Neuroscience/Objectives/Lecture 23
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Objectives: 1–3 - 4 - 5 - 6 - 7 - 8 - 9–10 - 11 - 12 - 13–14 - 15 - 16 - 17 - 18 - 19 - 20 - 21 - 22 - 23 - 24 - 25 - 26
Brainstem reticular formation
Identify the location of the reticular formation in the brainstem.
The reticular formation is present throughout the brainstem, extending from the rostral midbrain to the caudal medulla.
Name the major transmitter of specific neuronal populations located in the reticular formation.
| Neurotransmitter | Neuronal population | Location | Function |
|---|---|---|---|
| Norepinephrine | Ventrolateral cell group | Ventrolateral reticular formation of medulla and pons |
|
| Locus coeruleus (compact: A4, ventral diffuse: A6) | Rostral pons, medial to mesencephalic nucleus and tract |
| |
| Epinephrine | Adrenergic cell groups (C1-C3) | Medulla (level of NTS) |
|
| Dopamine | Substantia nigra (A8-A9) | Pars compacta of substantia nigra |
|
| Ventral tegmental cell group (A10) | Scattered in ventral midbrain between substantia nigra and red nucleus |
| |
| Hypothalamic dopaminergic cell groups (A11-A14) |
|
| |
| Serotonin | Median raphe and dorsal raphe (B8-B9) | Mesencephalon
|
|
| Medullary raphe | Caudal medulla to pons |
| |
| Pontine raphe | Pons |
| |
| Acetylcholine | Mesopontine cholinergic neurons (Ch5, Ch6) | Pontomesencephalic junction
|
|
| Basal forebrain cholinergic neurons | Base of forebrain from medial septal nuclei through diagonal band into substantia innominata and nucleus basalis of Maynert (Ch1-Ch4), ventral to neostriatum |
|
Describe and contrast the functions of the locus coeruleus and dorsal raphe nucleus.
The noradrenergic locus coeruleus regulates sensory input and cortical activation, keeping the individual alert and responsive to unexpected stimuli. The serotonergic dorsal raphe innervates the forebrain and regulates the behavioral state of the nervous system by modulating the responsiveness of cortical neurons.
Whereas the locus coeruleus modifies cortical activity indirectly by regulating sensory input to the cortex, the dorsal raphe directly modulates the responsiveness of cortical neurons in the forebrain.
List the known functions of the major cholinergic cell groups located in the mesopontine tegmentum and basal forebrain area.
Mesopontine tegmentum
- Projects to entire reticular formation
- Projects to thalamus to regulate sleep-wake cycles and to induce cortical arousal during wakefulness and dreaming
Basal forebrain area
- Project to limbic forebrain and neocortex to enhance cortical responses to incoming sensory stimuli
- Degenerate in Alzheimer's disease
Identify the locations of the dopaminergic cell groups in the brainstem and discuss the functions of the mesolimbic, mesocortical, and nigrostriatal dopamine systems.
Dopaminergic neurons of the reticular formation are found in the substantia nigra, ventral tegmental, and hypothalamic cell groups. See above for specific locations.
The pars compacta of the substantia nigra comprises dopaminergic cells that ascend as the nigrostriatal tract and innervate the entire neostriatum. These neurons are important for initiating motor responses.
The mesolimbic and mesocortical cell groups are found in the ventral tegmental cell groups, which are scattered in the ventral mesencephalon between the substantia nigra and red nucleus. They innervate the frontal and temporal cortex as well as limbic regions of the telencephalon, including the amygdala and cingulate cortex. Hence this patwhay is important for regulating emotion (amygdala), thought (forebrain), and memory storage (amygdala).
Describe how specific subgoups of neurons in the brainstem reticular formation regulate cardiac and respiratory functions.
Near the nucleus ambiguus, cells in the rostral ventrolateral medulla (VLM) send fibers to regulate preganglionic sympathetic neurons in the spinal cord. Therefore the rostral VLM directly regulates sympathetic outflow to the heart and vasculature. The rostral VLM itself is regulated by inhibitory neurons in the caudal VLM. Parasympathetic control is mediated by neurons in the nucleus ambiguus and, to a lesser extent, the dorsal motor nucleus of the vagus.
The caudomedial aspect of the solitary nucleus comprises the cardiovascular center which regulates both parasympathetic and sympathetic outflow via projections to the nucleus ambiguus, dorsal motor vagal nucleus (both parasympathetic), and caudal VPM (for sympathetic regulation). GVA input from carotid sinus and aortic arch baroreceptors reaches the cardiorespiratory center in the NTS, producing a negative feedback circuit. When baroreceptor firing increases, the cardiorespiratory center of the NTS increases its outflow to the parasympathetic centers (nucleus ambiguus and dorsal motor vagal nucleus) and sympathetic inhibitory center (caudal VLM), resulting in increased parasympathetic and decreased sympathetic outflow in response to increased blood pressure. [244-246]
Respiration is regulated by the respiratory center, which resides in the ventrolateral medulla, extending from C1 to the level of the facial nucleus. This cell column is divided into a rostral segment, which contains the Bötzinger and pre-Bötzinger complexes, and a caudal segment, the ventral respiratory group (VRG). The VRG projects to the spinal cord and innervates phrenic and thoracic motor neurons that innervate the diaphragm and intercostal muscles, respectively. Rostral VRG neurons drive inspiration, while neurons of the caudal VRG subserve expiration. The Bötzinger complex regulates respiration via inhibitory GABAergic input to the VRG. Rhythmic breathing is established by pacemaker cells in the pre-Bötzinger complex, which comprises the master respiratory center. The VRG receives input from the caudolateral NTS, which receives sensory afferents from chemoreceptors and mechanoreceptors in the carotid body and lungs, respectively.
Understand how neurons in the reticular formation influence sleep and wakeful states.
Reticular activating system
- Pacemakers in locus coeruleus and pontine raphe bathe brain in noepinephrine and serotonin, respectively
- Thalamic reticular nucleus inhibits thalamocortical activity via inhibitory GABAergic fibers
- Mesopontine centers (pedunculopontine and lateral dorsal tegmental nuclei) send inhibitory cholinergic input to the thalamic reticular nucleus; they therefore promote wakefulness
- The tuberomammillary hypothalamic nucleus activates the mesopontine nuclei with histaminergic fibers
- The lateral hypothalamic hypnogenic centers promote sleep by inhibiting the mesopontine and tuberomammillary nuclei via orexigenic fibers
- Ascending fibers travel through mesencephalic reticular formation; damage causes lethargy, stupor, or coma
Sleep cycle
- The locus coeruleus and pontine raphe gradually become less active
- During REM sleep
- Locus coeruleus and pontine raphe are completely inactive
- Mesopontine nuclei are fully active
- Tonic inhibition of limb muscle activity
Define narcolepsy, cataplexy, sleep paralysis, and sleep/night terror disorder.
See glossary.
