What Is the Genetic Basis of Psychological Science?
The human genome is a genetic blueprint consisting of 23 pairs of chromosomes organized into segments of DNA called genes. The basic mechanism of heredity was worked out through the careful observations of Gregor Mendel, a monk working with pea plants around 1866. As you review this material, be sure you understand the interaction between dominant and recessive genes and know the difference between an organism's genotype (its genetic makeup) and its phenotype (its observable physical characteristics). Sexual reproduction is the source of genetic variation. Be sure you can differentiate between meiosis (the process by which cells split to form gametes) and mitosis (the process by which cells divide for growth and development).

Genetic variation occurs through mutation, which includes errors in the duplication process. Behavioral geneticists study how genes and behavior interact to influence psychological activity. Some of the techniques that behavioral geneticists use are twin studies, adoption studies, and the comparison of identical twins who have been raised apart from one another. The goal of this research is to determine the heritability of a trait or characteristic. Heritability, which is not the same as heredity, refers to the amount of observed variation in a trait or characteristic that can be attributed to genetic variation. Researchers investigating the interaction of our genes and our environment have shown that the environment affects our genetic makeup and vice versa.

How Does the Nervous System Operate?
Nerve cells, also known as neurons, are the basic units of the nervous system. There are three different types of neurons: sensory neurons, which carry information from our sense organs to our brain; motor neurons, which carry signals from our brains to our muscles; and interneurons, which carry signals between neurons. While neurons come in a variety of shapes and sizes, they share the same basic structure of dendrites, cell body, axon, and terminal buttons. Communication between neurons is an electrochemical process: Prompted by an electrical signal, one neuron releases a chemical that in turn effects the electrical state an adjacent neuron. Put simply, the neuron at rest has a slight negative charge, known as a resting membrane potential. Stimulation from other neurons changes the electrical state of the neuron making it more or less negative. If there is sufficient depolarization of the neuron, an action potential is generated, which travels down the length of the axon and causes the release of neurotransmitters. These neurotransmitters then bind with receptors on the next neuron, causing changes in the electrical state of that neuron and thus beginning the process all over again. After you have read through this section of the chapter, you should be able to explain the entire process from start to finish, and you should be familiar with terms such as propagation, temporal and spatial summation, ion channels, synaptic vesicles, ionotropic and metabotropic receptors, reuptake, autoreception, and saltatory conduction.

How Do Neurotransmitters Influence Emotion, Thought, and Behavior?
Neurotransmitters are the chemicals that are released into the synapse and produce inhibitory or excitatory potentials in the postsynaptic neuron. Drugs that enhance the action of a particular neurotransmitter are known as agonists, and drugs that inhibit neuronal communication are known as antagonists. Although there are more than 60 different chemicals that are used in neuronal communication, the book focuses on just four categories of neurotransmitters: acetylcholine, monoamines, amino acids, and peptides.

How Are Neural Messages Integrated into Communication Systems?
Neurons and neurotransmitters are part of the communication system in the body known as the nervous system. The nervous system has two distinct parts: the central nervous system (CNS), composed of the brain and the spinal cord, and the peripheral nervous system (PNS). The PNS is itself composed of two parts: the somatic nervous system and the autonomic nervous system. The somatic nervous system transmits information between our CNS and our muscles and sense organs, and the autonomic nervous system regulates our body's internal environment. There are two divisions of the autonomic nervous system. The sympathetic division activates the body, expending energy for fight or flight. In contrast, the parasympathetic division of the autonomic nervous system relaxes the body and is involved in storing energy.

Like the nervous system, the endocrine system is a communication system. However, the endocrine system uses hormones, chemicals that are secreted by glands in the body, for communication. Because hormones travel through the bloodstream to reach their targets, they take longer to exert their effects and their effects are longer lasting than signals within the nervous system. The master gland in the body is the pituitary gland, and the pituitary in turn is controlled by the hypothalamus, a structure located at the base of the brain. Thus the hypothalamus is where the nervous system and the endocrine system intersect.

Students often find the material on the biological bases of behavior to be challenging, and this is not surprising, since the material is abstract and perhaps unfamiliar. By the same token, this chapter and the next introduce many new terms and processes that serve as a foundation for later learning; careful study now will save you grief later.