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Epilepsy
There are 2.5 million Americans with epilepsy in the US alone.
More than 40 forms of epilepsy have been identified.
Therapy is symptomatic in that the majority of drugs prevent seizures, but neither effective prophylaxis or cure is available.
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Epilepsy
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Causes for Acute Seizures
Trauma
Encephalitis
Drugs
Birth trauma
Withdrawal from
depressants
Tumor
High fever
Hypoglycemia
Extreme acidosis
Extreme alkalosis
Hyponatremia
Hypocalcemia
Idiopathic
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I. Partial (focal) Seizures
A. Simple Partial Seizures
B. Complex Partial Seizures
II. Generalized Seizures
A. Generalized Tonic-Clonic Seizures
B. Absence Seizures
C. Tonic Seizures
D. Atonic Seizures
E. Clonic Seizures
F. Myoclonic Seizures
G. Infantile Spasms
Classification of Epileptic Seizures
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I. Partial (Focal) Seizures
A. Simple Partial Seizures
B. Complex Partial Seizures.
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A. Simple Partial Seizures (Jacksonian)
Involves one side of the brain at onset.
Focal w/motor, sensory or speech disturbances.
Confined to a single limb or muscle group.
No alteration of consciousness.
EEG: Excessive synchronized discharge by a small
group of neurons. Contralateral discharge.
I. Partial (Focal) Seizures
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B. Complex Partial Seizures (Temporal Lobe epilepsy or Psychomotor Seizures)
Produces confusion and inappropriate or dazed behavior.
Motor activity appears as non-reflex actions. Automatisms (repetitive coordinated movements).
Wide variety of clinical manifestations.
Consciousness is impaired or lost.
EEG: Bizarre generalized EEG activity with evidence of anterior temporal lobe focal abnormalities. Bilateral.
I. Partial (focal) Seizures
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II. Generalized Seizures
Generalized Tonic-Clonic Seizures
Absence Seizures
Tonic Seizures
Atonic Seizures
Clonic Seizures
Myoclonic Seizures.
Infantile Spasms
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II. Generalized Seizures
In Generalized seizures, both hemispheres are widely involved from the outset.
Manifestations of the seizure are determined by the cortical site at which the seizure arises.
Present in 40% of all epileptic Syndromes.
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II. Generalized Seizures
A. Generalized Tonic-Clonic Seizures Recruitment of neurons throughout the cerebrum
Major convulsions, usually with two phases:
1) Tonic phase
2) Clonic phase
Convulsions:
– motor manifestations
– may or may not be present during seizures
– excessive neuronal discharge
Convulsions appear in Simple Partial and Complex Partial Seizures if the focal neuronal discharge includes motor centers; they occur in all Generalized Tonic-Clonic Seizures regardless of the site of origin.
Atonic, Akinetic, and Absence Seizures are non-convulsive
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Neuronal Correlates of Paroxysmal
Discharges
Generalized Tonic-Clonic Seizures
II. Generalized Seizures
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II. Generalized Seizures
A. Generalized Tonic-Clonic Seizures
Tonic phase:
- Sustained powerful muscle contraction
(involving all body musculature) which arrests
ventilation.
EEG: Rhythmic high frequency, high voltage
discharges with cortical neurons undergoing
sustained depolarization, with protracted trains
of action potentials.
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II. Generalized Seizures
A. Generalized Tonic-Clonic Seizures
Clonic phase:
- Alternating contraction and relaxation, causing a reciprocating movement which could be bilaterally symmetrical or “running” movements.
EEG: Characterized by groups of spikes on the EEG and periodic neuronal depolarizations with clusters of action potentials.
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B. Absence Seizures (Petite Mal)
Brief and abrupt loss of consciousness, vacant stare.
Sometimes with no motor manifestations.
Minor muscular twitching restricted to eyelids (eyelid flutter) and face.
Typical 2.5 – 3.5 Hz spike-and-wave discharge.
Usually of short duration (5-10 sec), but may occur dozens of times a day.
No loss of postural control.
II. Generalized Seizures
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Neuronal Correlates of Paroxysmal
Discharges
Generalized Absence Seizures
II. Generalized Seizures
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B. Absence Seizures (con’t)
Often begin during childhood (daydreaming attitude, no participation, lack of concentration).
A low threshold Ca2+ current has been found to govern oscillatory responses in thalamic neurons (pacemaker) and it is probably involve in the generation of these types of seizures.
EEG: Bilaterally synchronous, high voltage 3-per-second spike-
and-wave discharge pattern.
Spike-wave phase:
Neurons generate short duration depolarization and a burst of action potentials, but there is no sustained depolarization or repetitive firing of action potentials.
II. Generalized Seizures
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Cellular and Synaptic Mechanisms of
Epileptic Seizures
(From Brody et al., 1997)
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Treatment of Seizures
Goals:
Block repetitive neuronal firing.
Block synchronization of neuronal
discharges.
Block propagation of seizure.
Minimize side effects with the simplest drug
regimen.
MONOTHERAPY IS RECOMMENDED IN MOST CASES
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Treatment of Seizures
Strategies:
Modification of ion conductances.
Increase inhibitory (GABAergic) transmission.
Decrease excitatory (glutamatergic) activity.
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Actions of Phenytoin on Na+
Channels
A. Resting State
B. Arrival of Action
Potential causes
depolarization and
channel opens allowing
sodium to flow in.
C. Refractory State,
Inactivation
Na+
Na+
Na+
Sustain channel in
this conformation
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Ca2+ Channels
Ca 2+
B
: sites of N-linked glycosylation.
P: cAMP-dependent protein kinase
phosphorylation sites
Ion Channels
• Voltage-gated
• Multiple Ca2+ mediated
events
• Missense mutations of the
T-type Ca-channel a1H
subunit is associated with
Childhood Absence
Epilepsy in Northern
China
Drugs Used:
• Calcium Channel
Blockers
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GABAergic SYNAPSE
Drugs that Act at the
GABAergic Synapse
GABA agonists
GABA antagonists
Barbiturates
Benzodiazepines
GABA uptake inhibitors
Goal : GABA Activity
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GLUTAMATERGIC SYNAPSE
Excitatory Synapse.
Permeable to Na+, Ca2+ and K+.
Magnesium ions block channel in resting state.
Glycine (GLY) binding enhances the ability of GLU or NMDA to open the channel.
Agonists: NMDA, AMPA, Kianate.
Goal: GLU Activity
Mg++
Na+
AGONISTS
GLU
Ca2+
K+
GLY