The autonomic nervous system is part of the PNS. It is structurally and functionally composed of two divisions, the sympathetic and parasympathetic divisions. The ANS is characterized by dual innervation which means that the effectors are innervate by both divisions with one countering the other.







Resting and Digesting System


Craniosacral Division (brain stem & sacral region)

Post ganglionic neurons close to target organ


ACh released by both pre and postganglionic cells (cholinergic fibers)


Neurotransmitter effect is always stimulatory







Fight or Flight System


Thoracolumbar System (T1 –L2)


Most Postganglionic fibers release norepinephrine (adrenergic)


Can be stimulatory or inhibitory