Sleep, EEG and Epilepsy Flashcards
How EEG works
Post synaptic activity of individual neurons not picked up
Post synaptic activity of synchronised dendritic activity can be picked up
Sychronisation is either by neuronal interconnections or by pacemaker
the more neurons that are synchronised the bigger the peaks on the EEG
Brainstem reticular formation
Diffuse collection of at least 100 networks of neuromodulatory neurones spanning all three divisions of brainstem
Has projections to thalamus, hypothalamus, some brainstem nuclei, cerebellum, spinal cord and cerebral cortex
Receives input from cerebra, visual and auditory systems, sensory spinal systems, cerebellum, certain brainstem nuclei
Sleep mechanisms rely on communication between RF and thalamus (being the main real station to and from the cortex)
Thalamic function
Inhibiting thalamus decreases sensory throughput and exciting it increases sensory throughput
Major relay between sensory systems and cerebral cortex
Neural control of non-REM sleep
Charcacterised by synchronised cortical slow waves caused by a hyper polarised thalamus and decreased activity in arousal centres of reticulum
Inherent rhythmicity of thalamic regions as they hyper polarise due to reduced ascending reticular formation input
Orexin
Orexinergic neurones are normally active during wakefulness situated in lateral hypothalamus
These neurons project to cerebra, the arousal nuclei and ventrolateral pre-optic uncles infant hypothalamus - however no orexin receptors so neurones enhance arousal nuclei and cause indirect inhibition via reciprocal inhibition pathways between arousal centres and VLPO
What reacts to light/dark in eye?
Receptors in retina containing melanopsin react to light and synapse directly onto SCN resetting the clock gene
Narcolepsy
Onset due to specific loss of orexin containing neurons in lateral hypothalamus
Thought to be an inherited auto immune condition linked to ch 6
Repeated daytime sleeping, limb weakness during emotional episodes, wakening accompanied by muscular paralysis, vivid dream recollection just prior to wakening
Tx with modafanil, amphetamines, methylphenidate, SSRI/TCA suppress REM sleep, venlafaxine may help limb weakness (cataplexy)
Epilepsy history and tests
Aura/warning Abnormal movements Colour position When? After effects?
ECG, EEG and MRI
What are seizure categories?
Partial - simple or complex partial - evolving to secondarily generalised
Generelaised - absence, myoclonic, clonic, tonic, tonic-clonic, atonic
Unclassified
Simple partial
Focal with minimal spread of abnormal discharge
Normal consciousness and awareness maintained
Complex partial
Local onset and then spreads
Impaired consciosuness
Clinical manifestations vary with site of origin and degree of spread - presence and nature of aura, automatisms, other motor activity
Temporal lobe epilepsy most common
Secondarily generalised seizures
Begins focally with/without neuro simps
Variable symmetry, intensity and duration of tonic (stiffening) and clonic (jerking) phases
1-2 mins
Postictal confusion and somnolence
Generalised seizures
Absence (petit mal) - sudden onset and abrupt cessation, brief duration, consciousness is altered, mild clonic jerking of eyelids or extremities
Myoclonic - myoclonic jerking seen in a wide variety of seizures but tx differently when major seizure type
Tonic sudden loss of postural tone
Tonic-clinic - major convulsions with rigidity
Status epilepticus
More than 30 min of continuous seizure activity
Two or more sequential seizures spanning this period without full recovery between seizures
med emergency
Targets for anti-epileptics?
Increase inhibitory NT system - GABA Decrease excitatory NT - glutamate Block inward Na and Ca currents Increase outward positive effect - K+ Many act via many different mechanisms
