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A catecholamine is a monoamine neurotransmitter, an organic compound that has a catechol and a side-chain amine.
The autonomic nervous system (ANS), sometimes called the visceral nervous system and formerly the vegetative nervous system, is a division of the nervous system that operates internal organs, smooth muscle and glands. The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions, such as the heart rate, its force of contraction, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system is the primary mechanism in control of the fight-or-flight response.
The sympathetic nervous system is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.
The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involuntary) functions, ranging from vomiting to sneezing. The medulla contains the cardiovascular center, the respiratory center, vomiting and vasomotor centers, responsible for the autonomic functions of breathing, heart rate and blood pressure as well as the sleep–wake cycle. "Medulla" is from Latin, ‘pith or marrow’. And "oblongata" is from Latin, ‘lengthened or longish or elongated'.
The brainstem is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is continuous with the thalamus of the diencephalon through the tentorial notch, and sometimes the diencephalon is included in the brainstem.
Baroreceptors are sensors located in the carotid sinus and in the aortic arch. They sense the blood pressure and relay the information to the brain, so that a proper blood pressure can be maintained.
The solitary nucleus(SN) (nucleus of the solitary tract, nucleus solitarius, or nucleus tractus solitarii) is a series of neurons whose cell bodies form a roughly vertical column of grey matter in the medulla oblongata of the brainstem. Their axons form the bulk of the enclosed solitary tract. The solitary nucleus can be divided into different parts including dorsomedial, dorsolateral, and ventrolateral subnuclei.
The nucleus ambiguus is a group of large motor neurons, situated deep in the medullary part of the reticular formation named by Jacob Clarke. The nucleus ambiguus contains the cell bodies of neurons that innervate the muscles of the soft palate, pharynx, and larynx which are associated with speech and swallowing. As well as motor neurons, the nucleus ambiguus contains preganglionic parasympathetic neurons which innervate postganglionic parasympathetic neurons in the heart.
Cushing reflex is a physiological nervous system response to increased intracranial pressure (ICP) that results in Cushing's triad of increased blood pressure, irregular breathing, and bradycardia. It is usually seen in the terminal stages of acute head injury and may indicate imminent brain herniation. It can also be seen after the intravenous administration of epinephrine and similar drugs. It was first described in detail by American neurosurgeon Harvey Cushing in 1901.
The baroreflex or baroreceptor reflex is one of the body's homeostatic mechanisms that helps to maintain blood pressure at nearly constant levels. The baroreflex provides a rapid negative feedback loop in which an elevated blood pressure causes the heart rate to decrease. Decreased blood pressure decreases baroreflex activation and causes heart rate to increase and to restore blood pressure levels. Their function is to sense pressure changes by responding to change in the tension of the arterial wall. The baroreflex can begin to act in less than the duration of a cardiac cycle and thus baroreflex adjustments are key factors in dealing with postural hypotension, the tendency for blood pressure to decrease on standing due to gravity.
The reticular formation is a set of interconnected nuclei in the brainstem that spans from the lower end of the medulla oblongata to the upper end of the midbrain. The neurons of the reticular formation make up a complex set of neural networks in the core of the brainstem. The reticular formation is made up of a diffuse net-like formation of reticular nuclei which is not well-defined. It may be seen as being made up of all the interspersed cells in the brainstem between the more compact and named structures.
Alpha (α) motor neurons (also called alpha motoneurons), are large, multipolar lower motor neurons of the brainstem and spinal cord. They innervate extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their contraction. Alpha motor neurons are distinct from gamma motor neurons, which innervate intrafusal muscle fibers of muscle spindles.
The lateral hypothalamus (LH), also called the lateral hypothalamic area (LHA), contains the primary orexinergic nucleus within the hypothalamus that widely projects throughout the nervous system; this system of neurons mediates an array of cognitive and physical processes, such as promoting feeding behavior and arousal, reducing pain perception, and regulating body temperature, digestive functions, and blood pressure, among many others. Clinically significant disorders that involve dysfunctions of the orexinergic projection system include narcolepsy, motility disorders or functional gastrointestinal disorders involving visceral hypersensitivity, and eating disorders.
