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[7] [8] Psychological stress increases activation in the sympathetic branch of the autonomic nervous system (ANS) resulting in increased adrenergic input to the spleen via sympathetic nerve fibers descending into lymphoid tissues. [9] [10] The main neural structure responsible for down-regulating psychological stress levels is the prefrontal ...
The sympathetic nervous system's primary process is to stimulate the body's fight or flight response. It is, however, constantly active at a basic level to maintain homeostasis. [4] The sympathetic nervous system is described as being antagonistic to the parasympathetic nervous system.
Examples of sympathomimetic effects include increases in heart rate, force of cardiac contraction, and blood pressure. [1] The primary endogenous agonists of the sympathetic nervous system are the catecholamines (i.e., epinephrine [adrenaline], norepinephrine [noradrenaline], and dopamine ), which function as both neurotransmitters and hormones .
One example is neurons of the sympathetic nervous system (SNS), which release noradrenaline, which, besides affecting postsynaptic receptors, also affects presynaptic α2-adrenergic receptors, inhibiting further release of noradrenaline. [21] This effect is utilized with clonidine to perform inhibitory effects on the SNS.
Many cells have these receptors, and the binding of a catecholamine to the receptor will generally stimulate the sympathetic nervous system (SNS). The SNS is responsible for the fight-or-flight response , which is triggered by experiences such as exercise or fear -causing situations.
The sympathetic nervous system innervates various immunological structures, such as bone marrow and the spleen, allowing for it to regulate immune function. The adrenergic substances released by the sympathetic nervous system can also bind to and influence various immunological cells, further providing a connection between the systems.
Like other components of the sympathetic nervous system, all of these exceptions are still stimulated by cholinergic preganglionic fibers. In both divisions of the autonomic nervous system, postganglionic neurons express nicotinic acetylcholine receptors to receive signals from preganglionic neurons. [2]
Microglial activation in the CNS via purinergic signalling. In the central nervous system (CNS), ATP is released from synaptic terminals and binds to a plethora of ionotropic and metabotropic receptors. It has an excitatory effect on neurones, and acts as a mediator in neuronal–glial communications. [35]