Exam 3: Effect of drugs
A psychoactive drug is a chemical substance that acts primarily on the central nervous system where it alters brain function resulting in temporary changes in perception, mood, consciousness and behaviour. Most of these drugs were originally developed to be used therapeutically as medication. Because psychoactive substances bring about subjective changes in consciousness and mood that the user may find pleasant (e.g. euphoria) or advantageous (e.g. increased alertness), many psychoactive substances are abused, that is, used outside of the guidance of a medical professional and for reasons other than their original purpose. With sustained use physical dependence may develop, making the cycle of abuse even more difficult to interrupt. Examples of psychoactive drugs include tobacco, cannabis, amphetamines, ecstasy, cocaine, heroin etc.
Most drugs that affect the nervous system influence the transmission of nerve impulses across synapses. These drugs can be classified into two types:
Excitory drugs:
Such as amphetamines/ecstasy/cocaine/caffeine/nicotine = "amplify" the process of synaptic transmission
Inhibitory drugs:
Such as Beta-blockers (mainly used to treat heart disease) and alcohol = modify the effects that the neurotransmitters have on the post-synaptic membrane = "reduce" the process of synaptic trabsmission
Amplification at the synapse may be due to chemicals mimicking the action of natural transmitters. That is, they have the same shape and affect the post-synaptic neurone in the same way that the transmitter would. They also may prevent the breakdown of the real neurotransmitter, for example, by inhibiting the enzyme that normally does this.
• Organophosphorous insecticides block the enzyme (acetylcholinesterase) that breaks down the neurotransmitter (acetylcholine) once it is attached to the receptor proteins of the post-synaptic membrane (acetylcholine normally gets broken down into choline and ethanoic acid which get recycled back into the pre-synaptic bulb). This inhibition prolongs the effect of the neurotransmitters. Without acetylcholinesterase activity (because it is being inhibited by the organophosphate), the acetylcholine remains in the synaptic cleft and causes repeated firing of the postsynaptic neurone. If the inhibitor is acting at a neuromuscular junction repeated contractions of the muscle occurs. That is, the nervous system becomes overactive and muscles contract uncontrollably.
• Drugs like amphetamine ("speed") and its related drug ecstasy (please note that "MDMA" is the active component of ecstasy) are excitory drugs that stimulate the release of neurotransmitters such as noradrenaline. Chemicals such as caffeine and nicotine also increase excitation of the postsynaptic membranes (caffeine stimulates more ATP in the pre-synaptic bulb meaning more neurotransmitter can be made and released into the synaptic cleft whereas nicotine binds directly to receptor proteins on the post-synaptic membrane causing Na+ ion channels to open).
If drug is taken over a period of time then the synapse may be modified to adjust to its use. For example, if the drug blocks particular receptors at synapses, then new receptors may be made to make up for the ones that are no longer in use. This means that more drug has to be taken to have the same effect. This is known as tolerance to the drug. An increasing tolerance indicates an increase in dependency on the drug. Dependency occurs when, as a result of changes to the CNS, the individual can no longer manage without the drug. A distinction may be made between physical dependency and psychological dependency.
Physical dependency occurs because there have been changes in the structure and the way the neurones of the brain work. If the individual stops taking the drug they suffer from withdrawal symptoms. Withdrawal from heroin produce some of the worst withdrawal symptoms.
Psychological dependency is due to what is happening in the brain as a result of taking the drug.
The individual does not experience withdrawal symptoms but they constantly crave the drug, in a similar way in which a person feels when they are very hungry or thirsty. Alcohol is an example of a drug to which both physical and psychological dependency may develop. It also affects neurotransmitters in the brain. It is a depressant and if drunk in large amounts can kill.
Inhibition of various areas of the brain causes drowsiness and eventually unconsciousness. It can cause coma. Regular high consumption over many years may damage the liver, causing cirrhosis. This condition normally results in death.
A psychoactive drug is a chemical substance that acts primarily on the central nervous system where it alters brain function resulting in temporary changes in perception, mood, consciousness and behaviour. Most of these drugs were originally developed to be used therapeutically as medication. Because psychoactive substances bring about subjective changes in consciousness and mood that the user may find pleasant (e.g. euphoria) or advantageous (e.g. increased alertness), many psychoactive substances are abused, that is, used outside of the guidance of a medical professional and for reasons other than their original purpose. With sustained use physical dependence may develop, making the cycle of abuse even more difficult to interrupt. Examples of psychoactive drugs include tobacco, cannabis, amphetamines, ecstasy, cocaine, heroin etc.
Most drugs that affect the nervous system influence the transmission of nerve impulses across synapses. These drugs can be classified into two types:
Excitory drugs:
Such as amphetamines/ecstasy/cocaine/caffeine/nicotine = "amplify" the process of synaptic transmission
Inhibitory drugs:
Such as Beta-blockers (mainly used to treat heart disease) and alcohol = modify the effects that the neurotransmitters have on the post-synaptic membrane = "reduce" the process of synaptic trabsmission
Amplification at the synapse may be due to chemicals mimicking the action of natural transmitters. That is, they have the same shape and affect the post-synaptic neurone in the same way that the transmitter would. They also may prevent the breakdown of the real neurotransmitter, for example, by inhibiting the enzyme that normally does this.
• Organophosphorous insecticides block the enzyme (acetylcholinesterase) that breaks down the neurotransmitter (acetylcholine) once it is attached to the receptor proteins of the post-synaptic membrane (acetylcholine normally gets broken down into choline and ethanoic acid which get recycled back into the pre-synaptic bulb). This inhibition prolongs the effect of the neurotransmitters. Without acetylcholinesterase activity (because it is being inhibited by the organophosphate), the acetylcholine remains in the synaptic cleft and causes repeated firing of the postsynaptic neurone. If the inhibitor is acting at a neuromuscular junction repeated contractions of the muscle occurs. That is, the nervous system becomes overactive and muscles contract uncontrollably.
• Drugs like amphetamine ("speed") and its related drug ecstasy (please note that "MDMA" is the active component of ecstasy) are excitory drugs that stimulate the release of neurotransmitters such as noradrenaline. Chemicals such as caffeine and nicotine also increase excitation of the postsynaptic membranes (caffeine stimulates more ATP in the pre-synaptic bulb meaning more neurotransmitter can be made and released into the synaptic cleft whereas nicotine binds directly to receptor proteins on the post-synaptic membrane causing Na+ ion channels to open).
If drug is taken over a period of time then the synapse may be modified to adjust to its use. For example, if the drug blocks particular receptors at synapses, then new receptors may be made to make up for the ones that are no longer in use. This means that more drug has to be taken to have the same effect. This is known as tolerance to the drug. An increasing tolerance indicates an increase in dependency on the drug. Dependency occurs when, as a result of changes to the CNS, the individual can no longer manage without the drug. A distinction may be made between physical dependency and psychological dependency.
Physical dependency occurs because there have been changes in the structure and the way the neurones of the brain work. If the individual stops taking the drug they suffer from withdrawal symptoms. Withdrawal from heroin produce some of the worst withdrawal symptoms.
Psychological dependency is due to what is happening in the brain as a result of taking the drug.
The individual does not experience withdrawal symptoms but they constantly crave the drug, in a similar way in which a person feels when they are very hungry or thirsty. Alcohol is an example of a drug to which both physical and psychological dependency may develop. It also affects neurotransmitters in the brain. It is a depressant and if drunk in large amounts can kill.
Inhibition of various areas of the brain causes drowsiness and eventually unconsciousness. It can cause coma. Regular high consumption over many years may damage the liver, causing cirrhosis. This condition normally results in death.