![• References
• 1.
• Bebin J. The cerebellopontile angle, the blood supply of the brain stem and the reticular
formation. II. Anatomical and functional correlations relevant to surgery of acoustic tumors.
Henry Ford Hosp Med J. 1968 Summer;16(2):163-83. [PubMed]
• 2.
• Wang D. Reticular formation and spinal cord injury. Spinal Cord. 2009 Mar;47(3):204-12. [
PubMed]
• 3.
• Horn AK. The reticular formation. Prog Brain Res. 2006;151:127-55. [PubMed]
• 4.
• Humphries MD, Gurney K, Prescott TJ. The brainstem reticular formation is a small-world,
not scale-free, network. Proc Biol Sci. 2006 Feb 22;273(1585):503-11. [PMC free article] [PubMed]
• 5.
• Milsom WK, Chatburn J, Zimmer MB. Pontine influences on respiratory control in
ectothermic and heterothermic vertebrates. Respir Physiol Neurobiol. 2004 Nov 15;143(2-
3):263-80. [PubMed]](https://image.slidesharecdn.com/reticularformation-250725071632-5a3f78a4/85/Reticular-formation_nuclei_afferent_efferent-20-320.jpg)
![• 6.
• Martins I, Tavares I. Reticular Formation and Pain: The Past and the Future. Front
Neuroanat. 2017;11:51. [PMC free article] [PubMed]
• 7.
• Büttner-Ennever JA, Büttner U. Neuroanatomy of the oculomotor system. The reticular
formation. Rev Oculomot Res. 1988;2:119-76. [PubMed]
• 8.
• Stiles J, Jernigan TL. The basics of brain development. Neuropsychol Rev. 2010 Dec;20(4):327-
48. [PMC free article] [PubMed]
• 9.
• Konan LM, Reddy V, Mesfin FB. StatPearls [Internet]. StatPearls Publishing; Treasure Island
(FL): Jul 24, 2023. Neuroanatomy, Cerebral Blood Supply. [PubMed]
• 10.
• Jang SH, Chang CH, Jung YJ, Kwon HG. Hypersomnia due to injury of the ventral ascending
reticular activating system following cerebellar herniation: A case report. Medicine
(Baltimore). 2017 Jan;96(1):e5678. [PMC free article] [PubMed]](https://image.slidesharecdn.com/reticularformation-250725071632-5a3f78a4/85/Reticular-formation_nuclei_afferent_efferent-21-320.jpg)
Reticular formation_nuclei_afferent_efferent
- 1. RETICULAR FORMATION , Dr. E. Muralinath, Dr. C. Kalyan Chakravarth, Dr. M. Guruprasad, Dr. K. Sravani Pragna, Dr. P. Manjari, Dr. D. Kusumalatha, Dr. K. Sridevi , Dr. Ch. Ramya Sudha and Dr. R. Gnana Lahari
- 2. • DEFINITION • Reticular formation is a diffused mass of neurons as well as nerve fibers, which establish an ill-defined meshwork of reticulum in central portion of the brainstem. • SITUATION OF RETICULAR FORMATION • Reticular formation is located in brainstem. It expands downwards into spinal cord and upwards up to thalamus and subthalamus. • ORGANIZATION OF RETICULAR FORMATION • Reticular formation is made by 5 groups of nuclei. All these nuclei are structurally and functionally distinct. • 1. RAPHE GROUP • A) Raphe group of nuclei are located along the midline of the brainstem establishing a continuous column. • B) Raphe nuclei secrete serotonin (5-hydroxytryptamine), which is an inhibitory neurotransmitter. • 2. PARAMEDIAN GROUP • A) Paramedian group includes nucleus reticularis paramedianus as well as pontine reticulotegmental nucleus. • B) These nuclei are associated with motor functions.
- 3. • 3. LATERAL GROUP • A) Lateral group of nuclei are located in the lateral one third of the tegmentum. • B) It contains nuclei along with small (parvocellular) cells. • C) Neurons of these nuclei obtain sensory signals from the cranial nerves, cerebellum and spinal cord. • 4. MEDIAL GROUP • A) Medial group of nuclei are located in the medial two third of the tegmentum. • B) It contains nucle along w with small cells and giant (gigantocellular) cells. • C) Nuclei of this group lead to the formation of the major output of the reticular formation and send fibers to the hypothalamus, thalamus and spinal cord. • D) These nuclei are concerned with motor functions. • 5. INTERMEDIATE GROUP • A) Intermediate group of nuclei are observed only in the medulla. • B) It is located between the lateral and medial groups of nuclei. • C)These nuclei are associated with autonomic regulation of respiration, heart rate and blood pressure
- 4. • CONNECTIONS OF RETICULAR FORMATION • AFFERENT CONNECTIONS • Reticular formation obtains collaterals from almost all the ascending sensory pathways. It also obtains fibers from different parts of the brain : • 1. Optic pathway • 2. Olfactory pathway • 3. Auditory pathway • 4. Taste pathway • 5. Spinal and trigeminal pathways carrying touch sensation • 6. Pathways for pain, temperature, vibration and kinesthetic sensations • 7. Cerebral cortex • 8. Cerebellum • 9. Corpus striatum • 10. Thalamic nuclei.
