10.5 Reticular Activating System

Question 1

Where does the reticular formation lie?

Answer 1

From caudal medulla to rostral midbrain

Question 2

What are the 3 columns of nuclei?

Answer 2

In the median column – the raphe nuclei
In the medial column – magnocellular nuclei (because of larger size of the cells)
In the lateral column – parvocellular nuclei (because of smaller size of the cells)

Question 3

How much sleep do we need?

Answer 3

8 hours between 10:30 and 6:30 but this increases at birth and decreases with age

Question 4

What happens to the sleep requirement in juveniles

Answer 4

They need slightly more sleep (9-10) due to their hormonal status and their circadian rhythm is shifted to a later window (1am-10am)

Question 5

What are the stages of sleep?

Answer 5

Stage I: 4-8Hz (theta)
II: increasing 10-12 Hz (alpha)
III - IV: deep sleep - slow wave
REM: low, voltage high frequency

Question 6

What is the cycle of sleep?

Answer 6

Descent into sleep takes about 1 hour, once stage IV has been reached the systems starts to revert back into active REM state with first phase shortest, subsequent ones of longer duration
It is an ordered process and you cannot jump between stages of sleep

Question 7

How many phases do you have and when do you most often wake up?

Answer 7

Tend to have 4-5 REM phases waking up mostly from REM phase

Question 8

What occurs in REM phase?

Answer 8

Rapid eye movement, but little EMG activity, increased ANS activity (HR, erection)
Dreaming
‘active brain in an inactive body’

Question 9

When do sleep talking and walking usually occur?

Answer 9

In non REM sleep ‘inactive brain in an active body’

Question 10

What neuromodulatory system is active in REM sleep and what areas of the brain?

Answer 10

cholinergic system is activated

Limbic system becomes activated but prefrontal cortex and posterior cingulate become less active

Question 11

What NT is involved with arousal?

Answer 11

Histamine from tuberomamillary body in hypothalamus which will signal via H1-3 receptors

Question 12

What part of the hypothalamus is important in activating sleep?

Answer 12

Ventrolateral preoptic nucleus

Question 13

What system in the hypothalamus is active during waekefulness?

Answer 13

Orexinergic system

Question 14

What happens with VPLO and orexin during sleep?

Answer 14

When the VPLO is activated it will send inhibitory signals to the monoaminergic neurons and orexin neurons (shuts down histaminergic activation)

Question 15

What causes sleep spindles in an EEG and how does this differ from an awake state?

Answer 15

Thalamic reticular cells inhibit thalamocortical cells causing hyperpolarisation, this activates T-type Ca channels which generates Ca spike which feeds back onto reticular cells

In an awake state the RAS and neuromodulatory input depolarisation followed by regular firing

Question 16

What are the physiological changes in sleep?

Answer 16

Reduced response to somatic sensory stimuli - inhibition of DC nuclei via GABA from pontine RAS

Muscle relaxation caused by glycine release from interneurons activated by reticulo-spinal projections (except pharynx/larynx muscle and respiratory muscles)

Question 17

What are the sleep pormoting areas?

Answer 17

Dorsal reticular formation
Solitary tract nucleus
Ventrolateral preoptic nucleus
Basal forebrain

Question 18

What are the activating areas of the brain?

Answer 18

Medial reticular formation 
Locus coeruleus 
Raphe nucleus 
Tuberomammilary nucleus 
Forebrain

Question 19

How do benzodiazepines affect sleep?

Answer 19

Put you into Stage I straight away
Prolonged deep sleep
Shorter REM phases
Create lasting ‘hangover

Question 20

How does caffeine effect sleep?

Answer 20

Delays ascending into deep sleep with re-awakening

Shortened overall sleep, REM and deep sleep

Question 21

What is the mechanism of arousal?

Answer 21

Arises as a consequence of activation of all neuromodulatory systems
Switched on by hypothalamic interactions (His) via negative feedback to the VLPN

Question 22

In REM sleep what part of the brain is active and what isnt?

Answer 22

limbic system active, prefrontal cortex is not

Question 23

What is the role of histamine in sleep?

Answer 23

Histamine is released from the tuberomamillary nuclei of the hypothalamus which gets input from VPLO and Orexin

When released = awake, decreased in sleep (antihistamines make you drowsy)

Question 24

Stimulation of which nucleus would lead to sleep in a normal person?

Answer 24

Ventrolateral preoptic nucleus - when stimulated it will send inhibitory signals to the monoaminergic neurons and orexin neurons (shuts down histaminergic activation)