NEURO: Sleep Flashcards
What is an EEG?
EEG stands for electroencephalogram.
EEG measures the combined activity of a large number (1000s) of similarly orientated neurons. It requires synchronous activity across the groups of cells.
An EEG reflects the summed postsynaptic activity of large cell ensembles.
How does an EEG pick up on different levels of neuronal excitation?
Amplitude of an EEG signal depends upon how synchronous the activity of the neurons is.
When a group of cells is excited the tiny signals sum to generate a large surface signal.
Timing is everything – the same amount of excitation can occur, but at irregular intervals, resulting in a small summed signal.
Describe EEG rhythms.
EEG rhythms correlate with states of behaviours. They are categorised by their frequency range.
High-frequency low-amplitude is associated with alertness and waking.
Low-frequency high-amplitude is associated with non-dreaming sleep or coma.
List the different EEG rhythm during different functional states of the brain.
AWAKE WITH MENTAL ACTIVITY: β 14-30 Hz
AWAKE AND RESTING: α 8-13 Hz
SLEEPING: θ 4-7 Hz
DEEP SLEEP: <3.5 δ Hz
How does the brain generate regular rhythms?
There are two ways in which it can do this:
VIA PACEMAKER CELLS: The pacemaker cells in the thalamus act as conductors. The thalamus has communication with nearly every brain structure, so cells can coordinate the electrical activity between the neurons.
MUTUAL EXCITATION/INHIBITION:
There can be mutual excitation and inhibition between the cells that produce these rhythms via the cortical network.
What is the function of these brain rhythms?
The answer is, we don’t really know. However, there are hypotheses going around:
The hypothesis for slow-frequency high-amplitude rhythms during sleep: the thalamus acts as a gate-keeper for information transmission.
During wakefulness, information is transmitted. During sleep, there are synchronous rhythms that block information transmission.
The hypothesis for fast-frequency low-amplitude rhythms during wakefulness: the brain is ‘attention grabbing’ to ‘bind together’ regions needed for task execution.
What is sleep?
It is ‘a readily reversible state of reduced responsiveness to, and interaction with, the environment ’.
What are some differences in behaviour during different functional states of the brain?
AWAKE:
- EEG: low-amplitude, high frequency
- Sensation: vivid, externally generated
- Thought: logical, progressive
- Movement: continuous, voluntary
- REM: often
NON-REM SLEEP:
- EEG: high-amplitude, low frequency
- Sensation: dull or absent
- Though: logical repetitive
- Movement: occasional, involuntary
- REM: rare
REM SLEEP:
- EEG: low-amplitude, high frequency
- Sensation: vivid, internally generated
- Thought: vivid, illogical, bizarre
- Movement: muscle paralysis, movement commanded by the brain but not carried out
- REM: often
Describe the sleep cycle.
The EEG stages can be sub-divided to
indicate depth of sleep (Stages 1-4).
Each night begins with a period of
non-REM sleep, and as night progresses, there is a shift from
non-REM to REM sleep.
Sleep stages are then cycled throughout the night, repeating ~90 minutes.
Why do we sleep?
We don’t really know.
Is it to:
REST: do we sleep to recover cognitive function?
ADAPTATION: do we sleep to protect ourselves: hide from predators; conserve energy?
Describe the difference in neural mechanisms when we are asleep and awake.
WAKEFULNESS:
There is increased brainstem activity coordinating movement and maintaining homeostasis.
The increased excitatory activity decreases synchronous activity.
FALLING ASLEEP:
There is decreased brainstem activity, which allows for the synchronous activity to come through.
We get thalamic driven θ and δ waves.
What are some sleep promoting factors?
- adenosine: adenosine receptor activation decreases HR, decreases respiratory rate and decreases muscle tone (decreased BP)
- nitric oxide (NO)?: decreases muscle tone (decreased BP); NO also stimulates adenosine release
- inflammatory factors?
- melatonin?
What is a zeitgeber?
It is a rhythmically occurring natural phenomenon which acts as a cue in the regulation of the body’s circadian rhythms.
Examples would be temperature, or noises such as traffic and people.
What is involved in circadian rhythms?
The suprachiasmatic nucleus (SCN) is a pair of small nuclei in the hypothalamus of the brain, above the optic chiasma, thought to be concerned with the regulation of physiological circadian rhythms.
When the eye senses light, the SCN inhibits the pineal gland, which produces melatonin.
