Download Reticular formation

Reticular formation
Poster No.:
C-1914
Congress:
ECR 2017
Type:
Educational Exhibit
Authors:
A. R. SIVAJI; TBILISI/GE
Keywords:
Anatomy, Neuroradiology brain, MR, Computer ApplicationsDetection, diagnosis, Biological effects, Outcomes
DOI:
10.1594/ecr2017/C-1914
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Page 1 of 10
Learning objectives
Learning objectives :
1. To know the definition and the area where the reticular formation is present in the brain
because it is diffused area occupying the brain.
2. T o know the group of nuclei, functions, afferents and efferents because the RF is
almost have connections with various part of the brain.
3. To know the nuclei group of the RF involved in various neurological and psychiatric
disorders
Reticular formation is defined as diffuse as diffuse ill-defined mass of intermingled
neurons & nerve fibres occupying the entire core of brainstem
Phylogentically it represents old reticular core of brain & contains vital cardiac &
respiratory centers.
The importanc of RF :
· it regulates level of consciousness & alertness
· regulates respiration, blood pressure, heart rate
· regulates tone of skeletal muscles
· modulates the impulses in pain pathways
The reticular nuclei in brainstem arranged into three longitudinal columns:
1. Median column : lies in midline, termed as raphe nuclei & has three parts, produces
serotonin
a) dorsal raphe nucleus-projects to spinal cord forming pain controlling pathway
b) nucleus raphe pontisc) nuleus raphe magnus-projects to caudal part of sipnal nucleus of V cranial nerve &
influences perception of pain
2. Medial column termed as magnocellular column includes ventral reticular nucleus
(in medulla ), gigantocellularnucleus (in meulla & pons ),oral & cadual ponine nuclei
(in pons ) receive afferents from lateral group & efferents ascend & descend in brain stem
forming polysynaptic pathway
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3. Lateral column termed parvocellular column includes parvicellular nuclei of
medulla & pons, nucleus locus ceruleus of pons & pedunculopontine nucleus of
midbrain
Connections of reticular formation:
Afferent connections : classified into three types :
Afferents from various sensory pathways or systems
-Optic system -through tectoreticular fibres
-Olfactory & limbic system-through descending pathways
-Auditory system- through tectoreticular fibres
-Gustatoty system
-Spinal pathways through spinoreticular fibres
-Trigeminal pathways
Afferents fibres from other parts of CNS
-Cerebellum mainly from contralateral fastigial nucleus
-Basal ganglia mainly from corpus striatum
Thalamus, hypothalamus & subthalamus
Limbic system mainly from septal areas, amygaloid nucleus & hippocampus
Cerebral cortex mainly from motor & sensory areas
Red nucleus, substantia nigra & habenular nuclei
Images for this section:
Page 3 of 10
Fig. 1: Reticular Nuclei Formation
© Textbook of Neuroanatomy by Vishram Singh 2nd Edition
Page 4 of 10
Fig. 2: Tabular Explanation
© Textbook of Human Neuroanatomy Inderbir Singh 9th Edition
Page 5 of 10
Background
Efferent connections :
Autonomic & locomotor control centres of brainstem & spinal cord
Cranial nerve nuclei- dorsal nucleus of vagus
Cerebral cortex indirectly through diencephalic nuclei
Red nucleus, substantia nigra, tectum of midbrain
Functional Divisions of Reticular activating system:
1.Ascending reticular activating system(ARAS)commonly termed as reticular
activating system (RAS).It is believed to be responsible for maintaining a state of
alertness & consciousness
2. Descending reticular system(DRS) consists of descending pathways to
brainstem,lateral & anterior horn cells in the spinal cord.
Functions of Reticular formation
· Maintains the normal state of consciousness or wakefulness through its connections
with cerebral cortex by ARAS
· Regulates respiration,heart rate blood pressure
· Controls muscular activity throughreticulospinal projections to LMN &indirectly by
influencing the activities of cerebellum, red nucleus, substantia nigra, corpus striatum &
cerebral cortex
· Controls receptivity of sensory end organs
· Controls threshold of central sensory pathways
· Regulates endocrine, visceral & emotional functions through its connections with
hypothalamus & limbic lobe
Images for this section:
Page 6 of 10
Fig. 3: Connections of Reticular Formation.
