Reticular formation

Learning objectives
 Reticular formation nuclei
 Reticular pathways
 Physiology of Reticular activating system
 Functions of Reticular formation.

Reticular formation
 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.

Reticular formation
 The neurons have long dendrites and axons.

Reticular formation
NUCLEAR COLUMNS:
Median column:
 Raphe nuclei in midbrain
Median Column:
 MAGNOCELLULAR
 Nucleus gigantocellularis in medulla and pontine
tegmental nuclei.

Reticular formation
 Lateral columns:
PARVOCELLULAR
Central nucleus of medulla and pons

Reticular formation
 Cardiac centers
 Respiratory centers
 Vasomotor centers
 Salivatory centers
 Chemoreceptor neurons.

Reticular formation
 They receive afferents from spino-reticular tracts.
 Fibers from this part project upwards as Reticular
activating system.
 Fibers from this part project downwards as medial
and lateral reticulospinal tracts.

Reticular pathways
Connections of RF:
 Afferent connections
 Efferent connections:
Ascending and Descending projections.

Reticular formation
 Afferents:
Receives afferents from almost all ascending sensory
pathways
 Optic pathway
 Olfactory pathway
 Auditory pathway
 Taste pathway
 Spinal and Trigeminal pathway
 Pain, temperature, vibration and kinesthetic sensation.
 Cerebral cortex
 Cerebellum
 Corpus striatum
 Thalmic nuclei

Reticular pathways
 Cortico-reticulo-spinal pathways:
Cortico-reticulo-cerebellar
 Cortico-reticulo-basal ganglia
 Visceral control pathways: control of respiration ,
heart rate and BP
 RAS-Reticular activating system.

Reticular pathways
 RAS:
Also called ARAS from brain stem RF.
Polysynaptic pathway
Also receives collaterals from:
 Spinothalamic tracts
 Trigeminal, auditory , visual and olfactory pathway
systems.

Reticular pathways
 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
cortex.
 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
system.

Reticular pathways
 Functions of ARAS:
Facilitatory to central neurons –increases excitability.
Wakefulness and alertness
Beta rhythm in ECG.
Applied aspects:
 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
of pain)

Reticular formation
Functions:
 Sleep wakefulness: serotonin-secreting neurons in
raphe nuclei mediate non-REM sleep
 Conditioning and learning: Neural substrate
 Selective attention and sensory inattention:
FILTER
 Control of muscle tone and regulation of postural
reflex changes: RF modulates the tone of extensor
muscles.
Pontine RF has excitatory and Medullary reticulospinal
tract has inhibitory influence on extensor muscle tone.

Reticular formation
 Autonomic functions:
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.