Sleep, wakefulness, epilepsy and EEG Flashcards
(26 cards)
Sleep is usually described in relation to consciousness
a) easily reversible state of inactivity with a b) lack of interaction with the environment.
Consciousness has been described as having three states (Antonio Damasio)
Wakefulness – animal is alert, detects objects and pays attention to them Core consciousness –wakefulness plus emotional responses, and simple
memory.
Extended consciousness – all of the above plus self awareness, autobiographical memory, language and creativity.
what are the theorised functions of sleep
- processing and storage of memories
- recuperation of the bodies immune system
- to conserve energy
There are two main forms of externally discernable sleep
1) when the eyes move rapidly from side to side (REM sleep) or
2) when they do not (non REM, slow wave or deep sleep) however there are other determinants
how can the neuronal activity during the different stages of wakefulness be measured
Electroencephalogram (EEG)
how does an EEG work
- Post synaptic activity of individual neurons not picked up
- Post synaptic activity of synchronised dendritic activity can be picked up.
- Synchronisation is either by neuronal interconnections or by pacemaker
- The more neurons that are synchronised, the bigger the peaks on the EEG.
Influence of the thalamus on brain waves during somnolence:
when the brain wants to be awake it actively inhibits sleep and vice versa:
- excitation arrives at the reticular formation and therefore this activates depolarisation which travels to the thalamus, this produces a nonrhythmic output which results in increased arousal (alpha and beta waves)
- when inhibition arrives at the reticular formation this produces hyperpolarisation which means the thalamus produces a rhythmic output which results in slow EEG waves in the cerebral cortex
Epilepsy definition
a continuing tendency to have recurrent, unprovoked seizures.
what are the three main Classe of seizure
- partial
- generalised
- unclassified
simple partial seizure
- consciousness is preserved with +ve or –ve symptoms. Symptoms are related to areas affected in brain
complex partial
this can cause an impairment on consciousness, they start all over the brain or start at a focal point and spread all over, this is most common in the temporal lobe
Stages of complex partial seizures.
- Often begin with aura (fear, anxiety, déjà vu, olfactory sensation) linked to location
- Unresponsiveness then
- automatisms (lip smacking, patting, swallowing etc) & unusual sounds (grunting)
- Occasionally autonomic responses (Tachycardia pupil dilation)
- Post ictal headache common, often confusion.
these can evolve into generalised seizures which involve the whole of the brain and which impair consciousness
generalised seizures
both hemispheres are widely involved from the onset and the manifestations of the seizure are determined by the cortical site at which the seizure arises
ALWAYS ALTERATION TO CONCIOUSNESS
Absence seizures (Petit mal)
two forms, most (typical) are: • sudden onset (no aura) and
• abrupt cessation
• brief duration (20 sec),
• attack may be associated with mild clonic jerking of the eyelids
Myoclonic seizures:
myoclonic jerking is seen in a wide variety of seizures but when this is the major seizure type, it is treated differently to some extent from partial leading to generalized – treating Juvenile myoclonic seizures with carbamazepine will make them worse
• Atonic seizures:
sudden loss of postural tone; most often in children but may be seen in adults – generally rare.
• Tonic-clonic seizures (grand mal):
major convulsions with rigidity (tonic) and jerking (clonic), this slows over 60-120 sec followed by stuporous state (post-ictal depression)
Major convulsions, usually with two phases:
- 1) Tonic phase: muscles will suddenly tense up, causing the person to fall to the ground if they are standing.
- 2) Clonic phase: muscles will start to contract and relax rapidly, causing convulsions
Convulsions:
− motor manifestations
− may or may not be present during seizures
− excessive neuronal discharge
Status Epilepticus
- More than 30 minutes of continuous seizure activity
- Two or more sequential seizures spanning this period without full recovery between seizures
- Medical emergency
Relevant features of epilepsy are
- +/- Aura/warning/fear/Deja vu from patient
- Abnormal movements (lip smacking, patting, stroking) reported by patient or witness
- After effects? – memory loss, confusion, headache for mins or hours
- interictal examination which is usually normal
Non- invasive tests to confirm an epilepsy diagnosis
- ECG: Primarily done to check for abnormal function as there is a correlation between epilepsy and some cardiac problems such as arrhythmias and atherosclerosis.
- EEG: Interictal EEG is used to detect interictal epileptiform activity (IEA) which is a series of characteristic waves and spike used to predict the type of epilepsy
- CT scan: not normally done unless there is suspicion of a brain tumour or MR scans are not available. Resolution is lower, but cortical shrinkage or scars can be identified
- MRI: Used to identify areas of scarring, reduced perfusion, dysplasia (malformation) or areas of cortex damaged during stroke.
Pre-disposition
scar tissue
developmental issues
Pyramidal cell damage
sub-optimal regulation of neuronal excitability
disease that can cause it
Tumours
