9. Reticular Formation

Question 1

What is the definition of arousal?

Answer 1

The emotional state associated with some kind of goal or avoidance of something noxious.

Question 2

What is the definition of consciousness?

Answer 2

Something to do with the ‘awareness’ of both external world and internal states.

Question 3

What is required for consciousness?

Answer 3

The cerebral cortex and reticular formation. Form a positive feedback loop.

Question 4

What is the reticular network?

Answer 4

A population of specialised interneurones in the brainstem, a large part of which are devoted to arousal - the reticular activating system.

Question 5

Inputs from where regulate the level of arousal at the reticular formation?

Answer 5

Inputs from the sensory system and cortex.

Question 6

Where does the reticular system have outputs to?

Answer 6

Thalamus (sensory gating).
Hypothalamus.
Basal forebrain nuclei.
Spinal cord (muscle tone).

Question 7

How do the neurones in the brain fire when deprived of sensory input?

Answer 7

Fire synchronously.

Question 8

What types of waves are seen on an EEG when:
Awake.
Eye closed.
Stage 1.
Stage 2/3.
Stage 4.
REM sleep.

Answer 8

Awake - beta waves.
Eyes closed - alpha waves.
Stage 1 - background alpha waves and some theta waves.
Stage 2/3 - background theta waves with intermittent sleep spindles and K complexes.
Stage 4 - delta waves.
REM sleep - looks like beta waves.

Question 9

What happens as a general pattern on an EEG as a person grows down through the 4 stages of sleep and why?

Answer 9

Decreasing frequency and increasing amplitude as neuronal populations in the cortex become synchronous.

Question 10

Describe the basic neural mechanism of sleep?

Answer 10

About deactivating the reticular activating system (and so the cortex), leading to decreased cortical activity. Inhibition is assisted by removal of sensory inputs. The thalamus is also inhibited.

Question 11

Where are the neurones found that initiate REM sleep?

Answer 11

Groups of neurons in the pons.

Question 12

Why is a person difficult to rouse in REM sleep, but EEG activity is similar to that seen during arousal?

Answer 12

There is strong inhibition of the thalamus in REM sleep.

Question 13

Why is muscle tone in most of the body lost during REM sleep?

Answer 13

Descending inhibition of lower motor neurones by glycinergic fibres arising from the reticular formation and running down the reticulospinal tracts.

Question 14

Give 2 autonomic effects seen in REM sleep?

Answer 14

Penile erection and loss of thermoregulation.

Question 15

Where is there damage in brain death, and what is seen on an EEG?

Answer 15

Widespread cortical and brainstem death.

Flat EEG.

Question 16

Where is there damage in a coma, what is seen on an EEG and what is seen clinically?

Answer 16

Widespread cortical and brainstem damage.
Various EEG patterns detectable, no sleep-wake cycle detectable to connections between reticular formation and cortex are abnormal.
Unarousable and unresponsive to psychologically meaningful stimuli.

Question 17

Where is there damage in a persistent vegetative state, what is seen on an EEG and what is seen clinically?

Answer 17

Widespread cortical damage.
Various disordered EEG patterns detectable. Sleep-wake pattern detectable.
Unarousable and unresponsive it psychologically meaningful stimuli but with some spontaneous eye opening. Can localise to stimuli via brainstem reflexes.

Question 18

Where is there damage in locked in syndrome, and what is seen clinically?

Answer 18

Caused by basilar/pontine artery occlusion (supply the pons).
Eye movements preserved, but all other somatic motor functions lost form the pons down.