Reticular formation
Reticular formation
• Consists a substantial portion of the dorsal part
of the brain stem in which a group of neurons
and netlike fibers. The reticular formation does
not include nuclei of cranial nerves, long tracts
that pass through the brain stem, and those
conspicuous masses.
• The function of reticular formation includes the
sleep arousal cycle, perception of pain, control
of movement, and the regulation of visceral
activity.
Nuclei of Reticular Formation
• Nuclei of the reticular formation
– Precerebellar nuclei
– Raphe nuclei
– The central group of nuclei
– Cholinergeric and catecholamine cell groups
– The lateral parvocellular reticular area
– The parabrachial area
– Superficial medullary neurons
Precerebellar nuclei
• Includes lateral reticular nucleus, the
paramedian reticular nucleus, and the
pontine reticulotegmental nucleus. They
project to the cerebellum. Their functions,
associated with cerebellum are different
from the rest of the reticular nuclei.
Raphe nuclei
• 1. Medullary raphe nuclei Include nucleus raphes
magnus, nucleus raphes pallidus, and nucleus raphe
obscurus.
• Afferent fibers are from the spinal cord, the gracile and
cuneate nuclei, the trigeminal sensory nuclei, and the
periaqueductal gray matter.
• Efferent fibers project to cerebellum, dorsal and ventral
horns of the spinal gray matter, to the trigeminal nucleus,
and to the preganglionic autonomic neurons of the brain
stem and cord.
• Input from the periaqueductal gray matter and projection
to spinal gray matter is responsible for suppressing the
pain awareness.
Raphe nuclei
• 2. Raphe nuclei of the midbrain and rostral pons
• Include nucleus raphes pontis, superior central nucleus,
nucleus raphes dorsalis, and dorsal tegmental necleus
(P185)
• Afferent fibers:
• Precentral cortex, and limbic system (hippocampal
formation, the hypothalamus, the interpeduncular
nucleus, and the ventral tegmental area)
• Efferent fiber:
• Forebrain, cerebellum, and noradrengeric nuclei of the
brain stem
• Function: awareness of pain, and sleep pattern.
Central group of reticular nuclei
• Includes central medullary nucleus and the
gigantocellular nucleus in the medulla, the
caudal and oral pontine reticular nuclei,
cuneiform and subcuneiform nuclei in the
midbrain.
Central group of reticular nuclei
• Afferent fibers:
• From sensory system including spinoreticular tracts,
collateral tracts from spinothalamic tract and
trigeminothalamic tracts, and collateral fibers form
gustatory and auditory system. Visual information is
provided by tectoreticular fibers originate from superior
coliculus. Other afferent fibers are from fastigial nucleus of
the vestibulocerebellum, reticular formation of the
midbrain, cholinergic reticular nuclei, and the premotor
area of the cerebral cortex.
• Efferent fibers:
• To other reticular neurons (like raphe and catecholamine
neurons). Descending fibers constitute the medial
(pontine) and lateral (medullary) reticulospinal tracts.
Ascending fibers: to the intralaminar thalamic neuclei and
the basal cholinergic nuclei of the substantia innominata.
From there, fibers project to whole cortex for
consciousness control and to corpus striatum for motor
control.
Cholinergic and catecholamine nuclei
• Cholinergic nuclei
• Includes the pedunculopontine nucleus and
nearby pontine periventricular gray matter.
• Afferent fibers:
• From pallidum and substantia nigra
• Efferent fibers:
• To central group of pontine and medullary
reticular nuclei, subthalamic nuclei, and corpus
striatum.
• Function: Similar to central group, including
locomotion, consciousness and arousal
Cholinergic and catecholamine nuclei
• Catecholamine nuclei
• Use NE, N and dopamine as
neurotransmitter
• Includes locus coeruleus and other smaller
groups of nuclei
Catecholamine nuclei
• Afferent fibers:
• From central group of reticular nuclei, and the nucleus
prepositus hypoglossi, the latter involves the control of
eye movement. They also receive info from periaquctal
gray matter and other components of the reticular
formation, and from hypothalamus, amygdala, and
prefrontal cortex.
• Efferent fiber:
• Most of them travel in central tegmental tract. To
periaqueductal gray matter, and ascend to hypothalamus,
basal cholinergic nuclei of the forebrain, and the
amygdala. Some fibers end in thalamus, habenular nuclei,
olfactory bulb, hippocampal formation and most of the
neocortex.
• Other fibers descend to preganglionic autonomic neurons
in the medulla and spinal cord
• Function: Modulator of synapses between neurons, also
effects on alertness and reflexes
Parvocellular reticular area
• Afferent fibers:
• From sensory nuclei (trigeminal nuclei)
and cerebral cortex
• Efferent fibers:
• To the motor nuclei of the hypoglossal,
facial, and trigeminal nerves
• Function: reflexes with feeding
Parabrachial area
• includes lateral and medial parabrachial nuclei,
and the Kolliker-Fuse nucleus
• Afferent fibers:
• From solitary nucleus and from the cortex of
insula and adjacent parietal lobe
• Efferent fibers:
• To hypothalamus, preoptic area, intralaminar
thalamic nuclei, and amygdala.
• Function: Relay station for visual sensation
• Kolliker-Fuse nucleus is part of the pneumotaxic
center regulating the respiratory rhythm.
Superficial medullary reticular neurons
• Afferent fibers:
• from spinal cord and solitary nucleus. Include fibers
sending information from chemoreceptor in the carotid
and aortic sinuses. Some of these neurons can respond
directly to changes of pH or carbon dioxide.
• Efferent fibers:
• project to the hypothalamus and preganglionic
autonomic neurons in the medulla and spinal cord.
• Function: regulates cardiovascular and respiratory
activities
Functions of the reticular formation in general
• Sleep and arousal
• Varying level of consciousness is paralleled by changes
in neuronal activities, which can also be expressed in
EEG. We currently believe that ascending activating
system (originate from reticular nuclei to thalamus rather
than to whole cerebral) increases general level of
sensory stimulation thus lead to increased level of
neuronal activities and increased arousal level. The
noradrenergic neurons and histamine secreting neurons
also stimulate arousal level.
• Sleep inducing neurons, like serotonergic neurons of the
raphe nuclei could inhibit thalamus and cerebral function
thus decrease arousal level.
Functions of the reticular formation
• Pain
• A descending inhibitory pathway could
inhibit transmission of pain. Peptide
neurotransmitters (like opiate drugs,
morphine) released at synapses of
periaqueductal gray matter, raphe nuclei,
and dorsal horn of spinal gray matter could
block the pain sensation.
Functions of the reticular formation
• Somatic motor function
• reticulospinal is the major descending pathway
controls the motor movement. Most of the
descending fibers run ipsilaterally to spinal cord
level, some terminate ipsilaterally and others
cross at white commissure of spinal cord to the
contralateral side. Therefore, the reticulospinal
innervation is bilaterally.
• Visceral activities
• Certain regions of reticular formation regulate
visceral functions and breathing.