Chapter 8: Stages of Sleep and Brain Mechanism

Question 1

alpha waves 272

Answer 1

1

Question 2

brain death 272

Answer 2

Brain death is a condition with no sign of brain activity
and no response to any stimulus. Physicians usually wait until someone has shown no sign of brain activity for 24 hours before pronouncing brain death, at which point most people believe it is ethical to remove life support.

Question 3

coma 272

Answer 3

1

Question 4

minimally conscious state 272

Answer 4

A minimally conscious state is one stage higher, with occasional, brief periods of purposeful actions and a limited amount of speech comprehension. A vegetative or minimally conscious state can last for months or years.

Question 5

polysomnograph 272

Answer 5

Polysomnograph, a combination of EEG and eye-movement records.

Question 6

vegetative state 272

Answer 6

Someone in a vegetative state alternates between periods of sleep and moderate arousal, although even during the more aroused state, the person shows no awareness of surroundings and no purposeful behavior. Breathing is more regular, and a painful stimulus produces at least the autonomic responses
of increased heart rate, breathing, and sweating.

Question 7

K-complex 273

Answer 7

A K-complex is a sharp wave associated with temporary inhibition of neuronal firing.

Question 8

paradoxical sleep 273

Answer 8

recorded slight movements of the muscles and EEGs from the hindbrain. During certain periods of apparent sleep, the cats’ brain activity was relatively high, but their neck muscles were completely relaxed.

Question 9

rapid eye movement (REM)

sleep 273

Answer 9

Periods of rapid eye movements occur during sleep. They called these periods rapid eye movement (REM) sleep, and soon realized that REM sleep was synonymous with what Jouvet called paradoxical sleep. Researchers use the term REM sleep when referring to humans but often prefer the term paradoxical sleep for nonhuman species that lack eye movements.

Question 10

sleep spindle 273

Answer 10

A sleep spindle consists of 12- to 14-Hz waves during a burst that lasts at least half a second. Sleep spindles result from oscillating interactions between cells in the thalamus and the cortex.

Question 11

slow-wave sleep (SWS) 273

Answer 11

Stages 3 and 4 differ only in the prevalence of these slow waves, and some authorities combine them as a single stage, slow-wave sleep (SWS).

Question 12

non-REM (NREM) sleep 274

Answer 12

The EEG record is similar to that for stage 1 sleep, but notice the difference in eye movements. The stages other than REM are known as non- REM (NREM) sleep.

Question 13

locus coeruleus 275

Answer 13

a 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. Axons from the locus coeruleus release norepinephrine widely throughout the cortex, so this tiny area has a huge influence.

Question 14

orexin (or hypocretin) 275

Answer 14

Another pathway from the hypothalamus, mainly from
the lateral and posterior nuclei of the hypothalamus, releases a peptide neurotransmitter called either orexin or hypocretin. The axons releasing orexin extend
from the hypothalamus to the basal forebrain and many other areas, enhancing wakefulness. Orexin is not necessary for waking up, but it is for staying awake. Drugs that block orexin receptors help people go to sleep, with possibly fewer side effects, compared to other drugs marketed for insomnia.

Question 15

pontomesencephalon 275

Answer 15

Reticular formation that contributes to cortical arousal is known as the pontomesencephalon These neurons receive input from many sensory systems and generate spontaneous activity of their own.

Question 16

reticular formation 275

Answer 16

A cut through the midbrain decreases arousal by damaging the reticular formation, a structure that extends from the medulla into the forebrain. Those with ascending axons are well suited to regulate arousal.

Question 17

basal forebrain 275

Answer 17

Other pathways from the lateral hypothalamus regulate
cells in the basal forebrain (an area just anterior and dorsal to the hypothalamus). Basal forebrain cells provide axons that extend throughout the thalamus and cerebral cortex. Some of these axons release acetylcholine, which is excitatory and tends to increase arousal. Acetylcholine is released during
wakefulness and REM sleep, but not during slow-wave sleep. During wakefulness, its release sharpens attention—that is, it increases the accurate, reliable detection of sensory stimuli.

