reticular formation.pptx

Reticular formation

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.