True regarding morphine –
**Core Concept**
Morphine is a potent opioid analgesic that acts on the central nervous system to produce analgesia, euphoria, and respiratory depression. Its effects are mediated through binding to opioid receptors in the brain and spinal cord.
**Why the Correct Answer is Right**
Morphine exerts its analgesic effects by activating μ-opioid receptors in the brain and spinal cord, which inhibits the release of pain-producing neurotransmitters such as substance P and glutamate. This leads to a decrease in the transmission of pain signals to the brain, resulting in analgesia. Additionally, morphine's euphoric effects are also mediated through μ-opioid receptor activation.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because morphine's analgesic effects are not primarily mediated through GABA receptors, although it can have a sedative effect on the central nervous system.
**Option B:** This option is incorrect because morphine does not primarily act as a local anesthetic; its effects are systemic and mediated through opioid receptors in the central nervous system.
**Option C:** This option is incorrect because while morphine can cause respiratory depression, this is not its primary mechanism of action; rather, it is a side effect of its central nervous system effects.
**Clinical Pearl / High-Yield Fact**
Morphine and other opioids can cause physical dependence and addiction due to their ability to activate the brain's reward system and release dopamine.
**Correct Answer:** C.