© Textbook of Human Neuroanatomy Inderbir Singh 9th Edition
Page 7 of 10
Findings and procedure details
Cigarette smoking : During pregnancy cigarette smoking produce lasting arousal,
attentional and cognitive deficits in humans. The pedunculopontine nucleus (PPN), as the
cholinergic arm of the reticular activating system (RAS), is known to modulate arousal,
waking and rapid eye movement (REM) sleep. Prenatal exposure to cigarette smoke
induces marked changes in cells in the cholinergic arm of the RAS, making them more
excitable.
Preterm birth induces persistent deleterious effects on arousal and sleep wake cycle
and cortical mechanisms throughout development
In the pontine tegmentum, there is an important center for horizontal gaze. The
coordination of for lateral conjugate gaze is carried out at the pontine level by the
paramedian pontine reticular formation (PPRF). This nucleus, which also has
ipsilateral connections to the abducent (VI) nucleus. These PPRF fibers then ascend in
the MLF to the contralateral oculomotor (cranial nerve III) nucleus. If a lesion extends
into the dorsal-medial aspect of the upper pons, it may interrupt these ascending fibers
in the MLF, resulting in difficulties with conjugate gaze to the side opposite the lesion.
Horner's syndrome-involvement of descending sympathetic pathway in reticular
formation
Coma is a state of unconsciousness- due to inactivity of RAS
In Parkinsonism - Parkinson's disease have significant loss of PPN neurones,
the degeneration of PPN neurones or their dysfunction may be important in the
pathophysiology of locomotor and postural disturbances of parkinsonism.
REM sleep behaviour disorder:Studies conducted showed pedunculopontine nucleus ,
latero dorso tegmental nucleus (LDTN) and several pontine nuclei influence wake-sleep
states .In REM sleep without atonia, lesions to locus ceruleus disrupt the excitatory
connection to mangocellular column disable the hyperpolarization of the alpha spinal
motorneurons. In humans after extensive neurologic evaluations who have suffering from
both idiopathic and symptomatic forms have not identified specific lesions. , The findings
in some patients suggest that diffuse lesions of the hemispheres, bilateral thalamic
abnormalities, or primary brain-stem lesions may result in the RBD.
Schizophrenia : it is characterized by severe sleep wake cycle which includesdecreased
slow wave sleep (SWS),increased rapid eye movement (REM) sleep, fragmented sleep
etc. These abnormalities reflects an overactivity of pendunculopontine nucleus (PPN)
of reticular activating system. Many studies emphasized the relationship of increased
cholinergic output of PPN and the negative symptoms in schizophrenia.
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Post traumatic stress syndrome: Patients with this syndrome have significant 50%
decrease in the number of locus coeruleus (LC) neurons,which results in increased
disinhibition of the PPN.
Depression, autism, attention deficit disorder : The exact role of the RAS in the above
mentioned disorders are not identified so far. However, it is said that any neurological
or psychiatric disease that manifests disturbances in arousal and sleep-wake cycle
regulation, there will be a corresponding dysregulation of some elements of the RAS.
Alzheimer's disease : Reduction of cholinergic neurons observed in Alzheimer's disease
with dementia
Narcolepsy : Clinically, disturbances in electrical coupling have a effect with a decrement
in synchronization, especially of gamma oscillations, leading to decreased alertness
in narcolepsy. There is significant inhibition of PPN and loss of orein peptides, which
induces daytime sleepiness in narcolepsy.
Normal 0 false false false EN-US X-NONE X-NONE
Conclusion
Many hypothesis were given about the involvement of RF in various neurological and
psychiatric disorders. This educational exhibit is to propose the various possibilities
of involvement of the nuclei group of RF in disorders because it's a complex and
diffused area in brain.The specificity of RF improvise the differential diagnosis and clear
knowledge about it is very important.
Personal information
References
Principles of Neurology 6th Edition by Raymond D.Adams,Maurice Victor,Allan
H.Ropper.
Page 9 of 10
Chp 3:26-30.
Bradley's Neurology in Clinical Practice 6th Edition by Robert B.Daroff,Gerald M.
Fenichel,Joseph Jankovic,John Mazziotta.Chp 28:328-336.
Harrison's
Principle
of
Internal
Medicine
18th
Longo,Fauci,Kasper,Hauser,Jameson,Loscalzo. Chp 22:181-185.
Edition
by
Gray's Anatomy for Students , 3rd Edition by Richard L. Drake, A. Wayne Vogl, and Adam
W.M. Mitchell.
Textbook of Human Neuroanatomy by Inderbir Singh 9th Edition.
Textbook of Clinical Neuroanatomy by Vishram Singh 2nd Edition.
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