Autonomic Nervous System and its divisions

Autonomic Nervous System 
The autonomic nervous system (ANS) is made up of motor neurons that innervate smooth muscle, cardiac muscle, and glands automatically and usually without the need for conscious intervention. For each impulse there is one auto­nomic ganglion and two motor neurons. The first neuron has a cell body within the central nervous sys­tem and a preganglionic fiber. The second neuron has a cell body within the ganglion and a postganglionic fiber.
The ANS has two divisions: the sympathetic division and the parasympathetic division. Both of these function automatically and usually subcon­sciously in an involuntary manner.
The divisions of the autonomic nervous system: (1) function automatically and usually subconsciously in an involuntary manner. (2) innervate all internal organs. and (3) utilize tvvo motor neurons and one ganglion for each impulse.
Sympathetic Division 
The preganglionic fibers of the sympathetic division arise from the thoracic and lumbar (thoracolumbar) levels of the spinal cord and almost immediately terminate in ganglia that lie near the spinal cord. Thus, in this system, the preganglionic fibers are short, but the postganglionic fibers that make contact with the organs are long.
The sympathetic division is especially important dur­ing emergency situations and is associated with the "fight-or-flight" response. For example, it inhibits the digestive tract, but dilates the pupils, accelerates the heart­beat, and increases the breathing rate. Postganglionic axons release the neurotransmitter norepinephrine (NE).
The sympathetic division brings about the responses associated vvith the "fight-or-flight" response.
Parasympathetic Division 
Cranial nerves, including the vagus nerve, and fibers that arise from the sacral levels of the spinal cord form the parasympathetic division. Therefore, this system is often called the craniosacral portion of the ANS. In the parasympathetic division, the preganglionic fibers are long, and the postganglionic fibers are short because the ganglia lie near or within the organ. The parasympa­thetic division promotes all of the internal responses associated with a relaxed state. For example, it causes the pupils to contract, promotes digestion of food, and retards the heartbeat. The parasympathetic division utilizes the neurotransmitter acetylcholine.
The parasympathetic division brings about the responses associated with normally restful activities.