Structure
The Sympathetic Nervous System (SNS) originates from the thoracolumbar region of the spinal cord (T1-L2). Its nerve fibers arise from neurons in the lateral horn of the spinal cord.
Preganglionic neurons: These are shorter neurons that exit the spinal cord and travel to a sympathetic ganglion (a cluster of nerve cell bodies located outside the CNS).
Sympathetic ganglia: These are typically located in two chains called the sympathetic trunk or paravertebral ganglia, running along both sides of the vertebral column. Some ganglia are also located in the abdomen (prevertebral or collateral ganglia).
Postganglionic neurons: These are longer neurons that extend from the ganglia to target organs and tissues.
illustration of the Sympathetic Nervous System structure, with clear indications of the thoracolumbar origin, sympathetic ganglia, and pathways to target organs
(image may contain incorrect data, it is just for illustration purpose)
Neurotransmitters:
The primary neurotransmitter released by preganglionic neurons is acetylcholine (ACh).
The neurotransmitter released by postganglionic neurons is typically norepinephrine (noradrenaline), which acts on adrenergic receptors on target organs.
Functions of Sympathetic Nervous System
The sympathetic nervous system is responsible for the "fight or flight" response, which prepares the body to handle stressful or emergency situations.
Key effects of the sympathetic nervous system include:
Increased heart rate and contractility to pump more blood to muscles and vital organs.
Bronchodilation (expansion of airways) to increase airflow to the lungs.
Pupil dilation (mydriasis) to enhance vision.
Vasoconstriction of blood vessels in the skin and gastrointestinal tract, redirecting blood flow to muscles.
Inhibition of digestive and urinary functions, slowing down processes that are not immediately essential during a crisis.
Release of glucose from the liver into the bloodstream for quick energy.
Sweating to cool the body during increased physical activity.
Ejaculation is stimulated in males as part of the reproductive response.
Adrenal medulla stimulation: This triggers the release of epinephrine (adrenaline) and norepinephrine into the bloodstream, amplifying the effects of the sympathetic system