Neurobiology of sleep*

Link to session recording and Summary of Live CME Chitchat 7 dated 08.11.2020

on *Neurobiology of sleep*

(Please follow the page for future updates)

Summary of Chitchat 7:

Neurobiology (in general) broadly encompasses six aspects

(i) Neuroanatomical structure, (ii) Neurophysiological function, (iii) Evolutionary biology, (iv) Molecular correlates, (v) Body correlates and (vi) Neurochemistry.

Sleep has 3 primary functions viz

(a) restorative function, (b) energy conservation, (c) immune function regulation. So sleep is not only meant for restorative or ‘taking a break’ function. It has certain active roles to play like improving cognition and consolidation of memory.

Evolutionary biology of sleep describes the various sequential transitions like locomotor behaviour > endocrine control > fast switching sleep system > evolution of inhibitory & active sleep > sleep inducing neurons & circuits controlling them.

4 Rs of sleep – restoration, regeneration, rejuvenation, re-cognition. Like during servicing of a car, engine oil, brake oil, gear oil, air filter, ac is checked mechanically till the car functions as new. Brain does it by Sleeping.

Sleep is not equal to

rest, every neuron undergoes replenishment, regeneration, repaired, on and off, different parts at different times.

Decision to Sleep is taken by the Sleep network – Insular – ACC- Pons, Hypothalamus – SCM – Pineal ( ACC primarily). Again the same network makes the person awake.

*Flip-flop circuit:* Either sleep neurons are active & inhibit wakefulness neurons or the wakefulness neurons are active and inhibit sleep neurons

NREM control > Passive, REM control> Active. Three major pathways (Dorsal, Ventral and orexigenic).

Dorsal wakefulness promoting network (cholinergic),

Ventral wakefulness promoting network (monoaminergic) &

Orexinerenic pathway (damaged in Narcolepsy).

The flip-flop circuit with activation of Brain stem & forebrain arousal system (ACh, NE, 5HT, Histamine) and inhibition of sleep-promoting region in vlPOA (ventrolateral preoptic atrea) determines the motivation to stay awake.

REM off (vlPAG, ventrolateral periaquiductal gray matter) and REM on (SLD, Sublaterodorsal nucleus) make up the REM sleep flip-flop system.

Sleep promotion is initiated by

(i) Preoptic network, (ii)Medulla=brainstem network &

(iii) Basal forebrain network (damage of which causes irreversible coma).

Another network k/a Insulo-cingular network projects from rostral pons and medulla & determines human consciousness.

Sleep disorders progresses to cause neuronal degeneration and can cause disease specific symptoms.

There are many circuits, centers and neurotransmitters involved in the maintenance of sleep wake cycle.

Various external (environmental) and internal factors (dietary, disease, medication) are responsible for sleep disorders.

🙏🏻🙏🏻

Team Live CME Psychiatry

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