Modulatory and arousal systems

Question 1

Specific vs modulatory pathways

Answer 1

• specific = precisely localised. sensory, motor, cognitive processing. fast transmission - ionotropic
• modulatory = diffuse systems. control state of system. non-specific. slow - metabotropic

Question 2

Sleep-wake cycle - Awake vs Asleep

Answer 2

• Awake - thalamic cells relay sensory info to the cortex - fire when stimulated, desynchronised with low amplitude but high frequency
• Asleep - thalamic cell starts to fire bursts of AP in a rhytmic manner - no longer relaying the specific information. When the thalamic nerves start to fire, the inhib. intern. start to control them. - peaks and troughs at regular intervals, high amplitude but low freq.

Question 3

Slow wave sleep

Answer 3

• Stages 3 and 4
• gradual increase in amplitude and reduction in frequency as you move into deeper sleep
• less than 4Hz with a high amp. at deepest sleep
• increase in synchronisation in thalamus and cortex

Question 4

REM sleep - EEG

Answer 4

• EEG looks like you are awake - low amp. and high freq.
• completely limp and paralysed but your eyes move around
• dreaming
• through the night, REM gets longer and NREM gets shorter and shallower

Question 5

Acetylcholine pathway

Answer 5

• Pathways from the pontomesencephalic tegmentum (grey matter in pons and midbrain) go to the basal forebrain, neocortex and hippocampal complex and the thalamus and basal ganglia
• ACh increases response strength and selectivity and increases plasticity of the brain
• causes us to be awake and attentive, increases cognition, learning and memory
• desynchronises thalamic cells > connection to outside world
• a lack of ACh leads to cognitive decline and memory issues
• AChE inhibitors such as Donepezil reduce ACh breakdown (used in AD)

Question 6

NA pathway

Answer 6

• used everywhere, extends in a long stripe from locus coeruleus downwards
• NA increases response amplitude and selectivity
• causes us to be awake and vigilant, alert to new stimuli, increases learning and memory and controls mood
• A lack of NA leads to anxiety and depression
• NA reuptake inhibitors and MAOIs can increase NA levels

Question 7

DA pathway

Answer 7

• Also associated with areas of the thalamus
• Substantia nigra projects to the basal ganglia
• ventral tegmental area projects to the frontal cortex, limbic and related structures (amygdala and nucleus accumbens)
• DA causes us to be awake, alert to rewarding/aversive stimuli, adaptive behaviour
• Too much DA > sz
• Too little > PD

Question 8

Histamine pathway

Answer 8

• released from hypothalamus (tuberomamillary nucleus)
• spreads to the thalamus and cortex
• it excites wake-promoting circuits - makes us awake and alert
• anti-histamines > drowsiness

Question 9

Orexin (hypocretin) pathway

Answer 9

released from hypothalamus and spreads everywhere in brain

• excites wake-promoting circuits, responds to nutritional status and linked to reward centres
• causes us to be awake and exploring, allows energy homeostasis
• low orexin > narcolepsy

Question 10

Serotonin (5-HT) pathway

Answer 10

• released from raphe nuclei to everywhere in brain
• causes quiet waking, appropriate response to stress, mood and helps analgesia pathway
• reduced levels lead to anxiety and depression
• can take SSRIs or MAOIs to reduce anxiety and depression

Question 11

Arousal: From sleep to wake

Answer 11

• Hypothalamus releases orexin and histamine
• increases activation of brainstem
• releases serotonin, ACh and NA > desynchronises EEG
• increases activation of the basal forebrain, which releases more ACh > increased response strength and selectivity
• brain stem lesions > coma

Question 12

Falling asleep

Answer 12

• hypothalamus (ventrolateral preoptic nucleus) releases GABA
• reduces the levels of orexin and histamine released from the hypothalamus and the serotonin, ACh and NA released from the brain stem

Question 13

What activates the Ventrolateral preoptic nucleus?

Answer 13

• Circadian rhythm (SCN)
• tiredness (build up of adenosine
• illness (increase in immune by-products)
• caffiene is an adenosine antagonist > reduces tiredness
• Lesions in GABAergic centre cause insomnia

Question 14

REM Sleep

Answer 14

• increased levels of ACh, with decreased levels of other chemicals
• ACh increases basal forebrain activity among other areas
• increases activity in higher cortical areas > dreaming
• Causes desynchronised EEG (like if awake) however also causes skeletal muscle paralysis

Question 15

Modulatory pathways control cognitive performance

Answer 15

• stimulation of histamine, NA, serotonin, DA and orexin systems in brain

Question 16

Modulatory pathways and mood

Answer 16

• pleasure and rewards - increased stimulation of VTA > increases DA release. Goes to nucleus accumbens. Associated with DA pathways to cortex and limbic structures
• anxiety and depression - decreased activity in brainstem (reduces serotonin and NA levels) and decreased activity in VTA (reduces DA levels). Associated with reduced function in Monoamine pathwyas