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What is the Reticular Formation ? • Reticular Formation Diffused mass of neurons and nerve fibers forming an ill-defined meshwork of reticulum in the central portion of the brainstem. Various nuclei: 1) Nuclei of medullary reticular formation 2) Nuclei of pontine reticular formation 3) Nuclei of midbrain reticular formation Situated: - Downwards into spinal cord - Upwards up to thalamus and subthalamus Connections of Reticular Formation Fig. 1 -Afferent connections of reticular formation Fig. 2 – Efferent connections of reticular formation Functional divisions of Reticular Formation Ascending Reticular Activating System - ARAS Receives fibers from the sensory pathways via long ascending spinal tracts. Alertness, maintenance of attention and wakefulness. Emotional reactions, important in learning processes. Tumor or lession – sleeping sickness or coma. Fig.3 – Brain section. Reticular Formation Extends throughout brainstem loosely organized neurons, outside of the major nuclear groups of the brainstem. Participate in widespread connections Reticular formation Phylogenetically oldest part of brain Diffuse net-like meshwork (reticulum) Functions: homeostasis, consciousness, arousal, pain, primitive motor control, muscle tone, Vital centers in medulla and pons: cardiovascular, respiratory, homeostatic Ascending reticular activating system (ARAS) originating from midbrain RF: diffuse cortical projections- consciousness, lesions lead to coma Reticular formation 3 ZONE • Raphe nuclei • Medial zone nuclei • Lateral zone nuclei Medial zone Lateral zone Raphe Nuclei Midline - bilaterally Found at all 3 levels of brainstem Neurotransmitter used is serotinin Projections Rostrally - active in sleep program Caudally - modulates pain perception Raphe Nuclei Raphe nuclei of medulla Raphe nuclei of the pontine reticular formation Nucleus raphe obscurus (nucleus raphe obscurus) Nucleus raphe magnus (raphe magnus) Nucleus pallidus (raphe pallidus) Pontine raphe nucleus (raphe pontis) Inferior central nucleus Raphe nuclei of the midbrain reticular formation Superior central nucleus (nucleus centralis superior) Dorsal raphe nucleus (nucleus raphe dorsalis Raphe Nuclei P A I N periaqueductal gray and Raphe nucleus Magnus Stimulation of periaqueductal gray activates Raphe nuclei Outflow to spinal cord, synapses on interneurons in Lamina II (substantia gelatinosa) & III endorphins : regulate pain perception & induce analgesia Descending connections (A) to the dorsal horn, and from there (B) to the periaqueductal grey (PAG). Descending impulses pass (C) to the raphe nuclei, especially the nucleus raphe magnus, in the upper medulla, reticulospinal fibres (D). Central group Central medullary n Gigantocellular n. Oral and caudal Cunieform Subcuniform PPRF Paramedian Pontine Reticular Formation (PPRF) mediate the horizontal eye movements on their ipsilateral sides. innervations from the superior colliculus and from the frontal eye fields via frontopontine fibers. Gigantocellular reticular nucleus giant neuronal cells excites the hypoglossal nucleus, and can play a role in the actions of the said nerve expiration (or outbreathing) along with the parvocellular nucleus 2 1 Lateral reticular nucleus Reticulocerebellar tract and spinal cord Motor systems movement, ocular movement, posture Magnocellular reticular nucleus (lateral ) inspiration (in-breathing) with a part of the ventral r. nucleus (learning / memory?) projections to the vermis of the cerebellum. The rest sends to the hemisphere most input from the spinal cord is relayed into the vermis PMRN : paramedian reticular nucleus Reticulocerebellar tract connections to the spinal cord in a mostly ipsilateral manner projects to the vermis in the anterior lobe, the pyramis and the uvula stereotyped of motion Cholinergic neurons در حرکات کلیشه ای و هوشیاری catecholamine nuclei Locus ceruleus Melanin granules = blue color;( nucleus pigmentosus pontis), Locus ceruleus mediating arousal to be activated by stimuli. modulate pain through pathways that descend to the spinal cord 2.1 Afferent connections from - Spinal cord - Basal ganglia - Cranial nerve nuclei - Cerebral cortex - Cerebellum - Subthalamus, hypothalamus & thalamus 2.2 Efferent connections to - Spinal cord - Basal ganglia - Cranial nerve nuclei - Cerebral cortex - Cerebellum - Subthalamus, hypothalamus & thalamus parvocelular nuclei PVN : parvocellular reticular formation expiration with a part of the gigantocellular nucleus innervate the mesencephalic trigeminal nucleus and the facial, hypoglossal nuclei control feeding reflexes parabrachial nuclei Taste fiber reley kolliker fuse (respiration rhytem regulation Nucleus of Darkschewitz Periaqueductal gray Vertical eye movement Vertical conjugate Gaze Center Rostal interstitial nucleus of MLF Horizontal conjugate Gaze center Interstitial Nucleus of Cajal •ocular movement related to vertical (up or down) eye position and saccades Oculomotor & Trochleai nuclei group of neurons located ventrolateral to the hypoglossal nucleus Basal Forebrain •Stimulating the basal forebrain gives rise to EEG sychrony and sleep. •located near the sub-arachnoidal space. Ach ventral to the lentiform nucleus •Basal Forebrain •includes the septal nuclei and the basal nucleus of Meynert. Cortical ACh release during waking and rapid eye movement (REM) reduced during non-REM (NREM) sleep. Loss of basal forebrain cholinergic neurons : sleep disruption THANK YOU