19.3:
Sympathetic Pathways: Sympathetic Chain Ganglia
The sympathetic chains are paired ganglia located bilaterally along the spinal cord.
They are synapse sites between the preganglionic and postganglionic neurons that innervate organs above the diaphragm.
Chain ganglia are divided into the cervical, thoracic, lumbar, sacral, and coccygeal regions.
The neurons in the superior cervical ganglion innervate the head and heart, while the middle and inferior cervical ganglia neurons innervate the heart and blood vessels in the neck, shoulder, and upper limbs.
There are eleven to twelve thoracic ganglia, but synapse occurs only until the fifth thoracic ganglia. Postganglionic neurons from these ganglia innervate the heart, lungs, and bronchi.
The neurons for the head and face exit the ganglia as cephalic periarterial nerves, while those destined for organs in the thoracic cavity, such as the heart and lungs, exit as sympathetic nerves.
The neurons serving the skin of the neck, torso, and limbs leave the ganglia by merging into spinal nerves.
Most of the preganglionic fibers below the thoracic-five region leave the sympathetic chain ganglia without synapsing and travel to the collateral ganglia as splanchnic nerves.
19.3:
Sympathetic Pathways: Sympathetic Chain Ganglia
The sympathetic chain ganglia, also known as the sympathetic trunk ganglia or paravertebral ganglia, are a series of ganglia located bilaterally on either side of the spinal column. These ganglia serve as relay stations for the sympathetic nervous system. Preganglionic neurons originating in the spinal cord project their axons to the sympathetic chain ganglia. Within the ganglia, these preganglionic fibers synapse with postganglionic neurons.
The postganglionic neurons of the sympathetic trunk ganglia follow four pathways that leave the ganglia to innervate their target effector organs.
- Spinal nerves: Some postganglionic axons merge with spinal nerves through the gray rami communicans, providing sympathetic innervation to the skin of the neck, limbs, and torso.
- Cephalic periarterial nerves: Some postganglionic axons wrap around arteries, like the carotid arteries, supplying sympathetic innervation to the face, including sweat glands, blood vessels, hair follicles, and various structures in the head.
- Sympathetic nerves: Some postganglionic axons leave the sympathetic trunk, forming sympathetic nerves that reach visceral effectors in the thoracic cavity, such as the heart and lungs.
- Splanchnic nerves: Some preganglionic fibers pass through the sympathetic trunk without synapsing, forming splanchnic nerves that travel to the collateral ganglia.