(Ch. 14) Circadian Rhythms and Sleep

Ultradian Rhythms

Biological rhythm that happens more than once a day

• rest-activity cycle in humans is 90 min

Infradian Rhythms

Biological rhythm that happens less than once a day

• menstrual cycle

Endogenous Circannual Rhythms

Internal mechanisms that operate on an annual/yearly cycle

• bird migratory patterns

• animals storing food for winter

• hibernation

Endogenous Circadian Rhythms

internal mechanisms that operate on an approximately 1-day cycle

• all animals have this

• regulates frequency of eating, drinking, body temp, secretion of hormones, urination…

• independent

Free-Running Rhythm

A rhythm that occurs when no stimulus resets it

• not phase-locked with day length

Phase Shift

Shift of activity due to a shift in a synchronizing stimulus

• e.g. changing time zones during travel

Zeitgeber

Term used to describe any stimulus that entrains the circadian rhythm to the earth’s 24h light/dark cycle… light is the main one

• exercise, noise, meals, temperature

Superchiasmatic Nucleus (SCN)

Part of the hypothalamus and the main control center of the circadian rhythms

• located dorsal to the optic chiasm

• damage results in less consistent body rhythms that are no longer in sync to environmental patterns of light and dark

• sends info to hypothalamic nuclei (and indirectly to the pineal gland) to modulate body temperature and production of hormones

Proof that the SCN controls the endogenous rhythm

When lesioned:

• Activity pattern more erratic, but still works

• when in constant darkness, activity becomes completely random

• Transplanting of cells restores rhythmicity, though the duration can change

Retinohypothalamic Tract

A small branch of the optic nerve that travels directly from the retina to the SCN

• used to reset the SCN when light is present

Melanopsin

Special photopigments that respond directly to light and do not require any input from rods or cones

• retinohypothalamic tract comes from this

Period (Per)

A gene that allows cells to generate a circadian rhythm

• based on early work with drosophila

Clock and Cycle Proteins

Two proteins that bind together to form a dimer

• binds to DNA to enchance the transcription of thegenes for period and cryptochrome

Per and Cry Proteins

Two proteins that bind together that inhibit the activity of the clock/cycle dimer.

• slows transcription of the per and cry genes

  • eventually breaks down, releasing clock/cycle from inhibition, allowing the cycle to start again.

Pineal Gland

Endocrine gland located posterior to the thalamus

• regulated by the SCN

• secretes melatonin in the evening

Wake EEG pattern

this EEG pattern is characterized by low-amplitude, high-frequency waves

Sleep EEG Pattern

this EEG pattern is characterized by high-amplitude, low-frequency waves

Alpha waves

Brain waves present when one begins a state of relaxation

Stage 1 Sleep

Stage of sleep characterized by

• EEG dominated by irregular, jagged, low-voltage waves

• brain activity begins to decline

Stage 2 Sleep

Stage of sleep characterized by

• Sleep spindles

• K-complex

Sleep Spindles

12~14 Hz waves during a burst that last at least half a second

• characteristic of stage 2 sleep

K-complex

A sharp, high-amplitude negative wave followed by a smaller, slower positive wave

Slow Wave Sleep (SWS, Stage 3 and 4 sleep)

Stage of sleep characterized by

• EEG recording of slow, large-amplitude delta waves

• slowing of heart rate, breathing rate, and brain activity

• highly synchronized neuronal activity

• predominate early in the night

Rapid Eye Movement Sleep (REM, Paradoxical Sleep)

Stage of sleep characterized by

• irregular, low-voltage, and fast (like waking)

• postural muscles of the body are more relaxed than other stages

• predominant later in the night, increases as the night progresses

• associated with dreaming

Encephale Isole

animal with transection at level of medulla

• shows normal responsiveness and sleep-wake patterns

• isolated brain

• shows that systems controlling sleep are found in the brain

Cerveau Isole

animal with transection through the mesencephalon

• shows constant unresponsiveness and signs of continuous SWS

• isolated cerebrum

• shows that the forebrain system promotes SWS

• shows that brainstem system promotes wakefulness and REM sleep

Forebrain System

Role in sleep: Display SWS by itself

• releases GABA into the hypothalamus

• stimulation of the preoptic area makes animals sleepy

• lesions induce insomnia

• if isolated - constant SWS

Brainstem System

Role in sleep: Activated forebrain into wakefulness

• Contains reticular formation

• stimulation promotes wakefulness and alertness

• lesions produce constant sleep states

Pontine System

Role in sleep: triggers REM sleep

• Sends widespread projections to promote REM sleep

Hypothalamic System

Role in sleep: Affects other three brain systems to determine sleep/wake

• Sends axons to other three sleep centers and seems to coordinate them

• enforces patterns of sleep

• loss of neurotransmitter used here leads to disorganized sleep

Preoptic Area (POA)

Location in the forebrain system that produces sleepiness, whereas lesions produce insomnia

Reticular formation

In the brain stem system

• collection of cells throughout midbrain and brainstem

• many of these neurons project to a variety of structures in brain to promote wakefulness

Iocus Coerules

Major source of NE for entire forebrain

• has stimulatory effects on alertness

• in the brain stem system

Narcolepsy

person (or animal) has sudden, intense bouts of sleep during day

• 5-30 minutes of sleep

Cataplexy

Sudden loss of muscle tone without loss of consciousness

• likely due to aberrant activity in pontine/REM system

• can be caused by strong emotions sometimes

Four Functions Frequently Ascribed to Sleep

1. Energy Conservation

2. Niche Adaptation

3. Body Restoration

4. Memory Consolidation

Energy Conservation

Reduced body temp, slower respiration, slower heart rate → reduced metabolic activity

• only reduced for about 5-10%

Niche Adaptation

Sleep enforces adaptation to a particular ecological niche

• e.x. if the animal is better at gathering food during daylight, or may avoid predators at night, then selective pressure may have favored sleeping in the other part of day

Energy conservation + Niche Adaptation

conserving energy by sleeping is coupled with a time of day when an animal would NOT be good at getting food

Body restoration

Sleep helps rebuild/restore body materials and functions

• prolonged deprivation → weakened immune system

• Work at night vs day → Increased risk of cancer

Memory Consolidation

Recent years, evidence indicates that sleep promotes memory consolidation:

• SWS helps in the consolidation of declarative memories

• involvement of REM sleep in the consolidation of procedural memories