PSYC 355 Ch 14 - Biological Rhythms, Sleep, and Dreaming

What is a circadian rhythm?

Functions of a living organism that display a rhythm of about 24 hours.

What does it mean to be diurnal?

Active during the light/day

What does it mean to be nocturnal?

Active during the dark/night

What are examples of biological rhythms that are shorter than a day?

Feeding and hormone release

What are biological rhythms that are shorter than a day called?

Ultradian rhythms

What is entrainment?

The process by which biological rhythms synchronize with external environmental cues, such as light and temperature.

What is a phase shift?

Shift in activity in response to a synchronizing stimulus, such as light.

What is a free-running rhythm?

When an animal maintains its own biological cycle without external cues, following own body’s action or internal clock.

What do circadian rhythms entrain to?

Light-dark cycles using different pathways in different species.

What is the biological clock?

The suprachiasmatic nucleus (SCN)

In mammals, how dopes light go from the eye to the SCN?

Through the retinohypothalamic pathway which transmits signals from the retina directly to the suprachiasmatic nucleus, helping to regulate circadian rhythms.

What does the retinohypothalamic pathway consist of?

Retinal ganglion cells that project to the SCN, these cells contain melanopsin, a photopigment sensitive to light, especially blue light.

True/False - The retinal ganglion cells in the retinohypothalamic pathway are not connected to photoreceptors.

True

Lesions in what area disrupt circadian rhythms?

In the SCN

Where is the SCN located?

The hypothalamus

What do transplant studies show about the endogenous period and where it is generated?

Proves the endogenous period is generated in the SCN and that each cell has a biological clock, if there is a transplant, the rhythm will match the donor’s cycle.

What is sleep synchronized to?

External cues, such as light and dark

How long is humans free-running clock?

About 25 hours

What is melatonin?

A hormone released by the pineal gland which helps coordinate circadian rhythm, helps cells to regulate clocks.

When is melatonin released?

A little before normal bedtime.

What is an EEG?

An electroencephalogram, measures electrical activity in the brain (levels of arousal).

What is an EOG?

An electro-oculography, records eye movements.

What is an EMG?

An electromyography, records muscle activity (muslce tension)

What are EEG signals the result of?

Current flow around the apical dendrites from large numbers of pyramidal cell (layer 5) in the cortex

What does the EEG of an awake person look like?

This EEG contains many frequencies, known as beta activity or desynchronized EEG, there is lots of activity but it is not coordinated, relatively fast frequencies and low amplitudes.

What is stage 3 (NREM) of sleep?

This is called slow wave sleep, characterized by large amplitude, very slow delta waves, demonstrates widespread correlated activity across the brain, “deep sleep”

What is REM sleep?

Rapid-eye movement sleep, specific patterned movement of the eyes, EEG activity is the same as an awake person, but muscles are limp, brainstem regions are profoundly inhibiting motor neurons to prevent movement during dreams

How many cycles does a typical night of sleep have?

4-5 cycles

What percentage of sleep is REM?

20%

What is more prevalent in cycles earlier in the night?

Stage 3 slow wave sleep

What is more prevalent in later cycles of sleep?

REM sleep

What happens to stage 3 sleep through the night?

It is lost more through the night towards morning.

How long does the sleep cycle last?

90-110 minutes which reflects a basic ultradian rest-activity cycle

What is infant sleep characterized by?

Shorter sleep cycles, more REM sleep which may provide essential stimulation to the developing nervous system

When does a 24 hour rhythm become evident in infants?

Around 16 weeks

About how many hours do newborns sleep?

18 hours

What happens to sleep as people age?

Total time asleep changes and the number of awakenings increases.

What stage sees the most dramatic decline in time spent in during sleep?

Stage 3

How much time is spent is stage 3 sleep at age 60?

Only half as much time as at age 20, by age 90 stage 3 has disappeared.

During what stage does sleep walking and talking happen?

During stage 3, slow wave sleep

What do people with narcolepsy suffer?

Frequent sleep attacks and excessive daytime sleepiness, they enter REM immediately after falling asleep, may show cataplexy

What is a possible cause of narcolepsy?

A mutant gene for the hypocretin receptor that causes cell death of cells that use and secrete hypocretin.

Is narcolepsy autoimmune disorder?

Yes because the cells are dying

What do hypocretin receptors do?

Project to other sleep centers that normally control the transition between wakefulness, NREM, and REM