Wakefulness and Sleep

Review vocabulary and definitions regarding the biological rhythms, sleep stages, brain mechanisms, and sleep disorders discussed in the lecture.

Endogenous circannual rhythm

An internally generated seasonal cycle, such as birds preparing for migration before temporal or environmental shifts occur.

Endogenous circadian rhythm

An internal biological cycle lasting approximately one day that regulates cycles of activity and sleep.

Zeitgeber

A German term meaning time-giver, referring to stimuli like light, meals, or exercise that reset internal biological clocks.

Jet lag

A disruption of biological rhythms resulting from traveling across time zones, characterized by daytime sleepiness or nighttime insomnia.

Suprachiasmatic nucleus (SCN)

Located in the hypothalamus above the optic chiasm, this structure is the primary driver of rhythms for sleep and body temperature.

Retinohypothalamic path

A small branch of the optic nerve that transmits light information from the retina to the suprachiasmatic nucleus.

Melanopsin

A specialized photopigment found in certain retinal ganglion cells that allows them to respond directly to average light intensity.

PER and TIM

Proteins produced by the period and timeless genes that oscillate over a $24$-hour period to regulate sleepiness in species like Drosophila.

Pineal gland

An endocrine gland located posterior to the thalamus that secretes the hormone melatonin.

Melatonin

A hormone released largely at night that increases sleepiness in diurnal animals like humans.

Coma

An extended period of unconsciousness with low brain activity and no response to stimuli, typically caused by trauma, stroke, or disease.

Unresponsive wakefulness syndrome

A condition where an individual alternates between sleep and moderate arousal but shows no awareness of surroundings or purposeful behavior.

Minimally conscious state

A state characterized by brief periods of purposeful actions and limited speech comprehension.

Brain death

A condition defined by a complete lack of brain activity and the absence of response to any stimulus.

Polysomnograph

A tool used to measure sleep stages by combining electroencephalograph records with eye-movement tracking.

Alpha waves

Brain waves with a frequency of $8$ to $12\,Hz$ that are characteristic of a state of relaxation.

Stage 1 sleep

The initial phase of sleep dominated by irregular, jagged, low-voltage waves.

K-complex

A sharp brain wave associated with the temporary inhibition of neuronal firing during stage $2$ sleep.

Sleep spindle

A burst of $12$ to $14\,Hz$ waves lasting at least half a second, occurring during stage $2$ sleep and linked to memory consolidation.

Slow-wave sleep (SWS)

Stages of sleep characterized by highly synchronized neuronal activity and large-amplitude waves.

REM sleep

Also known as paradoxical sleep, this stage features rapid eye movements, high brain activity, and relaxed postural muscles.

Reticular formation

A structure extending from the medulla to the forebrain that contains neurons involved in regulating arousal.

Pontomesencephalon

A part of the reticular formation that contributes to cortical arousal by releasing acetylcholine, glutamate, or dopamine.

Locus coeruleus

A small structure in the pons that releases norepinephrine to increase attention and enhance the activity of active neurons.

Orexin (hypocretin)

A peptide neurotransmitter released by the hypothalamus that is essential for maintaining wakefulness and staying awake.

PGO waves

High-amplitude electrical potentials detected in the pons, then lateral geniculate, then occipital cortex at the start of REM sleep.

Sleep apnea

A disorder characterized by an impaired ability to breathe while sleeping, often resulting in gasping for breath and daytime sleepiness.

Narcolepsy

A condition marked by sudden periods of sleepiness during the day, linked to a deficiency in orexin.

Cataplexy

A symptom of narcolepsy involving sudden muscle weakness while the person remains awake, often triggered by strong emotions.

REM behavior disorder

A condition where individuals move vigorously and act out their dreams during REM sleep due to an absence of muscle inhibition.

Night terrors

Severe experiences of intense anxiety during NREM sleep from which a person awakens screaming.

Activation-synthesis hypothesis

A theory suggesting that dreams are the brain's attempt to make sense of spontaneous activity in the pons and cortex.

Neurocognitive model

A perspective that views dreaming as thinking that occurs under unusual conditions with limited sensory input and reduced prefrontal activity.