Global brain activity Flashcards
EEG
- Function
- Where it is used
Electroencephalogram
- Measures electrical rhythm in from the brain through electrodes placed on the scalp.
Use:
- Sleep studies
- Diagnosing + monitoring epilepsy
Mechanism of EEG
Measures voltage in the small fields generated by pyramidal cells.
Requirements for signal:
- Neurones must be active and synchronised
- Neurones must be parallel so that they summate.
Alpha rhythm
8-13 Hz
- Low amplitude
Indicates being awake but with eyes closed.
Beta rhythm
14-60 Hz
- Higher amplitude, high frequency.
Indicates being awake with eyes open
- Mental activity and attention is happening
Rhythm in REM sleep
Theta rhythm
4-7 Hz
- High amplitude, very low frequency.
Indicates drowsiness/ sleep
Delta rhythm
< 4 Hz
- Very low frequency and high amplitude
- Indicates deep sleep [stage 3 NREM]
Stages of sleep
Awake [alpha or beta rhythm]
Non REM {NREM]
- Stage 1: Theta waves
- Stage 2: Spindle waves + K complex
- Stage 3: Delta waves
REM: beta + alpha waves, desynchronised. Similar to being awake.
Thalamus in generating synchronous brain rhythms
Thalamic pacemaker neurones generate discharge patterns [voltage gated channels]
- Synchronises other thalamic neurones by setting a pace
Cells also become synchronised without pacemaker activity
- Each neurone is set at a frequency to fire, which lines up eventually.
Sleep cycle
Awake—> Stage 1 NREM—> 2—> 3—> 4—> 3—>2—> REM
Repeats
Behavioural criteria for sleep
Reduced motor activity
Decreased response to stimulation
Relatively easy to reverse
Stereotypical posture.
Possible functions of sleep
Conservation of energy
Thermoregulation
Neural maturation
Mental health
Cognition
Structural imaging of the brain
Static map of the brain
- Spatial configuration of tissue types.
Examples:
- MRI
- CT
Functional imaging of the brain
Dynamic map of the brain
- Indirectly measures neuronal activity.
Examples:
- PET
- fMRI
CT and imaging the brain
Used to diagnose:
- Tumours
- Bleeds
- Gross brain anomalies
MRI and brain imaging
Used to diagnose:
- Tumours
- Bleeds
- Brain anomalies
Better contrast resolution than CT:
- Better white-grey discrimination.
- Less radiation