Sleep Flashcards
Explain the significance of amplitude and frequency in EEG waves in terms of cortical activity
- Alpha waves: High frequency high amplitude and occurs when the person is in a relaxed awake state
- Beta waves: Even higher frequency, low amplitude, asynchronized waves that occur when the person is fully awake
- Theta waves: low frequency and varies in amplitude and occurs when the person is asleep, when an adult is stressed or frustrated, it is also common in children
- Delta waves: Low frequency, high amplitude waves that occur when the person is in deep sleep
Describe the different sleep states
• Stage 1: Theta waves (low frequency high amplitude), slow eye movements, S-sleep which is light and a person can be easily roused from
• Stage 2: frequency decreases but there are bursts of rapid waves called “sleep spindles”, eye movements stop
• Stage 3: Delta waves with short episodes of faster waves, “sleep spindle” activity declines, deep sleep
• Stage 4: Delta waves, deep sleep. These stages are when sleep walking/ talking occurs and it is very difficult to wake someone in this stage
• REM stage (paradoxical sleep): Raid eye movements, beta waves that look like someone is awake, this is when dreaming occurs
- 25% of sleep (in adults)
- Gets longer throughout the night
- There is a profound inhibition of all other skeletal muscles due to a inhibitory projections in the pons that connect to the spinal cord. This prevents the acting out of dreams
Describe the typical pattern of a night’s sleep in an adult
- One goes through all the stages (typically taking 90 minutes) and then repeat stages 2-REM
- Deep sleep gets shorter and shorter over the night
- REM sleep gets increasingly longer over the night
Describe the physiological characteristics of stage 4 s-stage sleep
- Delta waves
- Slow waves
- Increased amount of high voltage
- Cough reflex suppressed
- Reduced blood flow and metabolism
- Growth hormone secretion
- Burst of sympathetic nerve activity during NREM
Describe the physiological characteristics of D-stage (REM) sleep
• Desynchronised (low voltage, mixed-frequency)
• Ventilation becomes faster and more erratic
• Cough reflex supressed
• Blood flow and metabolism comparable to wakefulness in total
- Blow flow and metabolism is higher than wakefulness in some regions of the brain e.g. the limbic system and visual association areas
Outline the neural mechanisms involved in the sleep/wake cycle
• During wakefulness
- Excitatory neurons in the ascending reticular activating system (ARAS), part of the reticular formation, are released from the inhibition from the sleep centres in the reticular formation
- This results in excitatory pathways both in the CNS and PNS
- This furthers results in more excitatory neurons in the ascending reticular activating system (ARAS) to be released from inhibition
- Positive feedback from the CNS and PNS sustains wakefulness in individuals for many hours
- This cycle continues until the excitatory neurons get fatigued and excitatory signals fade
• During sleep/ falling asleep
- Inhibitory peptide signals from the sleep centres in the reticular formation likely take over and rapidly dominate the weakening excitatory neurons leading to a rapid progression into a sleep state
- The inhibitory signals get fatigued and the excitatory cells are reinvigorated
• Excitatory neurons include: orexin (hypocretin) which is produced by the hypothalamus and is one of the supporting excitatory neurons in the CNS
- Inhibitory neurons include: melanin, which is produced by the pineal gland in the hypothalamus and serotonin which is produced by serotonergic nuclei in the reticular formation in the pons
What is insomnia?
- Affects 33% of adults
- Do not treat with sleeping pills chronically
- Chronic, primary insomnia: this is idiopathic and is not caused by any identifiable psychological or physiological problems
- Temporary, secondary insomnia: this is caused as a response to pain, bereavement or other crises’ and is associated with depression and PTSD
What is narcolepsy?
- Fall straight into REM sleep
- It is thought to be caused by a disfunction of orexin (hypocretin) in the hypothalamus
What are nightmares?
- Happens during REM
- Strong visual component
- Happens towards the end of the night
- When you wake up you remember everything
What are night terrors?
- Common in children aged 3-8
- Child will thrash, scream and may sit/stand with their eyes open but are not properly awake and fail to recognise their parents
- It happens in delta (deep) sleep`
- Early on in the night
- Child will not remember in the morning
What is Somnambulism?
- Sleep walking
- Happens in non-REM (mainly stage 4)
- More common in children and young adults, probably due to the decline in stage 4 as people get older
What is reticular formation behaviour disorder?
- It is due to a lack of inhibition from the pons
- People who have this will act out their dreams
Define what is meant by circadian rhythms
- Circadian rhythm is how biological systems oscillates in ~24 hour cycle
- It is controlled by the suprachiasmatic nucleus of the hypothalamus
Describe the role of the suprachiasmatic nucleus (SCN) in circadian rhythmicity
- There are cells in the back of the retina (that aren’t rod and cones) that send signals to the SCN which tell it about whether it is daytime or night-time, which keeps our circadian rhythms at ~24 hours
- This isn’t the only mechanism that controls the circadian rhythm, however, as blind people still have a circadian rhythmicity
- We don’t know the entire mechanism of control of the circadian rhythm but we do know that if you don’t have a hypothalamus/ if there is damage then the circadian rhythm is disrupted
- The hypothalamus regulates the activity of the pineal gland (which secretes melatonin) and when light hits the retina the hypothalamus suppresses the pineal gland and less melatonin is secreted. When light stops hitting the retina then more melatonin is produced and so we feel really sleepy
