The ________ NS releases _______ at the nerve endings known as ______ to upregulate cardiac activity.
A. Parasympathetic; Norepi; β1 heart receptors
B. Parasympathetic; No; α 1 heart receptors
C. Sympathetic; Acetylcholine; α1 heart receptors
D. Sympathetic; Norepi; β1 heart receptors
