Which of these is not used by the nervous system to instruct the endocrine systema. neurotransmittersb. exocrine glandsc. action potentialsd. neuroendocrine cells

The correct answer is B.exocrine glands.
It is because exocrine glands do not belong to the neuroendocrine system. The neuroendocrine system integrates the interaction between the nervous system and the endocrine system to regulate the physiological processes of the human body (homeostasis, reproduction, metabolism, osmolarity, energy regulation,  blood pressure). The major systems within neuroendocrinology systems are hypothalamic–pituitary–adrenal axis, hypothalamic–pituitary–thyroid axis,hypothalamic–pituitary–gonadal axis.