Central chemoreceptors of the central nervous system, located on the ventrolateral medullary surface in the vicinity of the exit of the 9th and 10th cranial nerves, are sensitive to the pH of their environment.
In mammals, the Bötzinger complex (BötC) is a group of neurons located in the rostral ventrolateral medulla, and ventral respiratory column. In the medulla, this group is located caudally to the facial nucleus and ventral to nucleus ambiguus.
The Bezold–Jarisch reflex involves a variety of cardiovascular and neurological processes which cause hypopnea, hypotension and bradycardia in response to noxious stimuli detected in the cardiac ventricles. The reflex is named after Albert von Bezold and Adolf Jarisch Junior. The significance of the discovery is that it was the first recognition of a chemical (non-mechanical) reflex.
The vasomotor center (VMC) is a portion of the medulla oblongata. Together with the cardiovascular center and respiratory center, it regulates blood pressure. It also has a more minor role in other homeostatic processes. Upon increase in carbon dioxide level at central chemoreceptors, it stimulates the sympathetic system to constrict vessels. This is opposite to carbon dioxide in tissues causing vasodilatation, especially in the brain. Cranial nerves IX and X both feed into the vasomotor centre and are themselves involved in the regulation of blood pressure.
The sympathoadrenal system is a physiological connection between the sympathetic nervous system and the adrenal medulla and is crucial in an organism's physiological response to outside stimuli. When the body receives sensory information, the sympathetic nervous system sends a signal to preganglionic nerve fibers, which activate the adrenal medulla through acetylcholine. Once activated, norepinephrine and epinephrine are released directly into the blood by adrenomedullary cells where they act as the bodily mechanism for "fight-or-flight" responses. Because of this, the sympathoadrenal system plays a large role in maintaining glucose levels, sodium levels, blood pressure, and various other metabolic pathways that couple with bodily responses to the environment. During numerous diseased states, such as hypoglycemia or even stress, the body's metabolic processes are skewed. The sympathoadrenal system works to return the body to homeostasis through the activation or inactivation of the adrenal gland. However, more severe disorders of the sympathoadrenal system such as pheochromocytoma can affect the body's ability to maintain a homeostatic state. In these cases, curative agents such as adrenergic agonists and antagonists are used to modify epinephrine and norepinephrine levels released by the adrenal medulla.
The nucleus paragigantocellularis (nPGi) is a part of the brain, located in the rostral ventral medulla. It is a key brainstem region involved in the expression of cardiovascular and respiratory changes that occur following sympathetic activation. The nPGi is one of two major afferents of the locus coeruleus (LC), and sends collateral projections to the LC and to the nucleus of the solitary tract (NTS). Neurons in this region have also been associated with analgesia processes. Consistent with this, PGi neurons have widespread distributions to brain areas that are important for controlling autonomic activity and nociception.
The ventrolateral medulla, part of the medulla oblongata of the brainstem, plays a major role in regulating arterial blood pressure and breathing. It regulates blood pressure by regulating the activity of the sympathetic nerves that target the heart and peripheral blood vessels.
References
- 1 2 Mischel NA, Subramanian M, Dombrowski MD, Llewellyn-Smith IJ, Mueller PJ (May 2015). "(In)activity-related neuroplasticity in brainstem control of sympathetic outflow: unraveling underlying molecular, cellular, and anatomical mechanisms". Am. J. Physiol. Heart Circ. Physiol. 309 (2): H235–43. doi:10.1152/ajpheart.00929.2014. PMC 4504968 . PMID 25957223.
Specifically, we focus on changes in the rostral ventrolateral medulla (RVLM), a critical brain region for basal and reflex control of sympathetic activity. The RVLM is implicated in elevated sympathetic outflow associated with several cardiovascular diseases including hypertension and heart failure
- ↑ Medullary pressor area: site of action of intravenous physostigmine