3 Reticular formation (RF) RF is a set of interconnected nuclei that are located throughout the brain stemOne of the phylogenetically oldest portions of the brainLocal projectionsLocal-circuit interneuronsReflexive and stereotyped behaviors involving face and head:Chewing, swallowing and vomitingRespiratory activities (coughing, hiccups and sneezing)Cardiovascular responsesLong projection systemsAscending to cortexDescending to spinal cordFunctions of long projectionsPain/ sensory perceptionPostureWakefulness/ arousalFiltering incoming stimuli to discriminate irrelevant background stimuliBrain stem
4 Reticular formation (RF) The ascending reticular formation (the reticular activating system)Responsible for the sleep-wake cycleMediates various levels of alertness and consciousness.Projects to the mid-line group of the thalamus, which also plays a role in wakefulness. From there, information is sent to the cortex.The descending reticular formation Involved in posture and equilibrium as well as autonomic nervous system activity.Involved in sensory and motor modulation.It receives information from the hypothalamus.
5 RF subsystems Six neurotransmitter systems Choline (Ch)/ Acetylcholine Norepinephrine / noradrenaline (A)Medulla: A1,A2Pons: A5, A6, A7Epinephrine / Adrenaline (C)Medulla: C1,C2Dopamine (A8-A17)Serotonin (B)Medulla (B1-B3)Pons and midbrain (B4-B8)Choline (Ch)/ AcetylcholineHistamine (E)(A)(B)
6 Noradrenergic/ adrenergic neurons in medulla DorsalVentralA1/ C1: near nucleus ambiguus; A2/ C2: Nucleus of the solitary tract/ dorsal motor vagal nucleus; LC (A6): Locus ceruleusA1/ A2 groups project to hypothalamus and controls cardiovascular and endocrine functionsA5/A7 are located in the pons and mainly projects to the brain stem and spinal cord where they modulate autonomic reflexes and painC1 neurons projects to hypothalamus where they modulate cardiovascular and endocrine functionsC1 neurons also projects to the spinal cord where they provide tonic excitatory input to vasomotor neuronsC2 neurons projects to the parabrachial nucleus providing visceral input
7 Noradrenergic (NA) cell groups Locus ceruleusLocated in the dorsal wall of the rostral ponsContains the largest collection of NA cellsConsists of ~ neuronsProjects to every major region of the brain and spinal cordMaintains vigilance and responsiveness to novel/ unexpected stimuliInfluences arousal including sensory perception and muscle toneIs involved in physiological stress responses
8 Dopaminergic cell groups Hypothalamic DA neuronsSN and VTA DA neuronsLargest DA groups of neuronsSubstantia nigra (A8, A9)Ventral tegmental area (A10)Other:Dorsal hypothalamus (A11, A13) => spinal cordTuberoinfundibular hypothalamic neuroendocrine system (A12, A14)Olfactory tubercke (A15) and bulb (A16)Retina (A17)Ascending input to the cerebral cortex and the basal gangliaNigrostriatal pathway (Globus pallidus, Thalamus)Mesocortical pathway (Prefrontal cortex, ACC)Mesolimbic pathway (Nac, Hipp)FunctionsInitiation of motor responsesEmotions, thought and memoryReward system/ reinforcement (drug addiction)Regulation of sympathetic preganglionic neuronsEendocrine control
9 Serotonergic cell groups The raphe nuclei (RN)Upper/ rostral RN in pons and midbrainRaphe pontis (B4-B6)Median raphe (B8)Dorsal raphe (B7)Lower/ posterior RN in medullaRaphe magnus (B1)Raphe pallidus (B2)Raphe obscurus (B3)Projections of RNRostral RN projects to forebrainPosterior RN projects to the brain stem and spinal cordFunctions of the rostral RNRegulation of the sleep-wake cycleAffective behaviorFunctions of the posterior RNRegulation of motor tone and pain
10 Cholinergic cell groups Ch is used by both somatic and autonomic motor neuronsLoci in midbrainPedunculopontine nucleus (PPT), Ch6Laterodorsal tegmental nucleus (LDT), Ch5ProjectionsReticular formationThalamusLateral hypothalamusFunctionsCortical arousal during wakefulness and dreaming (ascending arousal system)Regulation of sleep-wake cycleEnhancement of incoming sensory stimuliAscending arousal system
11 Histaminegic cell groups All histaminergic neurons are located in the posterior hypothalamusTuberomammillary nucleus (TMN)VentrolaterallyDorsomediallyProjects to all major parts of cerebral cortex and spinal cordFunctionsRegulation of behavioral arousalRegulation of sleepCircadian rhythm
12 Reticular formation (RF): again RF is a set of interconnected nuclei that are located throughout the brain stemLocal projectionsLocal-circuit interneuronsReflexive and stereotyped behaviors involving face and head:Chewing, swallowing and vomitingRespiratory activities (coughing, hiccups and sneezing)Cardiovascular responsesLong projection systemsAscending to cortexDescending to spinal cordFunctions of long projectionsPain/ sensory perceptionPostureWakefulness/ arousalFiltering incoming stimuli to discriminate irrelevant background stimuliBrain stem
13 Descending projections Pain modulationSpinal dorsal hornRaphe magnus (serotonergic) in rostral medulla<= opiodergic periaqueductal greyNoradrenergic neurons in ponsFunction: descending inhibition of nociceptive transmissionPosture, gait and muscle tone modulationMedial reticulospinal tractsOrigins from pontine reticular formationFunction: facilitation of spinal motor neurons in legs for postural support and patterned stereotyped movementsLateral reticulospinal tractsOrigins from medial medullary reticular formationFunction: inhibits cranial and spinal motor neurons => motor tone
14 Ascending arousal system Two ascending branchesThalamusLateral hypothalamusMultiple neurotransmitter systemsFunctions:Increased arousal: wakefullness and vigilanceIncreased neuronal responses to sensory stimuliLesionsDisruption impairs consciousness
15 Electroencephalography ConsciousnessBeing aware of oneself and one’s place in the enviromentThe ability to respond/ orient appropriately to environmental stimuliIt is not sufficient to say that consciousness result from the summed cortical activity since the brain stem is crucialTransection of the brain stem below the level of the rostral pons does not affect consciousnessAcute transection rostral to inferior colliculus result in coma (unarousability)EEG is important in assessment of wakefulnessReflects firing patterns in the thalamocortical pathway (transmission and burst mode)Wakefulness: low voltage, high frequency, desynchronized patternsComa: high voltage , low frequency, synchronized patterns as in sleepBurst mode: hyperpolarized neurons respond to brief depolarization with bursts
17 Integration of sensory input and motor output occurs in the brain stem as well. For example, the midbrain integrates auditory input and motor responses in the eye.The brain stem also contains specific pathways which move information from the spinal level up to the brain and other descending pathways from the brain.