The document discusses the role of the reticular activating system (RAS) in regulating wakefulness and sleep transitions, detailing its anatomical components and neurotransmitter functions. It also outlines various sleep centers in the brain, including their secretions and areas of action, and introduces the retino-hypothalamic pathway as a key player in circadian rhythm regulation. Additionally, factors interfering with sleep, such as adenosine and specific prostaglandins, are highlighted.

1. BIOKAMIKAZI | YANAMALA VIJAY RAJ
1 SLEEP WAVES
RAS (reticular activating system) is a set of connected nuclei responsible for regulating
wakefulness and sleep wake transitions. RAS has both cholinergic and adrenergic components.
Anatomical components of RAS are
• Mid-brain reticular formation,
• Dorsal hypo-thalamus,
• Thalamic intra laminar nuclei,
• Tegmentum.
Cholinergic
 Neuro-transmitters having quaternary ammonium salts,
 Present in acetylcholine and functions with inositol and basic constituent of lecithin,
 Prevents fat deposition in liver,
 Parasympathetic system communicates via cholinergic pathway.
Adrenergic
 Working on adrenaline or nor-adrenaline,
 Adrenalic nervous system as part of autonomous system,
 No role in modulating activity of RAS neurons.
Reticular formation by
Visual impulse,
Ascending sensory tract,
Auditory impulse ,
Descending motor.
Fig7: Reticular formation
Reference: http://www.daviddarling.info/encyclopedia/R/reticular_formation.html

2. BIOKAMIKAZI | YANAMALA VIJAY RAJ
2.1 SLEEP CENTRES
2.1.1 Locus coeruleus
It secrets norepinephrine,
Area of action: Hypothalamus, thalamus, cerebellum.
2.1.2 Substantia nigra and ventral tegmental area
It secrets dopamine,
Area of action: Basal nuclei, prefrontal cortex.
2.1.3 Raphe nuclei
It secrets serotonin,
Area of action: Basal nuclei, cerebellum.
2.1.4 Pontine nuclei
It secrets acetyl-choline,
Area of action: Fornix, cingulate gyrus.
Fig8: Neuromodulator Systems

3. BIOKAMIKAZI | YANAMALA VIJAY RAJ
2.1.5 Medullary synchronization area
May stimulate the Raphe nuclei,
Area of action: nuc. tractus solitarius level.
2.1.6 Encephalic sleep areas
Area of action:
I. Rostral of hypothalamus, especially the supra-chiasmatic area,
II. Intra-laminar and anterior thalamic nuclei.
2.1.7 Basal forebrain sleep area
Area of action: Pre-optic area and Broca’s diagonal band.
2.2 Major centers for sleep and factors interfering sleep
Location Function
Thalamus Cortical activation
Sleep spindle
EEG synchronization
Hypo-thalamus Sleep/watch switch
SCN Circadian clock
Brain-stem Ascending cortical activation
REM/ SWS switch
Factor Function
adenosine Inhibits cholinergic neurons of RAS which
stimulate cortex
PgD2 (Prosta-glandin D2) Increase sleep tendency
Hypothalamus secrets it
PgE2 (Prosta-glandin E2) Secreted by hypothalamus
IL-1 Immunological role
Sleep inducing factor
Muramil peptide Cytokine activation

4. BIOKAMIKAZI | YANAMALA VIJAY RAJ
2.3 RETINO-HYPOTHALAMIC PATHWAY
The retino-hypothalamic tract (RHT) is a photic neural input pathway involved in the circadian
rhythms of mammals. The origin of the retino-hypothalamic tract is the intrinsically
photosensitive retinal ganglion cells (ipRGC), which contain the photo pigment melanopsin. The
axons of the ipRGCs belonging to the retino-hypothalamic tract project directly, mono-
synaptically, to the supra-chiasmatic nuclei (SCN) via the optic nerve and the optic chiasm.
Fig9: Retino-hypothalamic tract
Reference: www.neurology.org