WAKEFULNESS AND SLEEP

There are 2 kinds of Endogenous Rhythms…

Endogenous Circannual Rhythm and Endogenous Circadian Rhythm

Endogenous Circadian Rhythm

An internal 24-hour wake-sleep rhythm
Also, for eating, drinking, urination, metabolism, etc

Endogenous Circannual Rhythm

An internal rhythm that prepares for seasonal changes.

Setting and Resetting the Biological Clock

Circadian rhythms, with a period close to 24 hours, require regular adjustment to stay synchronized with the external environment.

External factors such as light, exercise, temperature, meals, and social cues help reset circadian rhythms, preventing them from drifting away from the correct time

Zeitgebers (TSITE-gay-ber)

Time-giver

Serve as external cues or stimuli that reset circadian rhythms, ensuring they remain aligned with the 24-hour day-night cycle.

Role of Zeitgebers

Light is identified as the primary zeitgeber for land animals, playing a crucial role in regulating the sleep-wake cycle and other physiological processes.

Other factors like exercise, temperature, meals, and social cues acts as zeitgebers, albeit with varying degrees of influence compared to light.

ex. Light cues the body to wake up and initiates various physiological processes.

Challenges for Circadian Regulation

Individuals in environments with disrupted light-dark cycles e.g. astronauts or those in polar regions, face difficulties maintaining circadian rhythms.

Blind individuals may struggle to regulate their biological clocks without a primary zeitgeber of light.

Challenges for Circadian Regulation

Jet Lag, Shift Work, Morning People and Evening People

jet lag

Disruption of circadian rhythms due to crossing time zones

Most people find it easier to cross time zones going west than east. Phase delay and phase advance

Stress elevates blood levels of the adrenal hormone cortisol. Prolonged elevation of cortisol damage neurons in hippocampus

shift work

A system in which employee/s work different times of the day and night

shift workers

Often experience disruptions in their circadian rhythm due to irregular working hours.

They continue to feel groggy on the job, they sleep poorly during the day, and their body temperature continues to peak when they are sleeping in the day instead of while they are working at night.

Morning People & Evening People

Morning people, larks, naturally feel more alert and energetic in the morning and tend to wake up early.

Evening people, owls, feel more productive and awake later in the day.

Partly influenced by genetics, lifestyle, and environmental cues.

How does the body generate a circadian rhythm?

Brain develops its own rhythms. Circadian rhythm remains steady

Suprachiasmatic Nucleus

Acts as the main driver

Continuously produces a circadian rhythm of action potentials. Maintains a circadian rhythm during isolations.

Rhythms come from the SCN itself.

How light resets the SCN

Retinohypothalamic path

Resetting of biological clocks through synchronization with light Melanopsin respond directly to light, and accordingly to the pace of light

Special ganglion cells respond on short wavelength light

The Biochemistry of the Circadian Rhythm

Drosophila contains PER and TIM genes

Messenger RNA levels that produces PER and TIM begins at low concentration and will increase as time goes by

Automatic feedback Mutations on the gene that produces PER proteins leads to altered sleep schedule

Melatonin

• SCN balances the waking and sleeping cycle

• Pineal gland releases this

• Can be seen almost to all chemicals in animals

• Sleepiness are increased in humans and wakefulness are increased in nocturnal animals

• Regulates sleep and wakefulness

Sleep and Other Interruptions of Consciousness

sleep, coma, vegetative state, minimally conscious state, brain death

Sleep

state actively produced by the brain, characterized by decreased activity and response to stimuli

coma

an extended period of unconsciousness caused by head trauma, stroke, or disease, with low brain activity and minimal response to stimuli

Sleeping person

can be awakened by stimuli

Coma

cannot be easily aroused or awakened by stimuli

Vegetative State

Alternate between periods of sleep and moderate arousal

Show no awareness of surroundings or purposeful behavior, though they may exhibit autonomic responses to stimuli

Minimally Conscious State

Characterized by brief periods of purposeful actions and limited speech comprehension

Brain Death

No sign of brain activity and response to any stimulus

Physicians typically wait for 24 hours of no brain activity before pronouncing brain death, at which point it is considered ethical to remove life support.

