The brain stem: Sleep, circadian rhythms and homeostasis
What Is sleep?
Altered state of consciousness
- Drowsy
- Unconscious (but alert)
- Unconscious (hard to wake)
- Hallucinating (dreaming)
A period of altered bodily processes
- Different body temperature
- Different activity of immune system
- Slower heart and respiratory rate
Sleep = is a state that the brain actively produces – characterised by a
moderate decrease in brain activity and decreased response to stimuli
Sleep differs from the following states – coma, vegetative state, minimally
conscious state and brain death
Brain death = no sign of brain activity and no response to any stimulus
Coma = extended period of unconsciousness characterised by low brain
activity that remains fairly steady – person shows little response to stimuli
Vegetative state = person alternates between periods of sleep and
moderate arousal but no awareness of surrounding
Minimally conscious state – one stage higher than the vegetative state
marked by occasional brief periods of purposeful action and limited speech
comprehension
Sleep stages = The EEG records gross electrical potentials in an area of the
brain through electrodes attached to scalp
EEG allows researchers to discover there are stages of sleep
EEG allows us to compare brain activity at different times during sleep
, The brain activity from the
top to bottom of this figure
reflects a change from small
bursts of activity which
suggests different activity
levels across the brain
(desynchronisation)
to a slow wave rhythm/
oscillation in which all or
most of the brain is involved
- therefore showing
synchronization across the
brain.
EEG frequency bands
- EEG waveforms are classified by their frequency, amplitude and location
- Frequency is measures in Hertz
- 1 Hz = one cycle per second
4 distinct stages
- Relaxation – dominated by alpha waves
- Stage 1 – mostly alpha and beta activity. The EEG is dominated by irregular jagged and low
voltage waves – brain activity begins to decline
- Stage 2 – sleep spindles (short bursts) – and k complexes (transition from awake to sleep)
- Stages 3 and 4 – referred to as slow wave sleep (SWS). Increasing amounts of slow large
amplitude wave. Highly synchronised neuronal activity. Slowing of heart rate, breathing rate
and brain activity
- REM sleep – Rapid eye movement – postural muscles are paralysed. REM is associated with
dreaming (Dement)
Stages – when someone fall asleep, they go through stages 1,2,3,4 in sequenced order
After one hour the person goes through the stages back through 4,3,4 and then REM
Stages 3 and 4 predominantly early in the night – length of SWS decreases as the night progresses.
REM occurs later in the night – length Increase as night progresses
What Is sleep?
Altered state of consciousness
- Drowsy
- Unconscious (but alert)
- Unconscious (hard to wake)
- Hallucinating (dreaming)
A period of altered bodily processes
- Different body temperature
- Different activity of immune system
- Slower heart and respiratory rate
Sleep = is a state that the brain actively produces – characterised by a
moderate decrease in brain activity and decreased response to stimuli
Sleep differs from the following states – coma, vegetative state, minimally
conscious state and brain death
Brain death = no sign of brain activity and no response to any stimulus
Coma = extended period of unconsciousness characterised by low brain
activity that remains fairly steady – person shows little response to stimuli
Vegetative state = person alternates between periods of sleep and
moderate arousal but no awareness of surrounding
Minimally conscious state – one stage higher than the vegetative state
marked by occasional brief periods of purposeful action and limited speech
comprehension
Sleep stages = The EEG records gross electrical potentials in an area of the
brain through electrodes attached to scalp
EEG allows researchers to discover there are stages of sleep
EEG allows us to compare brain activity at different times during sleep
, The brain activity from the
top to bottom of this figure
reflects a change from small
bursts of activity which
suggests different activity
levels across the brain
(desynchronisation)
to a slow wave rhythm/
oscillation in which all or
most of the brain is involved
- therefore showing
synchronization across the
brain.
EEG frequency bands
- EEG waveforms are classified by their frequency, amplitude and location
- Frequency is measures in Hertz
- 1 Hz = one cycle per second
4 distinct stages
- Relaxation – dominated by alpha waves
- Stage 1 – mostly alpha and beta activity. The EEG is dominated by irregular jagged and low
voltage waves – brain activity begins to decline
- Stage 2 – sleep spindles (short bursts) – and k complexes (transition from awake to sleep)
- Stages 3 and 4 – referred to as slow wave sleep (SWS). Increasing amounts of slow large
amplitude wave. Highly synchronised neuronal activity. Slowing of heart rate, breathing rate
and brain activity
- REM sleep – Rapid eye movement – postural muscles are paralysed. REM is associated with
dreaming (Dement)
Stages – when someone fall asleep, they go through stages 1,2,3,4 in sequenced order
After one hour the person goes through the stages back through 4,3,4 and then REM
Stages 3 and 4 predominantly early in the night – length of SWS decreases as the night progresses.
REM occurs later in the night – length Increase as night progresses
