Brain systems & neurotransmitters

Brain Systems

1. The Hypothalamus: The "Central Director"
The suprachiasmatic nucleus (SCN) in the hypothalamus is particularly crucial. This small area functions as our internal clock and regulates our circadian rhythm (sleep-wake cycle): the 24-hour rhythm that determines when we are sleepy or alert.
• Disruption of the SCN (for example, due to irregular sleep behavior or too much blue light in the evening) can cause sleep problems.

2. The Brainstem: The Switch Between Sleep and Wakefulness The brainstem, particularly the pons and medulla, regulates the transition between wakefulness, non-REM sleep, and REM sleep.
• These areas send signals to the cerebral cortex, ensuring that we are not constantly awake.

3. The thalamus: a sensory filter
During sleep, the thalamus acts as a gatekeeper: it filters out sensory information (sight, hearing, smell, taste, touch) so we don't constantly wake up. Insomnia can disrupt this filtering function.

4. The pineal gland: the melatonin factory. The pineal gland produces melatonin as soon as it gets dark. This hormone tells your body it's time to sleep. A deficiency or disrupted release (for example, due to night shifts or jet lag) can disrupt your sleep pattern.

Neurotransmitters

1. GABA (gamma-aminobutyric acid)
Where: Widely distributed throughout the brain, especially in the hypothalamus (including the ventrolateral preoptic nucleus, VLPO).
Role: GABA is the primary inhibitory neurotransmitter. Neurons in the VLPO send GABA to inhibit the "awake neurons" in the brainstem and hypothalamus, causing you to fall asleep and stay asleep.

2. Orexin (hypocretin)
Where: Synthesized in the lateral hypothalamus.
Role: Orexin keeps you awake by activating arousal networks in the brainstem. A deficiency of orexin causes narcolepsy (sudden sleep attacks); an overactive system can actually promote insomnia.

3. Serotonin
Where: Synthesized in the raphe nuclei, a group of nuclei in the brainstem (particularly the dorsal and median raphe).
Role: Serotonin helps regulate the sleep-wake cycle and is a precursor to melatonin. It plays a dual role: it promotes sleep onset, but in certain circuits, it can also support wakefulness.

4. Dopamine
Where: Primarily in the substantia nigra and the ventral tegmental area (VTA) in the midbrain.
Role: Dopamine stimulates alertness and motivation. Excessive dopamine activity can make falling asleep difficult. Inhibition of dopamine can cause drowsiness.

5. Norepinephrine
Where: Primarily produced in the locus coeruleus (LC) in the pons.
Role: Norepinephrine increases vigilance and attention. The activity of the LC almost completely stops during REM sleep—this is necessary for being able to "sit" in dreams without waking up.

6. Acetylcholine
Where: Produced by neurons in the pontine tegmentum (pons) and basal forebrain.
Role: Acetylcholine is high during both wakefulness and REM sleep. It plays a key role in the transition to and maintenance of REM sleep.

How do the neurotransmitters work together?
*GABA inhibits active wakefulness systems such as orexin, dopamine, and norepinephrine.
*Orexin ensures that dopamine and norepinephrine remain active -> increased alertness.
*During REM sleep, acetylcholine neurons are active, while norepinephrine and serotonin are "off."

Sleep problems often arise because the delicate interaction between these brain areas and neurotransmitters becomes unbalanced. Factors such as stress, irregular sleep patterns, light exposure, medications, or mental illnesses can disrupt this delicate balance.

By better understanding which systems and substances are involved, we can search for more targeted solutions – ranging from lifestyle changes to therapies that target specific neurotransmitters.