The autonomic nervous system, composed of the sympathetic and parasympathetic divisions, controls and regulates the more autonomic functions of the body, such as involuntary muscle movements, breathing rate and dilation or constriction of the blood vessels. When attempting to understand the autonomic nervous system, there are certain anatomical structures that must be first understood.
Structures of the sympathetic division
The sympathetic division of the autonomic nervous system is responsible for the body’s autonomic functions that are more “alert” or require more energy. Some examples include increased heart rate and blood pressure, or increased respiration.
The sympathetic division of the autonomic nervous system is often referred to as the thoracolumbar division due to the ganglionic fibers of the sympathetic division protruding from the spine in both the thoracic and lumbar regions, converging with the sympathetic chain of ganglia, also known as the paravertebral ganglia. The sympathetic chain is composed of a chain of ganglion, located on both sides of the spinal column along the entire spine, despite originating from only the cervical and lumbar regions.
Each ganglion located within the chain is joined to a spinal nerve by a structure known as the communicating rami. Much like the matter of the brain and spinal cord, there is a white communicating ramus and a gray communicating ramus. The nerve fibers exit the chain through one of three ways; returning to the spinal nerves, converging with sympathetic nerves to innervate structures such as the arteries, or glands, or they contribute to a second chain of ganglia known as the collateral ganglia or prevertebral ganglia.
Structures of the parasympathetic division
The parasympathetic division of the autonomic nervous system is related to the regulation of the calmer functions of the autonomic nervous system, such as rest, digestion and excretion. The parasympathetic division of the autonomic nervous system is also known as the craniosacral division, as its fibers are contained within certain nerves of the cranium and sacrum. The fibers of the parasympathetic division of the autonomic nervous system exit the brainstem along some of the cranial nerves; the oculomotor nerve, the facial nerve, the glossopharyngeal nerve, and the vagus nerve.
Other structures
Other structures that function within the autonomic nervous system include the adrenal glands, the centralized nervous system unique to the digestive system known as the enteric nervous system and is composed of thousands of neurons lining the intestinal tract.
References
Saladin, K. S. (2010). Anatomy & physiology: the unity of form and function (5th ed.). New York: McGraw-Hill.
More on the nervous system
Subdivisions of the Nervous System
The Structure and Function of Neurons in the Nervous System
Understanding Nervous Tissue