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Brains, Biology, and Behavior


action potential

signal sent by a neuron once inputs exceed a threshold


substance that excites or stimulates

all-or-none response

principle that the strength of a neural response does not depend on the strength of the stimulus. Neurons either fire or do not fire in response to stimulation; there are no gradations.


substance that inhibits or suppresses

association area

area of the cerebral cortex that interprets inputs from multiple sources, decides how to respond, and puts the decision into action

central nervous system (CNS)

brain and spinal cord


structure that contains DNA, the genetic material that is passed from one generation to the next

computed tomography (CT) scan

3-D visual image of the brain constructed by using X-rays to detect differences in tissue density

deoxyribonucleic acid (DNA)

organic molecule containing coded instructions for the life processes of an organism

electroencephalogram (EEG)

recording of the brain's electrical activity made by placing electrodes on the scalp

endocrine system

body system that consists of different glands used to produce hormones that regulate body functions


study of heritable changes in the expression of genes that are caused by the environment

functional magnetic resonance imaging (fMRI)

brain imaging technique that uses a strong magnetic field and radio waves to identify which areas of the brain are active while a person engages in a cognitive task


unit of heritable material that codes for a particular trait

glial cell

type of cell that makes up most of the brain tissue, responsible for providing nutrients to neurons and removing debris


proportion of phenotypic variance attributable to genetic variance


chemical secreted by an endocrine gland that triggers a response from a particular type of cell or tissue

limbic system

brain region involved in motivation, emotion, learning, and memory

magnetic resonance imaging (MRI)

imaging technique that uses a strong magnetic field and radio waves to produce a detailed image of the brain or other body parts

natural selection

mechanism of evolution in which individuals that are better adapted to their environment survive and reproduce more successfully than less well adapted individuals do


process by which new neurons are formed in the brain


cell in the nervous tissue that transmits electrical and chemical signals throughout the body


hormone released into the gap between the axon of a neuron and another neuron's dendrites

peripheral nervous system

system of neurons outside the brain and spinal cord that transmits messages throughout the body


observable characteristics of an organism that result from genetic and environmental influences


ability of brain circuitry to change as a function of experience

positron emission tomography (PET)

technique for mapping brain activity by measuring blood flow to brain regions experiencing heightened neural activity

refractory period

period after a neuron fires during which it cannot fire again

resting potential

difference in the voltage between the inside and outside of a neuron


space found between two nerve cells, across which neurotransmitters travel