A72-year-old man with a history of prostatic cancer comes to the office due to persistent back pain. The patient was recently started on radiation treatment for several vertebral metastases. He has taken acetaminophen and nonsteroidal anti-inflammatory drugs but continues to have severe pain. On physical examination, he has tenderness over several lumbar vertebrae. Neurologic examination is unremarkable. The patient is started on oral morphine therapy. Which of the following is the most likely direct effect of this medication on the spinal cord neurons of this patient?

Question

A72-year-old man with a history of prostatic cancer comes to the office due to persistent back pain.  The patient was recently started on radiation treatment for several vertebral metastases.  He has taken acetaminophen and nonsteroidal anti-inflammatory drugs but continues to have severe pain.  On physical examination, he has tenderness over several lumbar vertebrae.  Neurologic examination is unremarkable.  The patient is started on oral morphine therapy.  Which of the following is the most likely direct effect of this medication on the spinal cord neurons of this patient?

Quizplus · Accepted Answer

Eductional Objective: Opiate analgesics reduce pain by binding to mu receptors and inhibiting synaptic activity in the central nervous system.  Activation of presynaptic mu receptors on the primary afferent neuron leads to closure of voltage-gated calcium channels and reduced excitatory neurotransmitter release.  Binding to mu receptors on the postsynaptic membrane causes opening of potassium channels and membrane hyperpolarization.

A72-Year-Old Man with a History of Prostatic Cancer Comes to the Office