Reticular Activating System

1. Reticular Activating System

2. Direct Continuousstimulation from lower brain Intralaminar Nuclei of thalamus By PET (Positron emission tomography) Scan

3. Activating-Driving systems of the Brain • Continuous stimulation from lower brain • Direct stimulation • By activating Neurohormonal system

4. Excitation (Acetylcholine) Bulboreticular facilitatory area (Reticular Excitatory area ) In reticular substance of the pons and mesecephalon Excitatory signals to 1. cerebral cortex through Thalamus (Mainly) direct 2. Spinal cord (Antigravity muscles) Itself receives excitatory signals from Cerebral cortex (Positive feedback Spinal cord (e.g. pain) Direct Continuousstimulation from lower brain

5. Direct Continuousinhibition from lower brain • Inhibition (Serotonin) • Reticular inhibitory area • In medulla • Inhibitory signals to Reticular Excitatory area

6. Significance of Thalamus • Almost all areas of cerebral cortex connects with its own highly specific area in the thalamus • Signals regularly reverberate between cerebral cortex and thalamus

7. Areas of cerebral cortex that connect with specific portions of thalamus To and fro connections Thalamo- Cortical system

8. Activating-Driving systems of the Brain. Continuous stimulation from lower brain.Mainly through Thalamus

9. Continuous stimulation from lower brain by activating Neurohormonal system • Hours or minutes • FOUR Neurohormonal systems

10. Continuous stimulation from lower brain byFOUR Neurohormonal systems 1.The locus ceruleus and the norepinephrine system • Located at juncture between pons and mesencephalon post • Mainly Excitatory • Dreaming • REM sleep

12. Continuous stimulation from lower brain by ;FOUR Neurohormonal systems 2. The substantia nigra and the dopamine system • Located in superior mesencephalon ant • its neurons send nerve endings mainly to the caudate nucleus and putamen of the cerebrum • send their endings into more ventral areas of the brain-- hypothalamus and the limbic system. • Mainly inhibitory

13. Continuous stimulation from lower brain by ;FOUR Neurohormonal systems 3. The raphe nuclei and the serotonin system • Thin nuclei located in midline in pons and medulla • send fibers • into the diencephalon • to the cerebral cortex(few) • to the spinal cord—serotonin suppress pain • Mainly inhibitory • Normal sleep

15. Continuous stimulation from lower brain by ;FOUR Neurohormonal systems 4. The gigantocellular neurons of the reticular excitatory area and the acetylcholine system • In the reticular excitatory area of pons and mesencephalon • The fibers divide immediately into two branches • to the brain • through the reticulospinal tracts into the spinal cord--acetylcholine. • Mainly Excitatory---acutely awake and excited nervous system

16. Summary of the Activating-Driving systems of the Brain Continuous stimulation from lower brain • Direct stimulation Excitation (Acetylcholine) Reticular Excitatory area Inhibition (Serotonin) Reticular inhibitory area 2. By activating Neurohormonal system • FOUR Neurohormonal systems • Located in pons ,mesencephalon and medulla • norepinephrine system (Mainly Excitatory) • dopamine system (Mainly inhibitory) • Serotonin system (Mainly inhibitory) • Acetylcholine system (Mainly Excitatory) Mainly through Thalamus

17. Significance of continuous excitation • If all sensory inputs blocked • →cerebral activity greatly reduced • → coma

18. Other Neurotransmitters and Neurohormonal Substances Secreted in the Brain • Enkephalins, gamma-aminobutyric acid, glutamate, vasopressin • adrenocorticotropic hormone, α-melanocyte stimulating hormone (α-MSH), neuropeptide-Y (NPY), • epinephrine, histamine, endorphins, angiotensin II, and neurotensin

19. Continuous stimulation from lower brain by activating Neurohormonal system

20. 1. The gigantocellular neurons of the reticular formation release which neurotransmitter? A) Norepinephrine B) Serotonin C) Dopamine D) Acetylcholine E) Glutamate

21. 2. Neurons located in which area release serotonin as their neurotransmitter A) Periaqueductal gray area B) Interneurons of the spinal cord C) Periventricular area D) Nucleus raphe magnus

22. 3. Which neurotransmitter is used by the axons of locus ceruleus neurons that distribute throughout much of the brain A) Norepinephrine B) Dopamine C) Serotonin D) Acetylcholine

23. Sleep

24. Sleep Definition: an unconsciousness from which the person can be aroused Types:- 1.Non REM Sleep 2. REM sleep 1. Non REM (slow wave sleep)  75 % Characteristics: • Deep restful • 4 stages • EEG: High amplitude , low frequency slow waves • Dreamless sleep • Decrease vegetative functions 10—30% decrease in B.P, R.R, B.M.R, Peripheral Vascular Tone

