Question

describe the physiological functions of sympathetic neurons

Answer 1

The sympathetic nervous system (SNS) is one of the two main divisions of the autonomic nervous system

The sympathetic nervous system's primary process is to stimulate the body's fight-flight-or-freeze response. It is, however, constantly active at a basic level to maintain homeostasis homeodynamics.

There are two kinds of neurons involved in the transmission of any signal through the sympathetic system: pre-ganglionic and post-ganglionic.

The shorter preganglionic neurons originate in the thoracolumbar division of the spinal cord specifically at T1 to L2~L3, and travel to a ganglion, often one of the paravertebral ganglia, where they synapse with a postganglionic neuron. From there, the long postganglionic neurons extend across most of the body.

At the synapses within the ganglia, preganglionic neurons release acetylcholine, a neurotransmitter that activates nicotinic acetylcholine receptors on postganglionic neurons. In response to this stimulus, the postganglionic neurons release norepinephrine, which activates adrenergic receptors that are present on the peripheral target tissues. The activation of target tissue receptors causes the effects associated with the sympathetic system.

The sympathetic nervous system is responsible for up- and down-regulating many homeostatic mechanisms in living organisms. Fibers from the SNS innervate tissues in almost every organ system, providing at least some regulation of functions as diverse as pupil diameter, gut motility, and urinary system output and function.

It is perhaps best known for mediating the neuronal and hormonal stress response commonly known as the fight-or-flight response. This response is also known as sympatho-adrenal response of the body, as the preganglionic sympathetic fibers that end in the adrenal medulla (but also all other sympathetic fibers) secrete acetylcholine, which activates the great secretion of adrenaline (epinephrine) and to a lesser extent noradrenaline (norepinephrine) from it. Therefore, this response that acts primarily on the cardiovascular system is mediated directly via impulses transmitted through the sympathetic nervous system and indirectly via catecholamines secreted from the adrenal medulla.

The sympathetic nervous system is responsible for priming the body for action, particularly in situations threatening survival.One example of this priming is in the moments before waking, in which sympathetic outflow spontaneously increases in preparation for action.

Sympathetic nervous system stimulation causes vasoconstriction of most blood vessels, including many of those in the skin, the digestive tract, and the kidneys. This occurs as a result of activation of alpha-1 adrenergic receptors by norepinephrine released by post-ganglionic sympathetic neurons.

Examples of sympathetic system action on various organs:

Eye	Dilates
Heart	Increases rate and force of contraction
Lungs	Dilates bronchioles
Blood vessels	Dilate in skeletal muscle
Digestive system	Constrict in gastrointestinal organs
Sweat glands	Activates sweat secretion
Digestive tract	Inhibits peristalsis
Kidney	Increases renin secretion
Ductus deferens	Promotes emission prior to ejaculation