Morphine: Mental effects

Last modified: Saturday, 20. June 2009 - 1:07 pm

Morphine blocks the deep, aching perception of chronic pain, without interrupting the fast signals sent by an acute injury. As pain signals rise through the spinal cord to reach the brain, morphine interrupts them at a “relay station” within the core of the brain, called the thalamus. Morphine also blocks pain messages as they enter the spinal cord.
This interruption is not complete: the message of pain still reaches the brain. However, morphine blocks the emotions surrounding pain: people receiving the drug still know they are having pain, but it bothers them less.
Two views are offered to explain the action of morphine on pain. One says that the opiates work on all types of pain. The other says that opiates cannot work on a certain type of pain, called neuropathic, which is the pain created by damaged nerves themselves. When opiates do work in neuropathic pain, some experts say, it is only because the drugs improve the patient’s mood. In the early 1990s, one research team found that half of pains judged as neuropathic did respond to morphine. The changes in mood reflected the relief of pain, the researchers noted, regardless of the type of pain.
Researchers say that the euphoria produced by morphine is due to its action on dopamine. Dopamine is a neurotransmitter — nerve messenger — in the brain that acts in those parts of the brain that register pleasure.
The other Mental effects of morphine take place at the arousal centers of the brain, in the brainstem, to produce a sleepiness and relaxation. However, some patients experience restlessness instead of drowsiness, with increased limb movement rather than relaxation. Confusion and slurred speech almost always accompany morphine at higher doses. Meanwhile, the so-called “pinpoint pupils” of opiate overdose are created by morphine’s action on the iris, resulting in blurred vision and impaired ability to see in the dark.
Acting in the brainstem, as well as in the respiratory centers of the brain, morphine slows respiration and suppresses the cough reflex.

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