Anatomy and Physiology Advanced of CK-12-Biology-Advanced-Concepts Test Bank Study Guide

1.16. Drugs and the Nervous System - Advanced Roasted coffee beans. Coffee beans are a common source of the stimulant caf- feine. Other plant sources include the leaves of tea, cocoa, yerba mate, and guarana plants. These plants use caffeine as a means of protection against being eaten. The caffeine in the leaves of these plants can paralyze and kill the insects that feed upon them. Drugs and the Brain: How Psychoactive Drugs Work How we perceive and respond to stimuli is a result of neurons sending action potentials and neurotransmitters to both each other and other cells in the body. Psychoactive drugs affect how neurons communicate with each other. These drug molecules can alter neurotransmission by blocking receptor proteins, mimicking neurotransmitters, or changing the amount of neurotransmitters in a synapse, as shown in the Figure 1.49, by blocking reuptake. In this way, a psychoactive drug can change how we feel, think, and interact with the world. Sometimes these effects are beneficial, such as taking a prescribed painkiller (hydrocodone, for example) to ease the pain of a broken bone. Sometimes the effects are harmful, which could happen if the person continued to take the powerful painkiller long after their broken bone had healed. Some examples of psychoactive medicines are listed in the Table 1.11. TABLE 1.11: Some Psychoactive Medicines and Their Uses Type Uses Example Action Anesthetics Block pain and other sen- sations. Often induce un- consciousness, which al- lows patients to undergo medical procedures. Lidocaine and nitrous ox- ide. Mimic the inhibitory neu- rotransmitter GABA or increase the amount of GABA in the synapse, which prevents an action potential. 90 Chapter 1. Anatomy and Physiology - Advanced TABLE 1.11: (continued) Type Uses Example Action Painkillers (analgesics) Reduce the sensation of pain. Includes narcotics and non-steroidal anti- inflammatory drugs (NSAIDS). Narcotics: morphine and codeine. NSAIDS: aspirin and acetaminophen (paracetamol). Drug molecules mimic endogenous opioids (“nat- ural painkillers”), such as endorphins, by binding to opioid receptors. Antidepressants Antidepressants are used to treat disorders such as clinical depression, anxi- ety, and eating disorders. Selective Serotonin Re- uptake Inhibitors (SSRIs) and Monoamine oxidase inhibitors (MAOIs). SSRIs: Block the up- take of the neurotransmit- ter serotonin by the presy- naptic neuron. MAOIs: Prevent an enzyme from breaking down serotonin in the synapse. Both actions result in an in- crease of serotonin in the synapse. Stimulants Used to treat disorders such as attention deficit disorder and to suppress the appetite. Antipsychotics Used to treat psychoses such as schizophrenia and mania. Amphetamine salts. Increases extracellular levels of dopamine, norepinephrine, and serotonin by various means. Chlorpromazine. Blocks dopamine recep- tors in postsynaptic neu- rons. Cough medicines (antitus- sives). Used to treat persistent coughing. Dextromethorphan (DXM) and codeine. Inhibits the action of the NMDA receptor in the postsynaptic cell. Reduces action potentials and is similar in action to anesthetics. 91 1.16. Drugs and the Nervous System - Advanced Drug Abuse The release of neurotransmitters into the synaptic cleft. Depending on its method of action, a psychoactive substance may block the receptors on the postsynaptic neuron, block reuptake, or affect neuro- transmitter synthesis in the presynaptic neuron. Psychoactive drugs bring about changes in mood and feelings that a user may find desirable; therefore, many psychoactive substances are abused. Drug abuse is the repeated use of a drug without advice or guidance of a medical professional or use for reasons other than for what the drug was originally intended. With continued use of a drug, a person might find that they cannot function normally without the drug; this is a state called physical dependence. However, note that physical dependence is not in itself bad. For example, a person who has diabetes is physically dependent on insulin injections. Their body cannot work properly without it. Emotionally or mentally needing a drug to be able to function normally is called psychological dependence. When a person continues to take a psychoactive drug, they eventually need to take larger doses of the drug to get the desired effect. This process is known as building a tolerance to the drug. Drug tolerance can involve both psychological and physical factors. A person who is abusing a drug may eventually lose control of their drug-taking behavior. This is partly due to the changes the drug has caused in their brain and partly due to learned drug-abuse behaviors (such as stealing and lying to get money or drugs). In the state of addiction, a drug addict’s life and activities revolve around getting more of the drug to feed their habit, even if it leads to severe consequences such as getting arrested, dropping out of school, or isolation from friends and family. In a person who is addicted to a drug, the pattern of increasing doses due to tolerance can lead to a drug overdose (also known as an OD). A drug overdose is generally considered harmful and may lead to death. Drug dependence and addiction are caused by changes in the way neurons in the CNS send and receive neurotransmitters. It is for this reason that dependency and addiction are treated as brain disorders by medical professionals. Several classes of psychoactive drugs are commonly abused. Stimulants, such as cocaine, nicotine, and am- phetamine, increase the activity of the sympathetic nervous system, the central nervous system, or both. Stimulants generally increase heart rate, blood pressure, and one’s sense of alertness. Some stimulants, such as caffeine, are used medicinally to increase or maintain alertness and to counteract fatigue. High doses of stimulants can be fatal. A common source of nicotine is cigarette tobacco, which is shown in the Figure 1.50. Hypnotics, also known as depressants, such as alcohol, codeine, barbiturates, and benzodiazepines, generally decrease the activity of the central nervous system. Depressants slow down brain function and give a drowsy or calm feeling. However, taking too much of a depressant drug can cause dangerously slow breathing and heart rates and may result in death. Many depressants acting on the CNS do so by increasing the activity of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA), although there are many receptors that are affected by different depressants. GABA calms the activity of the CNS and promotes sleep. Drugs that stimulate the activity of this amino acid slow down brain function and cause a drowsy or calm feeling, so depressants are generally prescribed to relieve symptoms of anxiety or insomnia. 92 Chapter 1. Anatomy and Physiology - Advanced