Cns 14

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Cns 14

  1. 1. The Reticular Formation <ul><li>The reticular formation extends through the central core of the medulla oblongata, pons, and midbrain. </li></ul><ul><li>It is an intricate system composed of loosely clustered neurons in what is otherwise white matter </li></ul>
  2. 2. The Reticular Formation <ul><li>Reticular neurons can be localized into three broad columns along the length of the brain stem </li></ul><ul><ul><li>Raphe </li></ul></ul><ul><ul><li>Medial nuclear (large cell) group </li></ul></ul><ul><ul><li>Lateral nuclear (small cell) group </li></ul></ul>
  3. 3. The Reticular Formation <ul><li>The outstanding feature of the reticular neurons is their far-flung axonal connections </li></ul><ul><li>Individual reticular neurons project to the thalamus, cerebellum, and spinal cord </li></ul><ul><li>Widespread connections make reticular neurons ideal for governing the arousal of the brain as a whole </li></ul>
  4. 4. The Reticular Formation <ul><li>Certain reticular neurons send a continuous stream of impulses to the cerebrum (through relays in the thalamus) thereby maintaining the cerebral cortex in an alert state </li></ul><ul><li>This arm of the reticular formation is called the reticular activating system (RAS) or Ascending reticular formation </li></ul>
  5. 5. I The Reticular Activating System (Ascending reticular system) <ul><li>The RAS synapses with all major ascending sensory tracts enhancing arousal of the cerebrum </li></ul><ul><li>The RAS functions in arousal from sleep </li></ul><ul><li>It can be affected by general anesthesia, alcohol, tranquilizers, and sleep inducing drugs </li></ul><ul><li>Head trauma can also lead to loss of consciousness </li></ul>
  6. 6. Reticular Formation <ul><li>The RAS also acts as a filter to dampen repetitive, familiar, or weak signals </li></ul><ul><li>It is estimated that 99% of all sensory stimuli is disregarded as unimportant </li></ul>
  7. 7. The Reticular Activating System <ul><li>The activity of the RAS is inhibited by sleep centers in the hypothalamus and other neural regions </li></ul><ul><li>Damage to the RAS limits arousal and can result in coma </li></ul>
  8. 8. II Descending Reticular Formation <ul><li>The reticular formation also has a motor component </li></ul><ul><li>Some if its motor nuclei project to motor neurons in the spinal cord via the reticulospinal tracts </li></ul><ul><li>These help control the skeletal muscles during coarse movements of the limbs </li></ul><ul><li>Other reticular motor nuclei are autonomic centers that regular visceral motor functions (heart rate & respiration) </li></ul>
  9. 9. Areas in the brain where stimulation produces facilitation (+) or inhibition (-) of stretch reflexes . 1. motor cortex; 2. Basal ganglia; 3. Cerebellum; 4. Reticular inhibitory area; 5. Reticular facilitated area; 6. Vestibular nuclei. Facilitated and inhibitory area
  10. 10. 1. Facilitated area—roles of the reticular and vestibular nuclei. : A. The pontine reticular nuclei  Located slightly posteriorly and laterally in the pons and extending to the mesencephalon,  Transmit excitatory signals downward into the cord (the pontine reticulospinal tract) <ul><li>motor cortex; </li></ul><ul><li>2. Basal ganglia; </li></ul><ul><li>3. Cerebellum; </li></ul><ul><li>4. Reticular inhibitory area; </li></ul><ul><li>5. Reticular facilitated area; </li></ul><ul><li>6. Vestibular nuclei . </li></ul>
