Acetylcholine is released from the terminals (orange bar) of the preganglionic neurons in the nerve that enters the adrenal glands--there are no postganglionic neurons. The cell bodies of these neurons resides in the spinal cord. When their axons (orange line) leaves the cord they pass through the nearby chain ganglia (light orange circle)--they bypass the cell bodies in those ganglia without synapsing with them. It is technically incorrect to refer to these neurons as 'preganglionic' because there is no ganglion associated with the nerve itself.
The center (i.e., medulla) of the adrenal gland contains chromaffin cells (not shown). These cells contain nicotinic 1 receptors (N1) in their membranes -- color-coded green to indicate that when acetylcholine is attached the cells are activated to secrete (arrows) hormones into the capillaries passing through the gland. The secretion consists of about 80% epinephrine(E) and 20% norepinephrine(NE).
Last update: 9/21/2013