Neuro13 - The Brainstem & Consciousness

Question 1

5 features of the neural components required for consciousness

Cerebral Cortex
Reticular Formation
Positive Feedback
Reticular Formation (RF) Outputs to the Cortex x3
Other Reticular Formation Outputs

Answer 1

1. ) Cerebral Cortex - where conscious thoughts arise
   - receives many inputs including the reticular formation
2. ) Reticular Formation - keeps the cortex awake
   - esp. reticular activating system (RAS) in brainstem
3. ) Positive Feedback - cortex and reticular formation are connected by reciprocal excitatory projections
   - this creates a positve feedback loop
   - +ve FB loops are seen in binary outcomes (e.g. sleep/awake, ovulating/not ovulating etc.)
4. ) Reticular Formation (RF) Outputs to the Cortex
   - RF (excitatory (ACh) projections) –> 3 relay nuclei:
   - basal forebrain: excitatory (ACh) fibres
   - hypothalamus: excitatory (histamine) fibres
   - thalamus: excitatory (glutamate) fibres
5. ) Other Reticular Formation Outputs
   - RF sends projections down to the spinal cord
   - this is responsible for maintaining muscle tone

Question 2

3 components in the glasgow coma scale (GCS)

Eye Opening x4
Motor Response x6
Verbal Response x5

Answer 2

1. ) Eye Opening - 4: spontaneous
   - 3: response to speech: ↓cortex, normal brainstem
   - 2: response to pain: ↓↓cortex, brainstem preserved
   - 1: no response: damaged brainstem +/- cortex
2. ) Motor Response - 6: obeys commands
   - 5: localises to stimuli, ↓higher cortical function but still connections working from sensory to motor cortex
   - 4: withdraws to pain: physiological reflex is present
   - 3: flexor response to pain, lesion above the level of the red nuclei, response still semi-physiological
   - 2: extensor response to pain, lesion below the red nuclei, not a physiological response
   - 1: no response to pain: damage to brainstem +/- cortex
3. ) Verbal Response - 5: oriented in time/place
   - 4: confused conversation, ↓higher cortical function but language centres are still functioning adequately
   - 3: inappropriate words, damaged language centres
   - 2: incomprehensible sounds, cortical damage
   - 1: no response: damage to brainstem +/- cortex

Question 3

6 cycles of sleep

Awake w/ Eyes Open
Awake w/ Eyes Closed
Stage 1 Sleep
Stage 2/3 Sleep
Stage 4 Sleep
REM Sleep

Answer 3

1. ) Awake w/ Eyes Open
   - ß waves: irregular, 50Hz
2. ) Awake w/ Eyes Closed
   - alpha waves: regular, 10Hz
   - removal of a sensory input leads to synchrony so the waves become regular
3. ) Stage 1 - alpha + theta
   - background alpha waves + interspersed theta waves
   - theta waves are regular at around 5Hz
4. ) Stage 2/3 - theta + sleep spindles + k-complexes
   - background of theta + interspersed others:
   - sleep spindles: high frequency bursts from thalamus
   - k-complexes: ‘intrinsic rate’ of the cortex
5. ) Stage 4
   - delta waves: regular, 1Hz (related to k-complexes)
6. ) REM Sleep - where dreaming occurs
   - EEG similar to a conscious patient (similar to ß waves)
   - very difficult to wake due to strong thalamic inhibition

Question 4

Neural Mechanism of non-REM Sleep

4 features of REM sleep

Initiation
Muscle Tone
CN Functions
Autonomic Nervous System

Answer 4

Neural Mechanism of non-REM Sleep - complex

• deactivation of RAS and inhibition of the thalamus
• deactivation caused by removal of sensory inputs (fewer positive influences on positive feedback loop)

1.) Intiation - by neurones in the pons, active process

2. ) Muscle Tone - decreased
   - due to glycinergic inhibition of lower motor neurones
3. ) CN Functions - some can be preserved
   - eye movements: oculomotor, trochlear, abducens
   - teeth grinding: trigeminal
4. ) Autonomic Nervous System - is still active
   - e.g. penile erection, loss of thermoregulation

Question 5

3 sleep disorders

Insomnia
Sleep Apnoea
Narcolepsy

Answer 5

1.) Insomnia - caused by underlying psychiatric disorder

2. ) Sleep Apnoea - compression of airways during sleep
   - caused by excess neck fat
   - frequent waking and excessive daytime sleepiness (most common cause)
3. ) Narcolepsy - falling asleep at inappropriate times
   - brain unable to regulate sleeping and waking patterns
   - caused by mutations in the orexin/hypocretin gene
   - orexin is a neuropeptide that regulates arousal, wakefulness, and appetite

Question 6

4 disorders of consciousness

Brain Dead
Coma
Persistent Vegetative State (PVS)
Locked In Syndrome

Answer 6

1. ) Brain Dead - flat EEG
   - widespread cortical and brainstem damage
2. ) Coma - disordered EEG patterns detectable
   - widespread cortical and brainstem damage
   - unarousable and unresponsive to psychologically meaningful stimuli, no sleep-wake cycle
3. ) Persistent Vegetative State (PVS) - disordered EEG
   - widespread cortical damage
   - like a coma but with spontaneous eye opening
   - can localise to stimuli via brainstem reflexes
   - sleep-wake cycle detectable
4. ) Locked In Syndrome - eye movements preserved, all other somatic motor functions lost from the pons down
   - due to basilar/pontine artery occlusion