The Neural Bases of Behavior

1		Specialized cells called are the building blocks of the nervous system. Each neuron has three main parts. The contains the biochemical structures that keep the neuron alive, and the genetic information that controls cell development and function is in its nucleus. collect information from neighboring neurons and send it on to the cell body. The part of the neuron that conducts electrical impulses away from the cell body to other neurons, muscles, and glands is called the . Cells known as support neurons by holding them in place, manufacturing nutrient chemicals, and absorbing toxins and waste materials. A sudden reversal in the neuron’s membrane voltage is called an and the shift from negative to positive voltage is called . The depolarization process occurs when the dendrites of the cell are stimulated, resulting in small shifts in the cell membrane’s electrical potential, a shift called a . If the graded potential is large enough to reach the , an action potential occurs. Either an action potential occurs or its does not, according to the - - . When a neuron is stimulated, tiny protein structures called are activated. Sodium ion channels allow positively charged sodium ions to enter the interior of the cell, leading to the process of depolarization. Immediately after an impulse passes any point on the axon, a time period called an period occurs, during which another action potential cannot occur. A tubelike substance covering some axons in the brain and spinal cord is known as the . Neurons communicate through synaptic transmission. Chemical substances called carry messages across the synapse and bind to . Once a neurotransmitter molecule binds to its receptor, it continues to activate or inhibit the neuron until deactivation occurs. One method of deactivation is , in which the transmitter molecules are taken back into the presynaptic neuron. There are many types of neurotransmitters. One involved in memory and muscle activity is . Abnormally high concentrations of have been found in the brains of schizophrenics. A class of neurotransmitter that is involved in reducing pain and increasing feelings of well-being are .

The Nervous System

2		There are three major types of neurons in the nervous system. neurons input messages from the sense organs to the spinal cord and brain, neurons carry impulses from the brain and spinal cord to the muscles and organs, and perform connective or associative functions within the nervous system. The division of the nervous system containing the brain and spinal cord is called the nervous system. The division that consists of all neurons connecting the CNS with the muscles, glands, and sensory receptors is called the nervous system. In turn, the PNS is divided into two systems. The nervous system consists of sensory and motor neurons while the nervous system regulates the body’s glands and involuntary functions such as breathing, circulation, and digestion. The autonomic nervous system consists of two branches. The branch activates or arouses bodily organs while the branch slows down body processes. Most nerves enter and leave the CNS via the spinal cord. Some simple stimulus-response sequences such as pulling away from a hot stove typically don’t involve the brain and are known as . Psychologists have used a number of methods of studying the brain. tests measure verbal and nonverbal behaviors that are known to be affected by brain damage. Sometimes researchers destroy neurons under controlled conditions or stimulate them with electrical current or with chemicals. Such techniques are known as techniques. The activity of large groups of neurons is often studied via an . The newest tools of discovery involve brain imaging. X-ray technology used to study brain structures are called scans. Pictures of brain activity involve the use of . A technique to measure both brain structures and function is called . The brain historically has been divided into three main divisions. The hindbrain consists of the brain stem and cerebellum. The brain stem is involved in life support. A structure that plays a major role in vital body functions such as heart rate and respiration is the . The is a bridge carrying nerve impulses between higher and lower levels of the nervous system. The cerebellum is concerned primarily with muscular coordination, learning, and memory. An important relay center for the visual and auditory systems is contained in the . Within the midbrain is the , which is involved in brain arousal, sleep, and attention. The size and complexity of the separates humans from lower animals. An important sensory relay station in the forebrain is the , while the plays a major role in motivational and emotional behavior. The system helps to coordinate behaviors needed to satisfy emotional and motivational urges. Within the limbic system are the , which is involved in the formation and storage of memories and the , which is linked to aggression and fear. The outermost layer of the brain is called the . Each hemisphere of the cortex is divided into four lobes, the , , , and lobes, each of which is associated with particular sensory and motor functions. Lying at the rear of the frontal lobe is the cortex, which is involved in controlling muscles. The sensory cortex receives sensory input. Two specific speech areas are also located in the cortex. area is involved in speech comprehension while area is involved in the production of speech. The is involved in the highest levels of mental functions. People who suffer from , the inability to identify familiar objects often have suffered damage to their association cortex. Executive functions such as goal setting, judgment, and planning may be controlled by the cortex. The brain is typically also divided into two hemispheres: the left and the right. The is a bridge that helps the two hemispheres communicate and work together. When a function is located more in one hemisphere than the other, it is known as . "Split-brain" research designed to look at the relative functions of the hemispheres involves studying the roles of the corpus callosum and the . The brain as a structure develops over time. The ability of neurons to change in structure and function is known as .

Nervous System Interactions with the Endocrine and Immune Systems

3		The system consists of numerous glands distributed throughout the body. The system conveys information via , which are chemical messengers secreted by the glands into the bloodstream. The glands secrete stress hormones, which mobilize the body’s immune system. When foreign substances known as invade the body, the immune system produces antibodies to destroy them. Problems arise with both an underactive and an overactive immune system. An overactive response known as an reaction results when the immune system incorrectly identifies part of the body as an enemy and attacks it.

Genetic Influences on Behavior

4		The specific makeup of the individual is known as the , while the observable characteristics produced by that genetic endowment is known as the person’s . Some genes are dominant and some are recessive. If a gene in the pair received from both the mother and the father is , then the characteristic it controls will be displayed in the phenotype. If the gene received from one parent is , then the characteristic will not show up unless the gene received from the other parent is also . When many gene pairs combine to create a single phenotypic trait, the process is called . Geneticists today are mapping the human genome and studying how the genes affect human behavior. Genetic engineering involves duplicating and modifying the structures of genes. In , enzymes are used to cut DNA into pieces, after which the DNA is combined with DNA from another organism and then is inserted into a host organism. Behavior geneticists study how hereditary and environmental factors work together to influence human behavior. Researchers will often try to determine a characteristic’s , or co-occurrence in people who are genetically related to each other. A type of study in which a person who was adopted early in life is compared on a characteristic with a biological relative is called an study. Studies of the concordance rates of twins are called studies. Such studies help researchers to understand the relative influences of heredity and environment on behavior by comparing the concordance rates for identical (monozygotic) twins with those for fraternal (dizygotic) twins.