Dense network of neurons and nerve fibers found in
Core of brainstem
Indinstinct , not well defined anatomically.
50-80 nuclear masses
It can be: Midbrain, Pontine and Medullary RF.
Consists of :
Aggregates of Neurons
Afferent and Efferent connections.
They receive afferents from spino-reticular tracts.
Fibers from this part project upwards as Reticular
Fibers from this part project downwards as medial
and lateral reticulospinal tracts.
Also called ARAS from brain stem RF.
Also receives collaterals from:
Trigeminal, auditory , visual and olfactory pathway
From RAS fibers go to non-specific thalamic
nuclei(intralaminar and midline nuclei)
From the thalamus the fibers are projected diffusely and
non specifically to whole cortex.
Some fibers bypass the thalamus to project to whole
RAS is non specific system since it can be stimulated by
any sensation from collaterals.
It also receives facilitatory feedback impules from motor
cortex and inhibitory feedback impulses from limbic
Functions of ARAS:
Facilitatory to central neurons –increases excitability.
Wakefulness and alertness
Beta rhythm in ECG.
Lesions in RAS-Sleep and coma
Benzodiazepines and babituraes prevent synaptic
transmission in RAS.
Neurotransmitters of Reticular formation.
Cholinergic neurons : mid brain and pons to cortex
Adrenergic neurons: whole of RF to thalamus to cortex
Nor adrenergic neurons: locus coerulus to cerebellum
Dopaminergic neurons : midbrain RF to basal ganglia
Serotonergic neurons: Raphe nuclei to thalamus,
cerebral cortex , thalamus and limbic system
From raphe nuclei to spinal cord (control the transmission
Sleep wakefulness: serotonin-secreting neurons in
raphe nuclei mediate non-REM sleep
Conditioning and learning: Neural substrate
Selective attention and sensory inattention:
Control of muscle tone and regulation of postural
reflex changes: RF modulates the tone of extensor
Pontine RF has excitatory and Medullary reticulospinal
tract has inhibitory influence on extensor muscle tone.
Cortical neurons Through Visceral regulating centers
influences the autonomic functions
Modulation of Pain: Raphe nuclei fibers going to
spinal cord (substantial gelatinosa) modulate the
perception of pain.
Control of neuroendocrine system: control the
neuroendocrine system in hypothalamus.