Question 18

PGO waves 278

Answer 18

REM sleep is associated with a distinctive pattern of high-amplitude electrical potentials known as PGO waves, for ponsgeniculate- occipital. Waves of neural activity are detected first in the pons, shortly afterward in the lateral geniculate nucleus of the thalamus, and then in the occipital cortex

Question 19

insomnia 279

Answer 19

The best gauge of insomnia—inadequate sleep—is how someone feels the following day. If you feel tired during the day, you are not sleeping enough at night. Causes of insomnia include noise, uncomfortable temperatures, stress, pain, diet, and medications. Insomnia can also be the result of epilepsy, Parkinson’s disease, brain
tumors, depression, anxiety, or other neurological or psychiatric conditions.

Question 20

sleep apnea 279

Answer 20

One type of insomnia is sleep apnea, impaired ability to
breathe while sleeping. People with sleep apnea have breathless periods of a minute or so from which they awaken gasping for breath. They may not remember all their awakenings, although they certainly notice the consequences— sleepiness during the day, impaired attention, depression, and sometimes heart problems. People with sleep apnea have multiple brain areas that appear to have lost neurons, and consequently, they show deficiencies of learning, reasoning, attention, and impulse control.

Question 21

narcolepsy 280

Answer 21

Narcolepsy, a condition characterized by frequent periods of sleepiness during the day, strikes about 1 person in 1,000. Narcolepsy has four main symptoms,
although not every patient has all four. Each of these
symptoms can be interpreted as an intrusion of a REM-likestate into wakefulness:
1. Attacks of sleepiness during the day.
2. Occasional cataplexy—an attack of muscle weakness while the person remains awake. Cataplexy is often triggered by strong emotions, such as anger or great excitement.
3. Sleep paralysis—an inability to move while falling
asleep or waking up. Many people have experienced
sleep paralysis at least once or twice, but people with
narcolepsy experience it frequently.
4. Hypnagogic hallucinations—dreamlike experiences that the person has trouble distinguishing from reality, often occurring at the onset of sleep.
The cause relates to the neurotransmitter orexin. People with narcolepsy lack the hypothalamic cells that produce and release orexin. The most common treatment is stimulant drugs such as methylphenidate (Ritalin), which enhance dopamine and norepinephrine activity.

Question 22

periodic limb movement

disorder 280

Answer 22

Another sleep disorder is periodic limb movement disorder, characterized by repeated involuntary movement of the legs and sometimes the arms during sleep. In people with periodic limb movement disorder, mostly middle-aged and older, the legs kick once every 20 to 30 seconds for minutes or hours, mostly during NREM sleep.

Question 23

night terrors 281

Answer 23

Night terrors are experiences of intense anxiety from which a person awakens screaming in terror. A night terror is more severe than a nightmare, which is simply an unpleasant dream. Night terrors occur during NREM sleep and are more common in children than adults.The causes of sleepwalking are not well understood, but it is more common when people are sleep deprived or under unusual stress. It is most common during slow-wave sleep early in the night and usually not accompanied by dreaming.

Question 24

REM behavior disorder 281

Answer 24

For most people, the major postural muscles are relaxed and inactive during REM sleep. However, people with REM behavior disorder move around vigorously during their REM periods, apparently acting out their dreams. the results suggest that inadequate
inhibitory transmission may be responsible for REM
behavior disorder.

Question 25

REM

Answer 25

During paradoxical or REM sleep, the EEG shows irregular, low-voltage fast waves that indicate increased neuronal activity. In this regard, REM sleep is light. However, the postural muscles of the body, including those that support the head, are more relaxed during REM than in other stages. In this regard, REM is deep sleep. REM is also associated with erections in males
and vaginal moistening in females. Heart rate, blood pressure, and breathing rate are more variable in REM than in stages 2 through 4. In short, REM sleep combines deep sleep, light sleep, and features that are difficult to classify as deep or light. Consequently, we should avoid the terms deep and light sleep. In short, REM and dreams are not the same thing. During REM sleep, activity increased in the pons (which triggers the onset of REM sleep) and the limbic system (which is important for emotional responses). Activity decreased in the primary visual cortex, the motor cortex, and the dorsolateral prefrontal cortex but increased in parts of the parietal and temporal cortex. REM sleep apparently depends on a relationship between the neurotransmitters serotonin and acetylcholine.
Injections of the drug carbachol, which stimulates acetylcholine synapses, quickly move a sleeper into REM sleep. Note that acetylcholine is important for both wakefulness and REM sleep, states of brain arousal. Serotonin and norepinephrine interrupt REM sleep.