8. Reticular formation & control of consciousness Flashcards Preview

ESA 4- Nervous system > 8. Reticular formation & control of consciousness > Flashcards

Flashcards in 8. Reticular formation & control of consciousness Deck (11):
1

What is consciousness and which brain structures does it require?

"Awareness" of both external world and internal states.

Requires +ve feedback loop between CEREBRAL CORTEX and RETICULAR FORMATION.

2

What is arousal?

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

3

What is the reticular formation? Describe its inputs and outputs.

Reticular formation = population of specialised interneurones in the brainstem involved in consciousness and arousal.

Inputs from:
- sensory system (e.g. can't sleep when light/noisy)
- cortex (e.g. can't sleep when anxious)

Outputs to:
- thalamus (sensory gating)
- hypothalamus
- basal forebrain nuclei
- spinal cord (muscle tone)

4

What is the reticular activating system?

Part of the reticular formation devoted to arousal, including stimulation of the cortex via the:
- thalamus: glutaminergic neurones to cortex
- hypothalamus: histaminergic neurones to cortex
- basal forebrain nuclei: receive cholinergic input from RF and project cholinergic neurones to cortex

5

How is level of consciousness assessed?

Glascow Coma Scale (GCS) - assesses:
1. eye opening (spontaneous, response to speech, nil)
2. motor response (obeys, localises, withdraws, abnormal flexor response, extensor response, nil)
3. verbal response (oriented, confused conversation, incomprehensible sound, nil)

Electroencephalograms

6

Do neurones fire synchronously when asleep or awake?

When asleep

7

Describe the wave pattern seen on EEG when awake with eyes open and with eyes closed.

Awake with open eyes = beta waves
- high frequency (50 Hz)
- irregular due to complex processing

Awake with eyes closed = alpha waves
- lower frequency (10 Hz)
- more regular due to deprivation of input

8

Describe the wave pattern seen on EEG during the stages of sleep.

Stage 1
- background alpha waves (10 Hz)
- occasional theta waves (5 Hz)

Stage 2/3
- background of theta waves (5 Hz)
- occasional sleep spindles (short period of increased thalamus activity stimulating cortex)
- occasional K complexes (intrinsic cortical rate)

Stage 4
- delta waves (slow intrinsic cortical rate, high amplitude due to synchronicity of neuronal firing)

REM sleep
- beta waves - dreaming provides visual input to cortex

9

where are the neurones located for REM sleep located?

pons

10

Describe the state of arousal seen in REM sleep

- EEG activity similar to that seen during arousal (beta waves)
- person difficult to rouse due to strong inhibition of thalamus
- muscle tone in most of body is lost due to descending inhibition of LMNs by glycinergic fibres arising from the reticular formation and running down the reticulospinal tracts
- eye movements and some other cranial nerve functions are perserved (e.g. nocturnal bruxism)
- autonomic effects are seen inc. penile erection and loss of thermoregulation

11

describe 3 disorders of consciousness

1. Persistent vegetative state
- widespread cortical damage
- various (disordered) EEG patterns detectable
- unarousable and unresponsive to pyschologically meaningful stimuli but with some spontaneous eye opening (can even localise to stimuli via brainstem reflexes)
- sleep-wake cycle detectable

2. Coma
- widespread brainstem and cortical dysfunction
- various (disordered) EEG patterns detectable
- unarousable and unresponsive to pyschologically meaningful stimuli
- no sleep-wake cycle detectable

3. Brain death
- widespread cortical and brainstem damage
- flat EEG