Reticular formation (RF) in the brain stem, nuclei of RF, RAS, function of RS, coma, brain death

Reticular Formation and its connections 04/10/2016 Dr. Tibor Wenger

Reticular formation: definition Mass of neurons and nerve fibers extending from the medulla (caudal part) to the midbrain (continuing into the zona inserta and reticular nuclei of the diencephalon) Organized into definitive nuclei groups having important afferent and efferent connections

Positions of the reticular formation nuclei (1)

Positions of the nuclei of the reticular formation (2) Reticular nuclei in the caudal region of the pontine tegmentum Reticular nuclei at the level of inferior colliculus

Nuclei of the reticular formation of the brain stem, rostro-caudal orientation

Neurons of the reticular Formation. A: interactions between dendrites and axon collaterals of neurons with asceding (blue) and descending (red) Projections. B: Neuron whose axon divides into long ascending and descending branches (After Barr and Kiernan: The Human Nervous System)

Connections of the central and lateral groups of the reticular nuclei (After Barr and Kiernan: The Human Nervous System)

The afferent connections of the reticular formation Sensory systems: practically most of the sensory system (somatic and visceral) projects upon the RF with exception of medial lemniscus Spinal cord: spinoreticular fibers (mainly from lamina VI-VIII) Cerebral cortex: from wide areas of both motor and sensory cortex (so called: cortico-reticular tract) Cerebellum: projections mainly from nucl. Fastigi Brain stem: lateral hypothalamus, superior colliculus Basal ganglia: pallidum

The efferent connections of the reticular formation 1 Ascending connections Cerebral cortex: few fibers directly, mainly via the diencephalon (thalamus, hypothalamus, subthalamus, particularly intralaminar nuclei (Ascending reticular activating system!) Locus ceruleus (sleep)

The efferent connections of the reticular formation 2 Descending connections: Spinal cord: medial reticulospinal tract, lateral reticulospinal tract Cranial nerve nuclei: practically all nulei of cranial nerves (N. II ?) Local connections: between different groups of RF’s nuclei

Functions of the RF 1 Somatic motor function: both cerebral and cerebellar via cranial nerve nuclei and lamina IX of spinal cord (modification of alpha and gamma motor neurons: pontine facilitatory, the medullary inhibitory influences) Somatic sensory function: selective transmission of sensory impulses pain!

Functions of the RF 2 Visceral motor function: Medial group: Inspiration, depressor effects on circulatory system (hearth rate, blood pressure!) Lateral group: expiration, pressor circulatory effects

Ascending reticular activation system (RAS)

Functions of RAS Brain death: Irreversible brain (in most cases RAS) ACTIVATION:Via diencephalic nuclei major role in arousal and attentiveness, alertness Improuves learning (wakefulness) DESACTIVITY: somnolence (sleep!) coma (not only RF!) Sensitive to general anesthetics and tranquilizing drugs Consciousness in brain degenerative diseases Coma: patient cannot vocalize, has no spontaneous eye movements and no responds reflexlyor no to painful stimuli Brain death: Unresponsivnes to external stimuli, absence of spontaneous breathing, dilated, fixed pupils, flat EEG, no return from coma(no recognizable reversible cause for the coma) Brain death: Irreversible brain (in most cases RAS) damages of respiratory and cardiovascular functions