The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the nervous system that operates internal organs, smooth muscle and glands. The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions, such as the heart rate, its force of contraction, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system is the primary mechanism in control of the fight-or-flight response.
A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the corresponding cervical, thoracic, lumbar, sacral and coccygeal regions of the spine. There are eight pairs of cervical nerves, twelve pairs of thoracic nerves, five pairs of lumbar nerves, five pairs of sacral nerves, and one pair of coccygeal nerves. The spinal nerves are part of the peripheral nervous system.
The celiac plexus, also known as the solar plexus because of its radiating nerve fibers, is a complex network of nerves located in the abdomen, near where the celiac trunk, superior mesenteric artery, and renal arteries branch from the abdominal aorta. It is behind the stomach and the omental bursa, and in front of the crura of the diaphragm, on the level of the first lumbar vertebra.
The cardiac plexus is a plexus of nerves situated at the base of the heart that innervates the heart.
The sympathetic trunks are a paired bundle of nerve fibers that run from the base of the skull to the coccyx. They are a major component of the sympathetic nervous system.
The abdominal aortic plexus is formed by branches derived, on either side, from the celiac plexus and ganglia, and receives filaments from some of the lumbar ganglia.
Each spinal nerve receives a branch called a gray ramus communicans from the adjacent paravertebral ganglion of the sympathetic trunk. The gray rami communicantes contain postganglionic nerve fibers of the sympathetic nervous system and are composed of largely unmyelinated neurons. This is in contrast to the white rami communicantes, in which heavily myelinated neurons give the rami their white appearance.
The superior hypogastric plexus is a plexus of nerves situated on the vertebral bodies anterior to the bifurcation of the abdominal aorta. It bifurcates to form the left and the right hypogastric nerve. The SHP is the continuation of the abdominal aortic plexus.
The celiac ganglia or coeliac ganglia are two large irregularly shaped masses of nerve tissue in the upper abdomen. Part of the sympathetic subdivision of the autonomic nervous system (ANS), the two celiac ganglia are the largest ganglia in the ANS, and they innervate most of the digestive tract.
The sympathetic ganglia, or paravertebral ganglia, are autonomic ganglia of the sympathetic nervous system. Ganglia are 20,000 to 30,000 afferent and efferent nerve cell bodies that run along on either side of the spinal cord. Afferent nerve cell bodies bring information from the body to the brain and spinal cord, while efferent nerve cell bodies bring information from the brain and spinal cord to the rest of the body. The cell bodies create long sympathetic chains that are on either side of the spinal cord. They also form para- or pre-vertebral ganglia of gross anatomy.
The short ciliary nerves are nerves of the orbit around the eye. They are branches of the ciliary ganglion. They supply parasympathetic and sympathetic nerve fibers to the ciliary muscle, iris, and cornea. Damage to the short ciliary nerve may result in loss of the pupillary light reflex, or mydriasis.
Thoracic splanchnic nerves are splanchnic nerves that arise from the sympathetic trunk in the thorax and travel inferiorly to provide sympathetic supply to the abdomen. The nerves contain preganglionic sympathetic fibers and general visceral afferent fibers.
The aorticorenal ganglion is composed of the superior mesenteric, renal, and inferior mesenteric ganglia. This is distinct from the celiac ganglia. However, they are part of the preaortic ganglia.
The inferior hypogastric plexus is a network of nerves that supplies the organs of the pelvic cavity. The inferior hypogastric plexus gives rise to the prostatic plexus in males and the uterovaginal plexus in females.
Sacral splanchnic nerves are splanchnic nerves that connect the inferior hypogastric plexus to the sympathetic trunk in the pelvis.
The lumbar splanchnic nerves are splanchnic nerves that arise from the lumbar ganglia and travel to an adjacent plexus near the aorta. They originate from L1 and L2. Together with fibres from the aortic plexus, they form the superior hypogastric plexus.
The superior cardiac nerve arises by two or more branches from the superior cervical ganglion, and occasionally receives a filament from the trunk between the first and second cervical ganglia. It runs down the neck behind the common carotid artery, and in front of the Longus colli muscle; and crosses in front of the inferior thyroid artery, and recurrent nerve. The course of the nerves on the two sides then differs.
The lumbar ganglia are paravertebral ganglia located in the inferior portion of the sympathetic trunk. The lumbar portion of the sympathetic trunk typically has 4 lumbar ganglia. The lumbar splanchnic nerves arise from the ganglia here, and contribute sympathetic efferent fibers to the nearby plexuses. The first two lumbar ganglia have both white and gray rami communicates.
The sacral ganglia are paravertebral ganglia of the sympathetic trunk.:39 As the sympathetic trunk heads inferiorly down the sacrum, it turns medially. There are generally four or five sacral ganglia. In addition to gray rami communicantes, the ganglia send off sacral splanchnic nerves to join the inferior hypogastric plexus. Near the coccyx, the right and left sympathetic trunks join to form the ganglion impar.
