Opioids Definition And Classification

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Opioids Definition and Classification
1. Definition
It is important to distinguish between opium, opiate and opioid. According to Vallejo et al. (2011, page E343), opium is a natural extract from the opium poppy, whereas opiates and opioids are its derivatives. Natural alkaloids derived of opium are generally called opiates, whereas opioids (opium-like) can be either natural or synthetic. The most common known opioids are morphine, codeine, fentanyl, hydrocodone, oxycodone, etc. (Vallejo et al., 2011, page E348 - E355)
2. Classification
Opioids can be categorized in different way according to distinct criteria.
a. Based on the nature of alkaloids
Opioids are classified into naturally occurring alkaloids and semi-synthetic opioids. Naturally
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Most of synapse transmissions are chemical transmission. Chemical transmission involves the release of neurotransmitters from the presynaptic neuron to the synaptic cleft. There are receptors that are specific for the neurotransmitters on the postsynaptic neuron. The pain receptor is called nociceptor. In the painful event, action potential sent from the soma comes down along the axon to its terminal. Neurotransmitters are released and bind to the nociceptors on the postsynaptic neuron. That neuron is activated and sends pain signals to our brain and spinal …show more content…
That is why most opioids have the analgesic effect. The inhibition of nerve impulses by opioids is a combination of different actions (Vallejo et al., 2011, page E344 - E345):
a. Presynaptic inhibition by inhibiting Calcium voltage channel
When calcium channel is inhibited, the amount of calcium going into the terminal is reduced. Vesicles of neurotransmitters lacking calcium cannot release the contents. The decrease in released neurotransmitters leads to less receptors bound by the ligands. Thus, this reduces the number of excitatory postsynaptic potentials and there will not enough potentials to trigger action potential in the postsynaptic neuron. (Vallejo et al., 2011, page E344 - E345)
b. Presynaptic inhibition by hyperpolarizing the presynaptic cell
The terminal of presynaptic neuron is hyperpolarized, which causes the amplitude of the action potential smaller. The number of neurotransmitters released depends on the magnitude of action potential. Therefore, less neurotransmitters are released to the cleft. Like the above case, the consequence of this event is that action potential cannot be triggered in the postsynaptic cell. (Vallejo et al., 2011, page E344 -

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