Chapter 4 Visual Summary

The function of the classical synapse is to communicate information from a presynaptic neuron to a postsynaptic cell. It does so by converting an electrical signal—the action potential—into secretion of a neurotransmitter that crosses to the postsynaptic cell and alters that cell's functioning. Review Figure 4.1, Animation 4.2

Neurotransmitters exert their effects via neurotransmitter receptors; these are also the site of action for many psychoactive drugs. Most transmitters have several different subtypes of receptors, which may be individually targeted by drugs. A given neurotransmitter may normally bind several different subtypes of receptors. Review Figure 4.2, Table 4.2

The major categories of neurotransmitters are amine, amino acid, peptide, and soluble gas neurotransmitters. Neurotransmitter systems form complex, overlapping patterns of projections throughout the brain. Review Figure 4.3 and Figure 4.4, Table 4.1, Animation 4.3, Activity 4.1

Drugs classified as agonists activate transmitter pathways, and antagonists block transmitter pathways. Repeated exposure to drugs may cause a compensatory down-regulation (decrease) or up-regulation (increase) in the number of receptors. Changes in receptor density are one mechanism of drug tolerance. Review Figure 4.5, Animation 4.4

The dose-response curve (DRC) quantifies the relationship between doses of a drug and its physiological effects, and it can be used to deduce characteristics such as drug potency and safety. Review Figure 4.6

Psychoactive drugs have three main presynaptic actions: some drugs alter transmitter synthesis, others alter transmitter release, and some block the clearance of transmitter after it has been released. Review Figure 4.7

Many psychoactive drugs have postsynaptic effects, especially activation or blockade of postsynaptic receptors. Other drugs affect metabolic processes within the postsynaptic neuron, such as alterations in second-messenger systems, or changes in the production of crucial proteins (e.g., transmitter receptors). Most antipsychotic medications block postsynaptic dopamine (DA) receptors, but some also block serotonin (5-HT) receptors. Review Figure 4.8

Opiates such as morphine are potent painkillers; the brain also makes its own endogenous opioids with a variety of effects. Opiates act on specific opioid receptors, especially in a major pain pathway that includes the periaqueductal gray. Review Figure 4.10

The active ingredient in marijuana—delta-9-tetrahydrocannabinol, or THC—acts on cannabinoid receptors to produce its effects. Anandamide is an endocannabinoid that acts at cannabinoid receptors to affect mood, pain sensitivity, blood pressure, and other functions. Review Figure 4.11

Some stimulants, such as nicotine, imitate an excitatory synaptic transmitter. Others, such as amphetamine, cause the release of excitatory synaptic transmitters and block the reuptake of transmitters. Cocaine causes the release of transmitters, especially dopamine, in wide regions of the brain. Review Figure 4.12

Alcohol acts on gamma-aminobutyric acid (GABA) receptors to produce some of its effects. In moderation, alcohol has beneficial effects; in higher doses it is very harmful, damaging neurons in many areas of the brain. Review Figure 4.13 and Figure 4.14

Some drugs are called hallucinogens because they alter sensory perception and produce peculiar experiences. Although hallucinogens vary in their actions, many share activity at serotonin receptors in the visual cortex, perhaps explaining their effects on visual perception. Review Figure 4.15

Substance abuse and dependence (addiction) are being studied intensively, and several explanatory models have been proposed. The positive reward model, based on the observation that animals will work very hard to self-administer highly addictive drugs, has received the most support from research. Review Figure 4.16, Table 4.5

A dopamine-based neural pathway from the ventral tegmental area to the nucleus accumbens appears to be a system for experiencing pleasure and reward. Researchers believe that this reward system plays an important role in the formation of addictions. Some experimental treatments for addiction involve blocking the reward signal from drugs. Review Figure 4.17 and Figure 4.18

    Previous 1 of 14 Next