19.2: Sympathetic Division of the ANS
The sympathetic division of the autonomic nervous system (ANS) plays a crucial role in preparing the body for stress, physical activity, and increased energy demands. This division activates the "fight-or-flight" response, enabling individuals to respond effectively to challenging situations.
Originating in the thoracic and lumbar spinal cord segments, the preganglionic fibers of the sympathetic division exit the spinal cord through the white ramus communicans. They then enter the sympathetic trunk ganglion, where they have three possible locations for synapse with postganglionic fibers: within the sympathetic chain ganglia, at the collateral ganglia, or in the adrenal medulla.
Sympathetic Chain Ganglia
The sympathetic chain ganglia, also known as the paravertebral ganglia, are a series of interconnected ganglia positioned bilaterally along the spinal cord. These ganglia form a chain-like structure that runs parallel to the vertebral column. The sympathetic chain ganglia play a crucial role in regulating various physiological functions throughout the body.
Collateral Ganglia
The collateral ganglia, also known as the prevertebral or preaortic ganglia, are positioned anteriorly to the spinal cord. Once within the collateral ganglia, the preganglionic fibers synapse with the postganglionic fibers. These postganglionic fibers extend from the ganglia and innervate specific target organs in the abdominal and pelvic regions. Organs innervated by the collateral ganglia include the heart, lungs, liver, stomach, intestines, and kidneys. The ganglia are involved in the control of functions such as cardiac activity, bronchial dilation, gastrointestinal motility, and urinary system regulation.
Adrenal Medulla
The adrenal medulla, found within the adrenal gland, plays a unique role in the sympathetic division. When stimulated, it releases neurotransmitters such as adrenaline and noradrenaline into the bloodstream. These neurotransmitters act as hormones and regulate the activity of distant cells, further enhancing the body's response to stress and physical demands.
