1. B. Skeletal muscle is innervated by the somatic nervous system. All other choices are tissues that are innervated by the autonomic nervous system.

2. A. Cholinergic fibers do not innervate the ventricular muscles, although there is significant cholinergic innervation to the SA node (B) and the AV node (C). The gastrointestinal tract, including the ileum (E), is extensively innervated by cholinergic fibers, as is the bladder (D).

3. A. Stimulation of the sympathetic noradrenergic neurons to the iris causes contraction of the radial smooth muscle and dilation of the pupil (mydriasis).

4. B. The receptor on skeletal muscle end plate is characterized as a nicotinic receptor. It responds to both nicotine and to acetylcholine. It does not respond to muscarine; that is, it is not a muscarinic receptor.

5. E. aj-Receptors are prominent in smooth muscle of blood vessels; activation of these receptors leads to vasoconstriction. Cardiac acceleration (A) and cardiac contraction (C) are primarily due to pr receptor stimulation. Intestinal relaxation occurs as a result of stimulation of ar and Pi-receptor stimulation.

6. B. Smooth muscle relaxation is primarily under the influence of the sympathetic nervous system. This control is primarily through p2-receptors. pr Receptors are found chiefly in the heart and adipose tissue. ^-Receptors are at postjuctional sites on tissues innervated by adrenergic neurons. a2-Receptors are usually presynaptic, while p3-adreno-ceptors appear to be primarily in adipose tissue.

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