- 5. • EFFERENT CONNECTIONS • Reticular formation sends fibers to the following parts of central nervous system : • 1. Cerebral cortex • 2. Diencephalon: Thalamus, hypothalamus and subthalamus • DIVISIONS OF RETICULAR FORMATION • Reticular formation is categorized into three divisions dependent upon the location in brainstem: • A. Medullary reticular formation • B. Pontine reticular formation • C. Midbrain reticular formation. • Each division of reticular formation consists of its own collection of nuclei • NUCLEI OF MEDULLARY RETICULAR FORMATION • 1. Lateral reticular nucleus • 2. Ventral reticular nucleus • 3. Dorsal reticular nucleus • 4. Gigantocellular reticular nucleus • 5. Paragigantocellular reticular nucleus • 6. Paramedian reticular nucleus • 7. Parvocellular reticular nucleus • 8. Magnocellular reticular nucleus.
- 6. • NUCLEI OF PONTINE RETICULAR FORMATION • 1. Nucleus reticularis pontis oralis • 2. Nucleus reticularis pontis caudalis • 3. Locus ceruleus nucleus • 4. Subceruleus reticular nucleus • 5. Tegmenti pontis reticular nucleus • 6. Pedunculopontine reticular nucleus • 7. Nucleus reticular cuneiformis. • •
- 7. • NUCLEI OF MIDBRAIN RETICULAR FORMATION • 1. Red nucleus • 2. Nucleus tegmental pedunculopontis • 3. Nucleus reticular subcuneiformis. • . • FUNCTIONS OF RETICULAR FORMATION • Based on functions, reticular formation along with its connections is categorized into two systems: • A. Ascending reticular activating system • B. Descending reticular system. •
- 8. • ASCENDING RETICULAR ACTIVATING SYSTEM • Ascending reticular activating system (ARAS) starts with lower part of brainstem, expands upwards through pons, midbrain, thalamus and finally projects throughout the cere bral cortex. It projects into cerebral cortex in two ways: • 1. Via subthalamus • 2. Via thalamus. • The ARAS obtains fibers from the sensory pathways via long ascending spinal tracts. • Functions of ARAS • 1. The ARAS is associated with arousal phenomenon, alertness, maintenance of attention and wakefulness. Hence, it is known as ascending reticular activating system. An activation of midbrain reticular formation produces wakefulness by generalized activation of entire brain including cerebral cortex, thalamus, basal ganglia and brainstem. Any type of sensory impulses namely impulses of proprioception, pain, auditory, visual, taste and olfactory sensations cause sudden activation of the ARAS producing arousal phenomenon in animals • and human beings. Even the impulses of visceral sensations stimulate this system. Sympathetic stimulation and adrenaline cause arousal by influencing • midbrain. • 2. The ARAS also causes emotional reactions • 3. The ARAS plays an important role regarding the regulation of the learning processes as wdevelopment of conditioned reflexes.
- 9. • Mechanism of Action of ARAS • Impulses of all the sensations arrive cerebral cortex through two channels: • 1. Classical sensory pathways • 2. Ascending reticular activating system. • 1. Classical or specific sensory pathways • A) Classical sensory pathways are the pathways, which transmit the sensory impulses particularly from receptors to cerebral cortex via thalamus. • B)Some of the pathways carry impulses of a particular sensation only. • C)For example, auditory stimulus transmitted by auditory pathway arrives the auditory cortex via thalamus and leads to perception of sound. • D) Such classical sensory pathways are termed as specific sensory pathways.
- 10. • 2. Ascending reticular activating system or non-specific sensory pathway • A) All the sensory pathways send collaterals to ARAS, which is a multisynaptic relay system. B)These collaterals project in diffused areas of ARAS. • C) So, the transmission of sensory impulses takes place via the collaterals and arrive different parts of ARAS. • D) It also arrives afferents from spinal cord in a direct manner in the form of spinoreticular tract. • E)ARAS in turn sends the impulses to almost all the areas of cerebral cortex and other parts of brain. • F) Hence, this pathway is termed as the non-specific sensory pathway. • G) Non-specific projection of ARAS into the cortex is associated with the arousal, alertness and wakefullness. • H) Sensory impulses transmitted directly to cortex via classical pathway causes perception of only the particular sensation. Whereas, the impulses transmitted to cortex via ARAS do not cause the perception of any particular sensation, but cause the generalized stimulation of almost all the areas of cerebral cortex as well as other parts of brain.
