The reticular formation
• Reticular Formation
Diffused mass of neurons and nerve fibers forming an ill-defined
meshwork of reticulum in the central portion of the brainstem.
 loosely arranged neuron cell bodies intermingled with bundles of
axons
 Various nuclei:
1) Nuclei of medullary reticular formation
2) Nuclei of pontine reticular formation
3) Nuclei of midbrain reticular formation

It receives and integrates input from all regions of the
central nervous system and processes a great deal of neural
information.
THE RETICULAR FORMATION (cont.)
RF is formed of large number of neurons
present through the entire brainstem, it
extends upward to the level of the thalamus
and downward to be continuous with the
interneurons of the spinal cord.
Locations of the reticular and
vestibular nuclei in the brain stem
THE RETICULAR FORMATION (cont.)
Afferent projection
1.
All sensory pathways (general or special
sensations)
2.
3.
4.
5.
6.
Cerebral cortex
cerebellum
Basal ganglia(corpus striatum)
Vestibular nuclei, visual pathway
Thalamus, Subthalamus and
Hypothalamic nuclei
THE RETICULAR FORMATION
(cont.)
Efferent projection:
1. Reticulobulbar and reticulospinal tracts
2. descending pathway to sympathetic and
parasympathetic outflow of ANS
3. cerebellum
4. Basal ganglia(corpus striatum)
5. Thalamus, Subthalamus and
Hypothalamic nuclei

Connections of Reticular
Formation
Fig. 1 -Afferent connections of
reticular formation
Fig. 2 – Efferent connections
of reticular formation
Functional divisions of Reticular Formation
Ascending Reticular Activating System - ARAS

the reticular activating
system (RAS) is an area of
the brain (including the
reticular formation and its
connections) responsible for
regulating arousal and sleepwake transitions.
Receives fibers from the
sensory pathways via long
ascending spinal tracts.
 Alertness, maintenance of
attention and wakefulness.
 Emotional reactions, important
in learning processes.
 Tumor or lesion – sleeping
sickness or coma.

Fig.3 – Brain section.
Functions
1.
2.
3.
4.
5.
6.
Control of skeletal muscles
Control of somatic and visceral sensations
Control of ANS
Influence the biologic clock
The reticular activating system
Control of endocrine nervous system
Vestibulospinal and reticulospinal tracts
descending in the spinal cord to excite
(solid lines) or inhibit (dashed lines) the
anterior motor neurons that control the
body’s axial musculature

Damage to RF persistent unconsciousness
and even coma
Sleep
Sleep is defined as changed state of
consciousness from which the person can
be aroused by sensory or other stimuli, it is
facilitated by reducing sensory input and
by fatigue.
Coma is unconsciousness from which
the person cannot be aroused.