Lecture notes from Imperial College London, Medical Biosciences BSc, 2nd year, Neuroscience (NEU) module.
Learn what epilepsy is and what steps forward have been made in the management of the condition.
Learning outcomes:
- Identify the major neurotransmitters in the human nervous system a...
Seizures & epilepsy
- dramatic & alarming but common medical disorder
Neurotransmitters and receptors
- neurotransmitters affect electrical properties of postsynaptic neurons by excitation/ inhibition
- neurotoxins: toxic substances acting on the nervous system
=> many block neuromuscular junction, causing paralysis (respiratory muscles => suffocation)
- main neurotransmitters
=> acetylcholine (cholinergic): act on
=> nicotinic receptors: ionotropic (= ion-channel)
=> muscarinic receptors: metabotropic (= G-protein associated)
=> amino acids
=> glutamate: main excitatory neurotransmitter CNS (~60% brain synapses)
=> NMDA, AMPA, kainate (ionotropic), mGluR (metabotropic) receptors
=> GABA: main inhibitory neurotransmitter CNS (~40% brain synapses)
=> GABAa (ionotropic), GABAb (metabotropic)
=> aspartate: excitatory
=> glycine: inhibitory
=> biogenic amines: adrenaline, noradrenaline, dopamine, serotonin, histamine
=> affect behaviour, movement, homeostatic mechanisms
=> psychoactive drugs regulate their actions
=> peptides: endorphines, substance P
=> regulate emotions, perception of pain, responses to stress
=> “unconventional”: nitric oxide, endocannobinoids
=> ATP often co-released with other neurotransmitters + neurotransmitter on purinergic receptors
- postsynaptic response also depends on type of receptor + modulators
, - seizure = ictus = transient alteration of behaviour due to an abnormal excessive and synchronous
neuronal activity in the cerebral cortex
- electroencephalography (EEG) = recording of electrical activity in the brain
=> detect sings of neurological dysfunction in epileptic patients febrile seizure
(young child)
- provoked seizures (brought by systemic/ environmental factor: flashing light, fever, alcohol...)
=> not epilepsy photosensitive seizure
- very common: 50-60m people worldwide (= 1% pop)
=> symptomatic epilepsy: anatomical/ pathological abnormalities (genetic) and/or clinical features
indicative of an underlying disease or condition (acquired: brain injury, infections, stroke, tumour)
=> idiopathic epilepsy: in 60-70% cases, cause is not known (probably genetic inheritance)
How is EEG used in epilepsy?
- EEG records abnormal electrical activity through electrodes attached to the scalp
=> each line = 1 electrode => activity of large groups of neurons active at the same time
=> measures postsynaptic potentials (not a.p.)
=> the greater amplitude of the signal, the more synchronous is the activity
- advantages: low cost/ fast & precise
- limitations: poor spatial precision/ limited to cortex region
Types of seizures
- originate primarily in cortex (frontal, parietal, occipital, temporal lobes: including hippocampus)
=> seizure may spread to other regions
- partial/ focal seizures = restricted area involved // generalised seizures = entire brain involved
- partial with secondary generalisation seizures: starts locally & later spreads to both hemispheres
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