Functions and Groups in Brain Stem's Reticular Formation, Lecture notes of Neuroscience

Download Functions and Groups in Brain Stem's Reticular Formation and more Lecture notes Neuroscience in PDF only on Docsity! Brain stem Reticular formation Definition
Mass of neurons and nerve fibers extending from the caudal medulla to the rostral midbrain and continuous with the zona incerta of the subthalamus and midline, intralaminar and reticular nuclei of the thalamus
Organized into definite nuclear groups with known afferent and efferent connections
As a whole, the reticular formation comprises a neural system with multiple inputs and multisynaptic system of impulse conduction Reticular nuclei Cuneiform Subcuneifor m Dorsal Raphe (nucleus supratrochlearis) Superior central (Bekhterew) Midbrain Parabrachial Pedunculop ontine Reticulotegm ental Rostral pons– caudal midbrain Reticularis parvocellular is Reticularis pontis caudalis Reticularis pontis oralis Raphe pontisPons Paramedian reticular Raphe magnusRostral medulla caudal pons Reticularis parvocellular is Reticularis lateralis Reticularis giganto cellularis Raphe obscurus Raphe pallidus Medulla LateralMedialParamedianMedian Raphe Reticular formation – summary of functions Purves, et al, Neuroscience, 3rd ed. Median raphe nuclei rostral raphe nuclei → reticular activating system (wakefulness, alertness, and sleep) caudal raphe nuclei → pain mechanisms Descending analgesic pathways activate enkephalin- containing local circuit neurons Purves, et al, Neuroscience, 3rd ed. SER, NA Glu, NP morphine acts here Medial reticular nuclei Gigantocellular nucleus cuneiform & subcuneiform nuclei ascending projections → consciousness and alertness descending projections → motor control Premotor cortex regulates posture via the reticular formation Purves, et al, Neuroscience, 3rd ed. Lateral reticular nuclei
Pedunculopontine – connections with cortex & substantia nigra → locomotor center
Parabrachial nucleus – connections with amygdala, nucleus solitarius, hypothalamus → autonomic function
N. parvocellularis and lateralis constitute the receptive component of reticular nuclei – receive from ascending sensory systems, project to cortex & medial reticular group Reticular formation – summary of functions Purves, et al, Neuroscience, 3rd ed. Reticular formation – summary of major pathways Noradrenergic neurons Reticulospinal tract Serotonergic neurons Monoaminergic nuclei promote wakefulness via facilitation of the cerebral cortex and inhibition of sleep-promoting neurons (hypothalamus) Coma
Damage to the reticular formation at the level of the rostral pons and caudal medulla may lead to coma or akinetic mutism (coma vigil). An EEG similar to the slow phase of the sleep characterizes this condition, with no appreciable change in the autonomic and somatomotor reflexes or eye movement
Coma might be reversible Brain death
State of irreversible brain damage so severe that normal respiration and cardiovascular function can no longer be maintained
In modern clinical medicine, cessation of life is equated with brain death rather than with cessation of heart beat
Criteria (comatose patients fulfilling these criteria are considered dead)  Unresponsiveness to external stimuli  Absence of spontaneous breathing  Dilated fixed pupils  Absence of brain stem reflexes (corneal, gag, vestibuloocular)  No recognizable reversible cause for the coma  Flat electroencephalogram (absence of electrical activity)  Nonfilling of cerebral vessels in arteriography or radioisotope imaging Reticular formation in medulla Inferior vestibular n. Choraid plexus Accessory cuneate 1 Dorsal moter n. Solitary n. Hypoghossal n. Solitary t. Spinal t. CNY Inferior cerebellar Spinal n. CM ¥ peduncle vp rve t/ NM. ambiguus. Aunterolateral sysberm Medial lemniscus elude oes eeeseeeees ¢Reticular formation Inferior olivary n. Cortico-spinal fibers Hypoglossal nerve (CM XU) —_ = Development of reticular formation Modified from Bayer SA et al. Neurotoxicology 14:83–144, 1993