Chapter 33 Main Points

🔑 Key Definitions

          Norepinephrine (NE): Monoamine neurotransmitter involved in arousal, attention, mood, and stress response

          Locus Coeruleus: Small nucleus in pons; main source of NE in brain; projects widely via dorsal bundle

          A6 Nucleus: Another name for locus coeruleus; contains noradrenergic neurons

          Alpha/Beta Receptors: Two main classes of NE receptors with different effects and distributions

🧠 Norepinephrine Synthesis

Shares pathway with dopamine: Phenylalanine → Tyrosine → DOPA → Dopamine → Norepinephrine
Dopamine Beta-Hydroxylase: Enzyme that converts dopamine to norepinephrine
Only in noradrenergic neurons: Need specific enzyme to go beyond dopamine

📊 Major NE Pathways

Locus Coeruleus (A6): Pons nucleus that projects throughout brain via dorsal bundle
Dorsal Bundle: Ascending pathway carrying NE to cortex, hippocampus, cerebellum
Lateral Tegmental System: Additional NE pathway from medulla
Wide Distribution: NE neurons project to virtually all brain regions

📊 NE Receptors & Functions

Alpha Receptors: α1 (excitatory), α2 (often inhibitory/autoreceptors)
Beta Receptors: β1, β2, β3 subtypes; involved in arousal and energy mobilization
Arousal: Increased alertness, vigilance, attention
Sleep-Wake: High NE during waking, low during sleep
Mood: Low NE linked to depression
Motivation: Goal-directed behavior, effort

💡 Exam Tips

NE synthesis adds one step beyond dopamine (needs dopamine beta-hydroxylase)
Locus coeruleus = A6 nucleus = main NE source in brain
Remember: Locus coeruleus is in the PONS (part of hindbrain)
NE = arousal and attention (active during waking, quiet during sleep)
Alpha and beta receptors - know these are NE receptor types
Depression linked to low NE (and serotonin) - many antidepressants increase NE