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reticular formation.pptx

  1. Reticular formation
  2. Learning objectives  Reticular formation nuclei  Reticular pathways  Physiology of Reticular activating system  Functions of Reticular formation.
  3. Reticular formation  Dense network of neurons and nerve fibers found in Core of brainstem  Indinstinct , not well defined anatomically. 50-80 nuclear masses It can be: Midbrain, Pontine and Medullary RF. Consists of : Aggregates of Neurons Afferent and Efferent connections.
  4. Reticular formation  The neurons have long dendrites and axons.
  5. Reticular formation NUCLEAR COLUMNS: Median column:  Raphe nuclei in midbrain Median Column:  MAGNOCELLULAR  Nucleus gigantocellularis in medulla and pontine tegmental nuclei.
  6. Reticular formation  Lateral columns: PARVOCELLULAR Central nucleus of medulla and pons
  7. Reticular formation  Cardiac centers  Respiratory centers  Vasomotor centers  Salivatory centers  Chemoreceptor neurons.
  8. Reticular formation  They receive afferents from spino-reticular tracts.  Fibers from this part project upwards as Reticular activating system.  Fibers from this part project downwards as medial and lateral reticulospinal tracts.
  9. Reticular pathways Connections of RF:  Afferent connections  Efferent connections: Ascending and Descending projections.
  10. Reticular formation  Afferents: Receives afferents from almost all ascending sensory pathways  Optic pathway  Olfactory pathway  Auditory pathway  Taste pathway  Spinal and Trigeminal pathway  Pain, temperature, vibration and kinesthetic sensation.  Cerebral cortex  Cerebellum  Corpus striatum  Thalmic nuclei
  11. Reticular pathways  Cortico-reticulo-spinal pathways: Cortico-reticulo-cerebellar  Cortico-reticulo-basal ganglia  Visceral control pathways: control of respiration , heart rate and BP  RAS-Reticular activating system.
  12. Reticular pathways  RAS: Also called ARAS from brain stem RF. Polysynaptic pathway Also receives collaterals from:  Spinothalamic tracts  Trigeminal, auditory , visual and olfactory pathway systems.
  13. Reticular pathways  From RAS fibers go to non-specific thalamic nuclei(intralaminar and midline nuclei)  From the thalamus the fibers are projected diffusely and non specifically to whole cortex.  Some fibers bypass the thalamus to project to whole cortex.  RAS is non specific system since it can be stimulated by any sensation from collaterals.  It also receives facilitatory feedback impules from motor cortex and inhibitory feedback impulses from limbic system.
  14. Reticular pathways  Functions of ARAS: Facilitatory to central neurons –increases excitability. Wakefulness and alertness Beta rhythm in ECG. Applied aspects:  Lesions in RAS-Sleep and coma  Benzodiazepines and babituraes prevent synaptic transmission in RAS.
  15. Neurotransmitters of Reticular formation.  Cholinergic neurons : mid brain and pons to cortex  Adrenergic neurons: whole of RF to thalamus to cortex  Nor adrenergic neurons: locus coerulus to cerebellum  Dopaminergic neurons : midbrain RF to basal ganglia  Serotonergic neurons: Raphe nuclei to thalamus, cerebral cortex , thalamus and limbic system From raphe nuclei to spinal cord (control the transmission of pain)
  16. Reticular formation Functions:  Sleep wakefulness: serotonin-secreting neurons in raphe nuclei mediate non-REM sleep  Conditioning and learning: Neural substrate  Selective attention and sensory inattention: FILTER  Control of muscle tone and regulation of postural reflex changes: RF modulates the tone of extensor muscles. Pontine RF has excitatory and Medullary reticulospinal tract has inhibitory influence on extensor muscle tone.
  17. Reticular formation  Autonomic functions: Cortical neurons Through Visceral regulating centers influences the autonomic functions  Modulation of Pain: Raphe nuclei fibers going to spinal cord (substantial gelatinosa) modulate the perception of pain.  Control of neuroendocrine system: control the neuroendocrine system in hypothalamus.