psych

• nature-nurture issue


  the longstanding controversy over the relative contributions that genes and experience make to the development of psychological traits and behaviors. Today's science views traits and behaviors as arising from the interaction of nature and nurture.
• natural selection


  the principle that the inherited traits enabling an organism to survive and reproduce in a particular environment will (in competition with other trait variations) most likely be passed on to succeeding generations.
• evolutionary psychology


  the study of the evolution of behavior and the mind, using principles of natural selection.
• behavior genetics


  the study of the relative power and limits of genetic and environmental influences on behavior.
• mutation


  a random error in gene replication that leads to a change.
• environment


  every nongenetic influence, from prenatal nutrition to our experiences of the people and things around us.
• heredity


  the genetic transfer of characteristics from parents to offspring.
• genes


  the biochemical units of heredity.
• genome


  the complete instructions for making an organism.
• identical (monozygotic) twins


  individuals who developed from a single fertilized egg that split in two, creating two genetically identical organisms.
• fraternal (dizygotic) twins


  individuals who developed from separate fertilized eggs. They are genetically no closer than ordinary siblings, but they shared a prenatal environment.
• interaction


  the interplay that occurs when the effect of one factor (such as environment) depends on another factor (such as heredity).
• epigenetics


  "above" or "in addition to" (epi) genetics; the study of the molecular mechanisms by which environments can influence genetic expression (without a DNA change).
• nervous system


  the body's speedy, electrochemical communication network, consisting of all the nerve cells of the peripheral and central nervous systems.
• central nervous system (CNS)


  the brain and spinal cord.
• peripheral nervous system (PNS)


  the sensory and motor neurons that connect the central nervous system (CNS) to the rest of the body.
• nerves


  bundled axons that form neural cables connecting the central nervous system with muscles, glands, and sensory organs.
• sensory (afferent) neurons


  neurons that carry incoming information from the body's tissues and sensory receptors to the brain and spinal cord.
• motor (efferent) neurons


  neurons that carry outgoing information from the brain and spinal cord to the muscles and glands.
• interneurons


  neurons within the brain and spinal cord; they communicate internally and process information between the sensory inputs and motor outputs.
• somatic nervous system


  the division of the peripheral nervous system that controls the body's skeletal muscles. Also called the skeletal nervous system.
• autonomic [aw-tuh-NAHM-ik] nervous system (ANS)


  the part of the peripheral nervous system that controls the glands and the muscles of the internal organs (such as the heart). Its sympathetic division arouses; its parasympathetic division calms.
• sympathetic nervous system


  the division of the autonomic nervous system that arouses the body, mobilizing its energy.
• parasympathetic nervous system


  the division of the autonomic nervous system that calms the body, conserving its energy.
• reflex


  a simple, automatic response to a sensory stimulus, such as the knee-jerk reflex.
• neuron


  a nerve cell; the basic building block of the nervous system.
• cell body


  the part of a neuron that contains the nucleus; the cell's life-support center.
• dendrites


  a neuron's often bushy, branching extensions that receive and integrate messages, conducting impulses toward the cell body.
• axon


  the segmented neuron extension that passes messages through its branches to other neurons or to muscles or glands.
• myelin [MY-uh-lin] sheath


  a fatty tissue layer segmentally encasing the axons of some neurons; it enables vastly greater transmission speed as neural impulses hop from one node to the next.
• glial cells (glia)


  cells in the nervous system that support, nourish, and protect neurons; they may also play a role in learning, thinking, and memory.
• action potential


  a neural impulse; a brief electrical charge that travels down an axon.
• threshold


  the level of stimulation required to trigger a neural impulse.
• refractory period


  in neural processing, a brief resting pause that occurs after a neuron has fired; subsequent action potentials cannot occur until the axon returns to its resting state.
• all-or-none response


  a neuron's reaction of either firing (with a full-strength response) or not firing.
• synapse [SIN-aps]


  the junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The tiny gap at this junction is called the synaptic gap or synaptic cleft.
• neurotransmitters


  chemical messengers that cross the synaptic gap between neurons. When released by the sending neuron, neurotransmitters travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing whether that neuron will generate a neural impulse.
• reuptake


  a neurotransmitter's reabsorption by the sending neuron.
• endorphins [en-DOR-fins]


  "morphine within"; natural, opioid-like neurotransmitters linked to pain control and to pleasure.
• agonist


  a molecule that increases a neurotransmitter's action.