Nervous System: The Reticular Formation And Consciousnes

Question 1

What is the reticular formation?

Answer 1

A population of specialised interneurones in the brainstem.

• Inputs from the sensory system and cortex regulate arousal
• Outputs are widespread

Question 2

What part of the reticular formation is responsible for arousal?

Answer 2

The reticular activating system

Question 3

What tool is commonly used to assess consciousness in clinical practice?

Answer 3

The glasgow coma scale - score from 3 to 15

Question 4

What is an EEG?

Answer 4

A electroencephalogram
Electrodes are placed on the scalp which measure electrical activity of thousands of neurones - commonly used to aid the diagnosis of epilepsy
Has poor spatial resolution

Question 5

What is the neural mechanism of sleep?

Answer 5

The reticular activating system is deactivated (hence inhibiting cortex) and inhibiting the thalamus

There is a positive feedback loop between the RAS and cortex, which is inhibited during sleep by removing sensory input and therefore leading to decreased cortical activity

Question 6

Describe the waves of the sleep cycle

Answer 6

Awake: B waves which are fast and irregular
Closed eyes: a waves which are slower and synchronous
Stage 1 sleep: theca waves which are very slow
Stage 2 and 3 sleep: sleep spindles of high thalamic activity then K complex which are broad and high amplitude
Stage 4 sleep: broad deep wave (like the K complex) which is the cortex intrinsic rate
REM sleep: same as awake

Question 7

What is REM sleep?

Answer 7

Initiated by groups of neurones in the pons, hard to rouse due to strong thalamic inhibition.

Muscle tone is lost but eye movement and other cranial nerve functions are preserved.

Autonomic effects include penile erection and loss of thermoregulation

Question 8

What are the functions of sleep?

Answer 8

Thought to be:

• enigmatic
• consolidate memories
• clear extracellular debris eg amyloid

Question 9

Name some common sleep disorders

Answer 9

• Insomnia which is commonly caused by anxiety, very rarely a neurological cause
• Narcolepsy where there is spontaneous sleep
• Sleep apnoea caused by a fat neck compressing the airways

Question 10

What are some disorders of consciousness?

Answer 10

• brain death
• coma, EEG patterns detectable but unarousable and unresponsive, no sleep wake cycle
• positive vegetative state, similar to coma but sleep wake cycle is detectable. Spontaneous eye opening
• Locked in syndrome, can be caused by basilar/pontine artery occlusion. Eye movements preserved but no other movement due to destroyed corticospinal tracts