Brain Mechanisms of Wakefulness, Arousal, and Sleep

Reticular formation

structure that extends from the medulla into the forebrain.

Pontomesencephalon

a part of the reticular formation that contributes to cortical arousal

Locus Coeruleus (“dark blue place”)

small structure in the pons, is usually inactive, especially during sleep, but it emits bursts of impulses in response to meaningful events, especially those that produce emotional arousal

Orexin or Hypocretin

Another pathway from the hypothalamus, mainly from the lateral and posterior nuclei of the hypothalamus, releases a peptide neurotransmitter

Basal Forebrain

Other pathways from the lateral hypothalamus regulate cells

Responsible for arousal and attention

Reticular formation, Pontomesencephalon, Locus Coeruleus (“dark blue place”), Orexin or Hypocretin, Basal Forebrain

Sleep & the Inhibition of Brain Activity

Sleep depends partly on decreased sensory input to the cerebral cortex

Somnambulism

fancier term for sleepwalking

Lucid Dreaming

Someone is dreaming but aware of being asleep and dreaming

The Stages of Sleep

Electroencephalograph (EEG)

instrument that records an average of the electrical potentials of the cells and fibers in the brain areas nearest to each electrode on the scalp

Polysomnograph

combination of EEG and eye-movement records during various stages of sleep

Non-Rapid Eye Movement (NREM)

has 5 stages, the fifth is REM

stage 1 nrem

• our brain waves slowdown from the alpha rhythm and enter a pattern of theta waves.

• hypnagogic state, a state in which we experience brief but vivid dream like images, this also accompanies the transition from alpha waves to theta waves.

• lightest stage of sleep

stage 2 nrem

occurrence of k-complex (sharp wave associated to temporary inhibition of neuronal firing) and sleep spindles (burst of 12 to 14 hertz of waves for at least half a second) arise.

the brain waves are in the state of medium amplitude consisting of a frequency of 4 to 7 cycles per

stage 3 nrem

delta waves consist of a frequency of 1 to 3 cycles per second.

stage 4 nrem

the deepest stage of sleep delta waves slows down to about 0.5 to 2 cycles per second

REM stage 5

known as paradoxical sleep

EEG patterns usually observe a suggested level of arousal which is similar during the state of wakefulness. people tend to generate relatively rapid, low-amplitude brain waves that are similar to stage 1 sleep.

paradoxical or rem sleep

In the 1950s, the French scientist Michel Jouvet was trying to test the learning abilities of cats after removal of the cerebral cortex. Then recorded the same phenomenon in normal, intact cats and named it paradoxical sleep because it is deep sleep in some ways and light in others.

Only after repeated careful measurements they did conclude that periods of rapid eye movements occur during sleep. They called these periods rapid eye movement (REM) sleep.

The stages other than REM are known as non-REM (NREM) sleep.

Functions of Sleep

Essential rest for muscles; recover and repair Metabolism decreases, conserving energy, and supporting bodily functions

Facilitates important cellular maintenance, particularly in neurons, which helps optimize brain function

Reorganizes synapses, aiding in learning, memory consolidation, and cognitive processing

Helping to solidify new information and experiences

Changes in brain activity

Increase in activity in pons (triggers onset of REM sleep), limbic system (for emotional responses), parietal and temporal cortex. Decrease in activity in primary visual cortex, motor cortex, and the dorsolateral prefrontal cortex.

Lack of sleep

impairs memory and cognitive function.

Memory solidifies and may even improve after learning if followed by sleep or a nap.

Studying before sleep enhances retention compared to studying in the morning.

REM sleep and slow-wave sleep contribute to memory strengthening and creative problem solving.

Brain activity patterns resemble those during learning but occur more rapidly.

Hippocampal activity during sleep correlates with subsequent improvement in performance. Promotes the formation of new dendritic branches and strengthens memories.

Facilitates long-term potentiation by weeding out less successful synaptic connections.

Weakening or removing less appropriate synapses during sleep emphasizes strengthened ones from wakefulness.

