Definition: neurons that carry incoming information from the body's tissues and sensory receptors to the brain and spinal cord.

Definition: opium and its derivatives; they depress neural activity, temporarily lessening pain and anxiety.

Definition: registers and processes body touch and movement sensations.

Definition: an everyday term for compulsive substance use (and sometimes for dysfunctional behavior patterns, such as out-of-control gambling) that continue despite harmful consequences.

Definition: responsible for visual information processing.

Definition: individuals who developed from a single fertilized egg that split in two, creating two genetically identical organisms.

Definition: a neural impulse; a brief electrical charge that travels down an axon.

Definition: an amplified recording of the waves of electrical activity sweeping across the brain's surface. these waves are measured by electrodes placed on the scalp.

Definition: the genetic transfer of characteristics from parents to offspring.

Definition: 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.

Definition: the study of the evolution of behavior and the mind, using principles of natural selection.

Definition: the junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron.

Definition: the body's ultimate control and information-processing center.

Definition: drugs that depress central nervous system activity, reducing anxiety but impairing memory and judgment.

Definition: the division of the autonomic nervous system that arouses the body, mobilizing its energy.

Definition: a neurotransmitter's reabsorption by the sending neuron.

Definition: a molecule that increases a neurotransmitter's action.

Definition: the division of the peripheral nervous system that controls the body's skeletal muscles. also called the skeletal nervous system.

Definition: involved in higher mental functions such as learning, remembering, and speaking.

Definition: chemical messengers that are manufactured by the endocrine glands, travel through the bloodstream, and affect other tissues.

Definition: the diminishing effect with regular use of the same dose of a drug, requiring the user to take larger and larger doses before experiencing the drug's effect.

Definition: a nerve cell; the basic building block of the nervous system.

Definition: the longstanding controversy over the relative contributions that genes and experience make to the development of psychological traits and behaviors.

Definition: natural, opioid-like neurotransmitters linked to pain control and to pleasure.

Definition: drugs that excite neural activity and speed up body functions.

Definition: the hindbrain structure that controls heartbeat and breathing.

Definition: tissue destruction. may occur naturally (from disease or trauma), during surgery, or experimentally (using electrodes to destroy brain cells).

Definition: a nerve network that plays an important role in controlling arousal.

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

Definition: the hindbrain's "little brain" responsible for processing sensory input, coordinating movement and balance.

Definition: a neural structure directing maintenance activities, linked to emotion and reward.

Definition: a chemical substance that alters the brain, causing changes in perceptions and moods.

Definition: the level of stimulation required to trigger a neural impulse.

Definition: 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.

Definition: neural system that includes the amygdala, hypothalamus, and hippocampus; associated with emotions and drives.

Definition: responsible for higher-order thinking, linguistic processing, and executive functioning.

Definition: a molecule that inhibits or blocks a neurotransmitter's action.

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

Definition: the body's speedy, electrochemical communication network, consisting of all the nerve cells of the peripheral and central nervous systems.

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

Definition: the large band of neural fibers connecting the two brain hemispheres.

Definition: a condition resulting from surgery that separates the brain's two hemispheres.

Definition: neurons within the brain and spinal cord; they communicate internally and process information between the sensory inputs and motor outputs.

Definition: the body's 'slow' chemical communication system; a set of glands that secrete hormones into the bloodstream.

Definition: the division of the autonomic nervous system that calms the body, conserving its energy.

Definition: the discomfort and distress that follow discontinuing an addictive drug or behavior.

Definition: the brain and spinal cord.

Definition: the sensory control center, directs messages to sensory receiving areas in the cortex.

Definition: the central core of the brain, responsible for automatic survival functions.

Definition: drugs that reduce neural activity and slow body functions.

Definition: a disorder characterized by continued substance use despite resulting life disruption.

Definition: process sensory input for touch and body position.

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

Definition: the brain's ability to change, especially during childhood, by reorganizing after damage or by building new pathways based on experience.

Definition: chemical messengers that cross the synaptic gap between neurons.

Definition: controls voluntary movements.

Definition: two neural clusters in the limbic system linked to emotion.

Definition: a random error in gene replication that leads to a change.

Definition: a neural center in the limbic system that helps process explicit memories for storage.

Definition: the biochemical units of heredity.

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

Definition: neurons that carry outgoing information from the brain and spinal cord to the muscles and glands.

Definition: 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.

Definition: bundled axons that form neural cables connecting the central nervous system with muscles, glands, and sensory organs.

Definition: psychedelic drugs that distort perceptions and evoke sensory images in the absence of sensory input.

Definition: 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.

Definition: process auditory information and enable language processing.

Definition: a neuron's reaction of either firing (with a full-strength response) or not firing.