- 11. • I) This results in reactions of arousal, alertness and wakefulness. • J) The ARAS is in turn regulated by the feedback signals from cerebral cortex. • K) Also, an inhibitory system regulates the activities of ARAS. • L) Inhibitory system is related to posterior hypothalamus, intralaminar and anterior • thalamic nuclei and medullary area at the level of tractus solitarius. • Tumor or lesion in ARAS results in sleeping sickness or coma. The impact of head injury on ARAS also causes coma.
- 12. • DESCENDING RETICULAR SYSTEM • Descending reticular system is linked to reticular formation in brainstem, reticulospinal tract and reticular formation in spiral cord. • It changes the activities of spinal motor neurons. • Functionally, descending reticular system is categorized into two subdivisions : • 1. Descending facilitatory reticular system • 2. Descending inhibitory reticular system. •
- 13. • Descending Facilitatory Reticular System • Descending facilitatory reticular system is observed in upper and lateral reticular formation. Its functions include • i. Facilitation of somatomotor activities • a. Descending facilitatory reticular system regulates muscle tone by exciting the gamma motor neurons in spinal cord; Activation of this area causes enhanced muscle tone • b. It promotes the movements of the body. Activation of this part of reticular system causes exaggerated movements. • c. It plays a role in wakefulness and alertness by stimulating the ARAS. • ii. Facilitation of vegetative functions • Descending facilitatory reticular system is the center for facilitation of the autonomic functions namely cardiac function, blood pressure, respiration, gastrointestinal function and body temperature.
- 14. • Descending Inhibitory Reticular System • Descending inhibitory reticular system is situated in a small area in lower and medial reticular formation. Its functions include: • i. Control of somatomotor activities • a. Descending inhibitory reticular system plays an important role regarding the regulation of muscle tone. By obtaining signals from basal ganglia, it inhibits the gamma motor neurons of spinal cord and reduces muscle tone. Activation • of this area causes decreased muscle tone. • b. It is responsible for smoothness and accuracy of voluntary movements. It maintains the muscular activity by inhibiting the motor neurons of spinal cord. • c. It also regulates the reflex movements. • ii. Control of vegetative functions • Descending inhibitory reticular system is the center for inhibition of several autonomic functions namely cardiac function, blood pressure, respiration, gastrointestinal function and body temperature.
- 15. Fig 1. Reticular Formation - An Overview
- 16. Fig 2. Reticular Formation - Function and Location
- 17. Fig 3. Reticular Formation- Anatomy and Clinical Note
- 18. Fig 4. Reticular Formation and Lymphatic System
- 19. Fig 5. Reticular Formation and Spinal cord Injury
- 20. • References • 1. • Bebin J. The cerebellopontile angle, the blood supply of the brain stem and the reticular formation. II. Anatomical and functional correlations relevant to surgery of acoustic tumors. Henry Ford Hosp Med J. 1968 Summer;16(2):163-83. [PubMed] • 2. • Wang D. Reticular formation and spinal cord injury. Spinal Cord. 2009 Mar;47(3):204-12. [ PubMed] • 3. • Horn AK. The reticular formation. Prog Brain Res. 2006;151:127-55. [PubMed] • 4. • Humphries MD, Gurney K, Prescott TJ. The brainstem reticular formation is a small-world, not scale-free, network. Proc Biol Sci. 2006 Feb 22;273(1585):503-11. [PMC free article] [PubMed] • 5. • Milsom WK, Chatburn J, Zimmer MB. Pontine influences on respiratory control in ectothermic and heterothermic vertebrates. Respir Physiol Neurobiol. 2004 Nov 15;143(2- 3):263-80. [PubMed]
- 21. • 6. • Martins I, Tavares I. Reticular Formation and Pain: The Past and the Future. Front Neuroanat. 2017;11:51. [PMC free article] [PubMed] • 7. • Büttner-Ennever JA, Büttner U. Neuroanatomy of the oculomotor system. The reticular formation. Rev Oculomot Res. 1988;2:119-76. [PubMed] • 8. • Stiles J, Jernigan TL. The basics of brain development. Neuropsychol Rev. 2010 Dec;20(4):327- 48. [PMC free article] [PubMed] • 9. • Konan LM, Reddy V, Mesfin FB. StatPearls [Internet]. StatPearls Publishing; Treasure Island (FL): Jul 24, 2023. Neuroanatomy, Cerebral Blood Supply. [PubMed] • 10. • Jang SH, Chang CH, Jung YJ, Kwon HG. Hypersomnia due to injury of the ventral ascending reticular activating system following cerebellar herniation: A case report. Medicine (Baltimore). 2017 Jan;96(1):e5678. [PMC free article] [PubMed]