Biological Perspective on Dreaming

The activation-synthesis hypothesis and The neurocognitive hypothesis

The activation-synthesis hypothesis

dream represents the brain’s effort to make sense

dreams begin from the spontaneous activity in the pons brain interprets the body position

during REM sleep, the motor cortex are inactive and major postural muscles are virtually paralyzed

The neurocognitive hypothesis

dreams as a thinking that happens under unusual conditions.

dreams begin with spontaneous brain activity that can be that can be related to past memories

during sleep, the brain can only collect few information from our sense organs

primary motor cortex, motor neurons of the spinal cord, and prefrontal cortex activity are suppressed we tend to forget our dreams and to lose track upon its underlying events

sleep disorders

Encompass a range of conditions that affect the quality, timing, and duration of sleep, leading to daytime dysfunction and impaired well-being.

sleep disorders include…

1. insomnia

2. sleep apnea

3. narcolepsy

4. Periodic Limb Movement Disorder (PLMD)

5. REM Behavior Disorder (RBD)

6. night terrors

7. sleepwalking

Functions of REM Sleep

A person spends a fifth of their life in REM sleep

• Infants gets more REM. More sleep predicts higher REM Sleep.

REM is hypothesized to be important for strengthening memory.

• However, antidepressants that decrease REM sleep lead to no memory problems.

REM shakes the eyes to get sufficient oxygen to the cornea

• Corneas get oxygen from surrounding air which is closed off when sleeping.

• Fluids behind the eye supply energy but become stagnant when there is no motion.

• Occurs towards the end of sleep when the fluids are most stagnant.

• However, decrease in REM sleep does not damage the cornea.

Insomnia

Sleep Apnea

Condition that can lead to insomnia

Impaired ability to breathe while sleeping.

Breathless periods of a minute or so from which they awaken gasping for breath.

Results from several causes including: genetics hormones old-age deterioration of the brain mechanisms that regulating breathing obesity (especially middle-aged man)

Narcolepsy

Neurological disorder characterized by excessive daytime sleepiness and sudden episodes of falling asleep during the day

. Runs in families, but most cases emerge in people with no affected relatives.

The cause relates to the neurotransmitter orexin.

People with narcolepsy lack the hypothalamic cells that produce and release orexin → neuropeptide that regulates arousal wakefulness and appetite

Common treatment: stimulant drugs like methylphenidate (ritalin)

people with sleep apnea

Increased risk of stroke, heart problems, and other disorders.

Advised to lose weight and avoid alcohol and tranquilizers.

Common treatment: Mask that covers the nose and delivers air under enough pressure to keep breathing passages open

main symptoms of narcolepsy are…

1. Attacks of sleepiness during the day

2. Occasional cataplexy

   • Attack of muscle weakness while the person remains awake.

   • Often triggered by strong emotions, such as anger or great excitement

3. Sleep paralysis

   • Inability to move while falling asleep or waking up. People have experienced it once or twice, but people with narcolepsy experience it frequently.

4. Hypnagogic hallucinations

   • Dreamlike experiences that a person has trouble distinguishing from reality, often occurring at the onset of sleep

Periodic Limb Movement Disorder (PLMD)

Repetitive and involuntary movements of the legs or arms during sleep.

Disrupts sleep continuity and leads to daytime fatigue and restless sleep.

Distinct from restless leg syndrome, in which people often feel an urge to kick a leg even while awake.

Mostly middle-aged and older, the legs kick once every 20-30 seconds for minutes or hours, mostly during NREM sleep.

REM Behavior Disorder (RBD)

Individuals physically act out their dreams during REM sleep.

They frequently dream about defending themselves which results in kicking, punching, or shouting.

Inadequate inhibitory transmission may be responsible for REM behavior disorder.

Night Terrors

Experience of intense fear, anxiety, or dread during sleep, accompanied by sweating, screaming, and increased heart rate.

More severe than a nightmare, which is simply an unpleasant dream

Occurs during NREM sleep and are more common in children than adults.

Sleepwalking

Involves engaging in activities such as walking or eating while still asleep, typically during non-REM sleep stages.

Runs in the families and occurs mostly in children

More common when people are sleep deprived or under unusual stress

Usually harmless but not always Analogous condition: sleep sex or sexsomnia

• sleeping people engage in sexual behavior, either with a partner or by masturbation, and do not remember it afterward