Final answer:
The ANS has two divisions: sympathetic (thoracolumbar) and parasympathetic (craniosacral). Sympathetic nerves pass through sympathetic chain ganglia alongside the vertebral column and affect 'fight or flight' responses. Parasympathetic nerves, which include the vagus nerve, influence 'rest and digest' activities.
Step-by-step explanation:
The autonomic nervous system (ANS) comprises two main divisions: the sympathetic and parasympathetic nervous systems. The sympathetic system, often referred to as the thoracolumbar outflow, has its origins in the thoracic and upper lumbar spinal cord. It is crucial for the 'fight or flight' response, increasing heart rate, dilating the pupils, and redirecting blood flow towards skeletal muscles. The parasympathetic system, or the craniosacral outflow, originates from the brainstem and sacral spinal cord and influences organ systems promoting 'rest and digest' activities, such as slowing the heart rate and stimulating digestion.
The sympathetic nerves emerge from the thoracic and upper lumbar regions and travel through the sympathetic chain ganglia, which run alongside the vertebral column. These ganglia include cervical, thoracic, lumbar, and sacral regions, but only the thoracic and lumbar nerves have direct connections to the spinal cord.
The parasympathetic nerves are associated with the cranial nerves and the sacral spinal cord. Specific cranial nerves, like the vagus nerve (X), carry preganglionic parasympathetic fibers to thoracic and abdominal organs, controlling various body functions such as the diameter of the pupils and digestive processes.