  11. 12. B . The vestibular nuclei  selectively control the excitatory signals to the different antigravity muscles to maintain equilibrium in response to signals from the vestibular apparatus. <ul><li>motor cortex; </li></ul><ul><li>2. Basal ganglia; </li></ul><ul><li>3. Cerebellum; </li></ul><ul><li>4. Reticular inhibitory area; </li></ul><ul><li>5. Reticular facilitated area; </li></ul><ul><li>6. Vestibular nuclei . </li></ul>
  12. 13. MOTOR CORTEX MOTOR TRACTS & LOWER MOTOR NEURON SKELETAL MUSCLE MIDBRAIN & RED NUCLEUS (Rubrospinal Tract) PONS & MEDULLA RETICULAR FORMATION (Reticulospinal Tracts) VESTIBULAR NUCLEI (Vestibulospinal Tract) LOWER (ALPHA) MOTOR NEURON THE FINAL COMMON PATHWAY UPPER MOTOR NEURON (Corticospinal Tracts)
  13. 14.  Terminate on the motor neurons that exciting antigravity M. of the body (the M. of vertebral column and the extensor M. of the limbs).  Have a high degree of natural (spontaneous) excitability .  Receive especially strong excitatory signals from vestibular nuclei and the deep nuclei of the cerebellum.  Cause powerful excitation of the antigravity M throughout the body (facilitate a standing position), supporting the body against gravity. 1. motor cortex; 2. Basal ganglia; 3. Cerebellum; 4. Reticular inhibitory area; 5. Reticular facilitated area; 6. Vestibular nuclei. Properties of the Facilitated Area
  14. 15. 2. Inhibitory area –Medullary reticular system - Extend the entire extent to the medulla, lying ventrally and medially near the middle. - Transmit inhibitory signals to the same antigravity anterior motor neurons (medullary reticulospinal tract). 1. motor cortex; 2. Basal ganglia; 3. Cerebellum; 4. Reticular inhibitory area; 5. Reticular facilitated area; 6. Vestibular nuclei.
  15. 16. MOTOR CORTEX MOTOR TRACTS & LOWER MOTOR NEURON SKELETAL MUSCLE MIDBRAIN & RED NUCLEUS (Rubrospinal Tract) PONS & MEDULLA RETICULAR FORMATION (Reticulospinal Tracts) VESTIBULAR NUCLEI (Vestibulospinal Tract) LOWER (ALPHA) MOTOR NEURON THE FINAL COMMON PATHWAY UPPER MOTOR NEURON (Corticospinal Tracts)
  16. 17. - Receive collaterals from the corticospinal tract; the rubrospinal tracts; and other motor pathways. These collaterals activate the medullary reticular inhibitory system to balance the excitatory signals from the P.R.S., so that under normal conditions, the body muscles are normally tense. 1. motor cortex; 2. Basal ganglia; 3. Cerebellum; 4. Reticular inhibitory area; 5. Reticular facilitated area; 6. Vestibular nuclei.
  17. 18. <ul><li>Decerebrate Rigidity: Transection of the brainstem at midbrain level (above vestibular nuclei and below red nucleus) </li></ul><ul><li>Symptoms include: </li></ul><ul><ul><li>extensor rigidity or posturing in both upper and lower limbs </li></ul></ul>Decerebrate Rigidity
  18. 19. <ul><li>Results from: </li></ul><ul><ul><li>loss of input from inhibitory medullary RF (activity of this center is dependent on input from higher centers). </li></ul></ul><ul><ul><li>active facilitation from pontine RF (intrinsically active, and receives afferent input from spinal cord). </li></ul></ul>
  19. 20. <ul><li>The extensor rigidity is  -loop dependent </li></ul><ul><ul><li>section the dorsal roots interrupts the  -loop, and the rigidity is relieved. This is  -rigidity. </li></ul></ul>THE  -LOOP?  MUSCLE Muscle spindle Activation of the  -loop results in increased muscle tone  1a Descending influence (UMN)
  20. 21. Reticular Formation Function <ul><li>Arousal </li></ul><ul><li>Tonal Modulation </li></ul><ul><li>Pain Processing </li></ul><ul><li>Regulation of </li></ul><ul><ul><li>Vomiting </li></ul></ul><ul><ul><li>Coughing </li></ul></ul><ul><ul><li>Cardiovascular Functions </li></ul></ul><ul><ul><li>Respiration </li></ul></ul><ul><ul><li>Speech Functions </li></ul></ul>

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