25. Sleep 2. REM Sleep ( Paradoxical, Desynchronized) • 5 – 30 min • Every 90 min • Duration decrease with deep sleep Characteristics: • Active dreaming • Difficult to arouse (morning) • Decrease muscle tone • Heart Rate, Resp .Rate are irregular • Few irregular muscles movements (eyes) • Active brain • EEG: Rapid, low voltage

26. EEG during different stages of wakefulness and sleep

27. Alert wakefulness is characterized by high-frequency beta waves • quiet wakefulness is usually associated with alpha waves

28. Slow-wave sleep is divided into 4 stages • Iststage, -the voltage of the EEG waves becomes low broken by short spindle-shaped bursts of alpha waves that occur periodically

29. Stages 2, 3, and 4 • frequency of the EEG becomes progressively slower until it reaches a frequency of only one to three waves per second in stage 4 (delta waves)

30. REM sleep • waves are irregular and of high frequency-- desynchronized nervous activity as found in the awake state • called desynchronized sleep because there is lack of synchrony in the firing of the neurons despite significant brain activity

31. Stages of sleep

33. Alpha waves • frequency between 8 and 13 cycles/sec – • healthy adults when they are awake and in a quiet, resting state of cerebration • voltage is usually about 50 microvolts • disappear during deep sleep

34. Beta waves • frequency greater than 14 cycles/ sec-- 80 cycles/sec • awake alert eyes open --specific type of mental activity the alpha waves are replaced by asynchronous, higher frequency but lower voltage beta waves

35. Theta waves • have frequencies between 4—7 cycles/sec • occur normally in children • during emotional stress in some adults (disappointment and frustration) • in many brain disorders(degenerative brain states)

36. Delta waves • frequencies less than 3.5 cycles/sec • voltages two to four times greater than most other types of brain waves • very deep sleep • in infancy • serious organic brain disease • delta waves can occur strictly in the cortex independent of activities in lower regions of the brain

37. Basic Theories • Passive theory (reticular activating system became fatigued) • Active inhibitory process (sleep is caused by an active inhibitory process-- transecting the brain stem at the level of the midpons creates a brain cortex that never goes to sleep)--a center below the midpontile level reqd for sleep)

38. Genesis of Sleep Stimulation of synchronizing regions: 1. Basal fore-brain sleep zone: • Raphe nuclei in lower half of pons and medulla • Serotonin Contd…

39. 2. Medullary synchronizing zone: • Stimulation of nucleus tractus solitarius of brain stem can also cause sleep • This nucleus is the termination in the medulla and pons for visceral sensory signals entering by way of the vagus and glossopharyngeal nerves.

40. Genesis of Sleep • 3. Diencephalic sleep zone: Stimulation of several regions as • the rostral part of the hypothalamus, mainly in the suprachiasmalarea (2) in the diffuse nuclei of the thalamus .

41. Lesions in Sleep-Promoting Centers Can Cause Intense Wakefulness • lesions in the raphe nuclei • lesions in the medial rostral suprachiasmal area in the anterior hypothalamus

42. Neurotransmitters • Sleep peptide • Serotonin • Muramyl peptide • Adenosine

43. Genesis of REM Sleep • Large Acetylcholine secreting neurons in upper brainstem reticular formation • via efferent fibers, activate many portions of the brain

44. If sleep centers are not activated Cycle Between Sleep and Wakefulness mesencephalic and upper pontile reticular activating nuclei are released from inhibition- reticular activating nuclei become spontaneously active. cerebral cortex and the peripheral nervous system excited ---send positive feed back signals to reticular activating nuclei wakefulness sustains

45. Sleep Wake Cycle • after the brain remains activated for many hours, even the neurons in the activating system become fatigued. • the positive feedback cycle between the mesencephalic reticular nuclei and the cerebral cortex fades and the sleep promoting effects of the sleep centers take over • leading to rapid transition from wakefulness back to sleep.

46. Physiological Effects • restores both normal levels of brain activity and normal “balance” among the different functions of the central nervous system Sleep Disorders: • Insomnia • Fatal familial insomnia • Somnambulism • Narcolepsy • Sleep apnea

47. Effect of varying degrees of cerebral activity on the basic rhythm of the electroencephalogram

48. Effect of Varying Levels of Cerebral Activity on the Frequency of the EEG • the average frequency increases progressively with higher degrees of activity • delta waves in surgical anesthesia and deep sleep • theta waves in psychomotor states • alpha waves during relaxed states • beta waves during intense mental activity or fright (asynchronous)

49. MCQ Regarding induction of normal sleep , which of the following Neurotransmitter is plays an important role A) Acetyl Choline B) Dopamine C) Glutamate D) Serotonin

50. Regarding EEG, which waves predominate in a person who is sitting in a relaxed state with closed eyes • Alpha waves • Beta waves • Theta waves • Delta waves