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specialized cell

cell that is uniquely suited to performing a particular function

epithelial tissue

tissue that covers the surface of the body and lines internal organs

connective tissue

tissue that holds organs in place and binds different parts of the body together

nervous tissue

tissue that receives messages from the body's external and internal environment, analyzes the data, and directs the response

muscle tissue

tissue that controls the internal movement of materials in the body, as well as external movement


process by which organisms maintain a relatively stable internal environment

feedback inhibition

process in which the product or result stops or limits the process


cell that carries messages throughout the nervous system

cell body

largest part of a typical neuron; contains the nucleus and much of the cytoplasm


extension of the cell body of a neuron that carries impulses from the environment or from other neurons toward the cell body


long fiber that carries impulses away from the cell body of a neuron

myelin sheath

insulating membrane surrounding the axon in some neurons

resting potential

electrical charge across the cell membrane of a resting neuron

action potential

reversal of charges across the cell membrane of a neuron; also called a nerve impulse


minimum level of a stimulus required to activate a neuron


location at which a neuron can transfer an impulse to another cell


chemical used by a neuron to transmit an impulse across a synapse to another cell


three layers of connective tissue in which the brain and spinal cord are wrapped

cerebrospinal fluid

fluid in the space between the meninges that acts as a shock absorber that protects the central nervous system


area of the brain responsible for all voluntary activities of the body


region of the brain that coordinates body movements

brain stem

structure that connects the brain and spinal cord; includes the medulla oblongata and the pons


brain structure that receives messages from the sense organs and relays the information to the proper region of the cerebrum for further processing


brain structure that acts as a control center for recognition and analysis of hunger, thirst, fatigue, anger, and body temperature


quick automatic response to a stimulus

reflex arc

sensory receptor, sensory neuron, motor neuron, and effector that are involved in a quick response to a stimulus

sensory receptor

neuron that reacts to a specific stimulus, such as light or sound, by sending impulses to other neurons and eventually to the central nervous system


small opening in the middle of the iris through which light enters the eye


transparent object behind the iris that changes shape to help adjust the eye's focus to see near or distant objects


innermost layer of the eye; contains photoreceptors


photoreceptor in eye that is sensitive to light but not to colors


in gymnosperms, a seed-bearing structure; in the retina of the eye, a photoreceptor that responds to light of different colors, producing color vision


fluid-filled part of the inner ear; sends nerve impulses to the brain through the cochlear nerve

semicircular canal

one of three structures within the inner ear that help monitor the position of the body

taste bud

sense organ that detects the flavor of a substance


any substance, other than food, that causes a change in the structure or function of the body


drug that speeds up the actions regulated by the nervous system


drug that decreases the rate of functions regulated by the brain

fetal alcohol syndrome

group of birth defects caused by the effects of alcohol on a fetus

drug abuse

intentional misuse of any drug for nonmedical purposes


uncontrollable dependence on a drug

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