The Brainstem, Arousal & Sleep

Question 1

Where is the reticular formation?

Answer 1

At the centre of the brain stem

Question 2

Functions of the reticular formation?

Answer 2

Sleep regulation
Motor control
Cardioresp control 
Autonomic functions 
Motivation and reward 
Controls the level of sensitivity the upper brain receives

Question 3

What is the reticular formation made up of?

Answer 3

Discrete nuclei embedded in the white matter

Question 4

What are the two classifications of the reticular system?

Answer 4

Ascending reticular activating system (ARAS) - increases levels of consciousness

Secondary inhibition centre - decreases activity of the brain, reducing the level of consciousness

Question 5

How does the ARAS act and what inhibits the ascending reticular activating system to allow sleep?

Answer 5

Filters incoming signals

Hypothalamic sleep centres

Question 6

What is the ascending reticular activating system formed by?

Answer 6

Projection of the reticular formation

Question 7

How does LSD work?

Answer 7

Acts on the ARAS to reduce the filtering of incoming signals to higher centres of the brain
Alcohol can also inhibit this region

Question 8

What inputs does the ARAS have?

Answer 8

Auditory
Nociceptive
Visual
Somatosensory
Visceral
Olfactory

Question 9

Where does the ARAS output to?

Answer 9

The motor system (fibres descend in the cord to alter sensitivity of motor nuclei in the ventral horn)

Autonomic centres

Thalamus

Cortex

All raise level of consciousness

Question 9

During consciousness and REM sleep, what is the ARAS doing?

Answer 9

Stimulating thalamo-cortical neurones
-stimulates cortex for consciousness

Stimulating inhibitory neurones to act on inhibitory inter-neurones, further stimulating the consciousness of the cortex

Question 10

During slow wave sleep, what is the ARAS doing?

Answer 10

Neurones from the ARAS are silent, meaning no thalamo-cortical neurones are firing and there is significantly reduced consciousness

Question 11

What type of neurotransmitter is between the ARAS and thalamus?

Answer 11

Acetylcholine

Question 12

What happens when either the ARAS of cerebral cortex don’t work and cannot communicate?

Answer 12

Locked-in syndrome - brainstem damage

Persistent vegetative state - damage to cortex

Brain death - no activity on EEGs

Question 13

What is a coma?

Answer 13

A state of unconsciousness from which the person cannot be aroused using pain, light or sound

Patient initiates no voluntary movement

Question 14

Causes of a coma?

Answer 14

Intoxication
Metabolic disturbances
-diabetes
-hypoxia
Neurological events
-stroke
-tumour
-trauma

Question 15

What are some pathological alterations in the level of neurotransmitters in the brain and what can they cause?

Answer 15

Too much dopamine - schizophrenia

Low serotonin - depression

Low ACh from destruction of secreting cells - Alzheimer’s

Question 16

What are EEGs?

Answer 16

Measure electrical activity (excitatory and inhibitory) of the neurones by placing 16-25 electrodes on the scalp

Question 17

What are the different waves seen in an EEG?

Answer 17

Alpha (high frequency) - seen when awake and eyes shut. There is constant feedback between the cortical and thalamic projections

Beta - seen when awake with eyes open (mainly from parietal and frontal lobes)

Theta - seen in children and strong emotion in adults (parietal and temporal lobes)

Delta (low frequency) - deep sleep and serious brain conditions

Question 18

What is sleep important for?

Answer 18

CNS resetting/clearance

Memory (converts short-term to long-term)

Homeostasis

Question 19

What controls sleep?

Answer 19

The reticular formation and hypothalamus

Question 20

What is active and inactive during non-REM sleep?

Answer 20

Body is active

Brain is inactive

Question 21

What physiological changes happen in non-REM sleep?

Answer 21

Decreased cerebral blood flow
Decreased oxygen consumption
Decreased body temperature
Decreased BP
Decreased resp rate
Decreased BMR

Question 22

What is active/inactive during REM sleep?

Answer 22

Active brain

Inactive body

Question 23

What is seen on an EEG during REM sleep?

Answer 23

Appears as if awake - same projections happening between reticular formation, thalamus and cortex

Question 24

What physiological changes happen in REM sleep?

Answer 24

Irregular heart and resp rates
Increased BMR
Descending inhibition of motor neurones
Penile erection

Question 25

Which neurones switch REM sleep on and off?

Answer 25

On: cholinergic and serotoninergic neurones

Off: noradrenergic

Question 26

What is the pattern of spread of EEG waves during REM sleep?

Answer 26

From the pons, to the thalamus, then the occipital lobe

Question 27

What is narcolepsy?

Answer 27

When individuals experience attacks of sleep where it does not normally occur

Can also cause sleep paralysis where the individual is awake at night, begins to hallucinate but is unable to move

Due to abnormal functioning of cholinergic neurones

Question 28

What is the difference between primary and secondary insomnia?

Answer 28

Primary - due to problem in sleep mechanism

Secondary - physiological or medical problem

Question 29

What is sleep apnoea?

Answer 29

Loss of tone in upper resp tract muscles
Causes closure of the airways, reducing arterial pO2
Leads to arousal from sleep or into the lighter stages of non-REM sleep to maintain breathing

Question 30

How is sleep apnoea treated?

Answer 30

Use a positive oxygen pressure machine during sleep to keep airways patent (CPAP machine)