Cortical Excitability and EEG Flashcards
Why is cortical excitation required for the cerebrum?
What are the 2 forms of stimulation>
Cortical excitation is required to keep cerebrum active.
No cortical excitation = coma.
2 forms:
Direct neuronal stimulation
Neurohormonal systems
What is the function of the reticular excitatory area?
Direct neuronal stimuatlion ascends brainstem and reticulates out to cortex through thalamo-cortical projections
Reticular excitatory area → Thalamus → Reticulation to cortex
Gigantocellular neurones - Excitatory - Acetylcholine
What are the two different types of signals sent out by the reticular excitatory area?
Upwards → thalamus
Downwards → antigravity muscles and spinal reflexes
How is the reticular excitatory area inhibited?
Inhibitory reticular area sites below the REA
When activated, inhibits REA
Describe the 2 excitatory and 1 inhibitory pathway of activation of cortex
Rapid transmission
- Gigantocellular neurones
- Acetylcholine
- Rapidly acting, rapidly broken down - milliseconds
PRogressive transmission
- Neurohormonal neurones
- Longer term excitation
Reticular inhibitory area (RIA)
- MEdulla
- Serotonergic projections - serotonin (5-HT)
Desribe the 4 systems of neurohormonal control (NTs)
Noradrenaline system
- Excitatory
- Active during wakefulness and non-REM sleep, inactive during REM sleep
- Locus coeruleus
Dopamine system
- Excitatory or inhibitory
- Innervate specific regions
- Substantia nigra
Serotonin system
- Inhibitory
- Induction of sleep, pain control, mood
- Raphe nuclei
Acetylcholine system
- Gigantocellular neurones
- Drives REM sleep
- Causes acutely awake nervous system
- REA
Chief excitatory and inhibitory NTs in CNS?
Glutamate - excitiatory
- Binds NMDA or AMPA receptor
GABA - inhibitory
- Binds GABAr
Describe the positive feedback of cortex acitvaiton
Cortex activation sends signals to REA to produce more cortex activation
- Positive feedback
What are the three functional brain imaging techniques?
- Electroencephalography (EEG)
- Positron EMission Tomograph (PET)
- Functional Magnetic Resonance Imaging (fMRI)
What is the best and worst test for determining spatial resolution (location)?
Best = PET
Worst = EEG
What is the best and worst for determinig temporal resolution (brain activity with time)?
Best = EEG
Worst = PET
How does an electroencephalogram work and what is it used for?
Current runs through cranium/scalp and electrodes sense changes in the detected current.
Useful in:
- Seizures/epilepsy
- Sleep disorders
How does positron emission tomography work?
Measures distribution of organic molecules - positron emitting isotopes (tracer) IV injection.
Shows areas of activation as different hues on the scan
Superimposed onto structural image
How does fMRI work?
Measures oxygenated blood in the brain
Neurons firing = increased metabolic rate = increased oxygenated flow.
Good for spatial resolution, bad for temporal resolution.
What are comas and seizures?
Coma = widespread cortical daamge, dysfunction of REA causing permanent sleep.
Seizure = episodes of excessive neuronal activity in the brain
