Autonomic Nervous Systems
We administer hexamethonium to a subject. He is in the supine position. Which of the following responses would you expect in response to this drug?
|B||Increased GI tract motility, possible spontaneous defecation|
|C||Increased salivary secretions|
a. Hexamethonium is an autonomic ganglionic blocking drug. So by blocking neurotransmission across all autonomic ganglia (and activation of the adrenal medulla), we essentially denervate distal structures. Now we observe how things change.
b. For the structures and functions listed, it is the parasympathetic nervous system that exerts the predominant resting tone. Only control of vascular smooth muscle tone (and, therefore, of blood pressure) is primarily regulated by the sympathetic nervous system.
c. Block the ganglia and vasodilation will occur as predominant SNS influences are removed. As far as the other structures go—all of which are mainly influenced by the PNS at rest—we would observe a rise of heart rate, decreases of bladder and gut tone (e.g. reduced tone of the bladder detrusor and longitudinal muscles of the gut), mydriasis, and reduced salivary secretions (xerostomia). Sweat gland secretions, which also have predominant sympathetic control, would decrease too.