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Chapter 9 Nervous System

Terms

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Any change or signal in the environment that can make an organism react in some way.
stimulus
What the body does in reaction to a stimulus
response
A cell that carries messages through the nervous system.
neuron
The message carried by a neuron.
nerve impulse
A threadlike extension of a neuron that carries nerve impulses toward the cell body.
dendrite
A threadlike extension of a neuron that carries nerve impulses away from the cell body.
axon
A bundle of nerve fibers.
nerve
A neuron that picks up stimuli from the internal or external environment and converts each stimulus into a nerve impulse.
sensory neuron
A neuron that carries nerve impulses from one neuron to another.
interneuron
A neuron that sends an impulse to a muscle, causing the muscle to contract.
motor neuron
The tiny space between the tip of an axon and the next structure.
synapse
The brain and spinal cord; the control center of the body.
central nervous system
All the nerves located outside the central nervous system; connects the central nervous system to all parts of the body.
peripheral nervous system
The part of the central nervous system that is located in the skull and controls most functions in the body.
brain
The thick column of nerve tissue that is enclosed by the vertebrae and that links the brain to most of the nerves in the peripheral nervous system.
spinal cord
The part of the brain that interprets input from the senses, controls the movement of skeletal muscles, and carries out complex mental processes.
cerebrum
The part of the brain that coordinates the actions of the muscles and helps maintain balance.
cerebellum
The part of the brain that controls many body functions that occur automatically.
brainstem
The group of nerves that controls voluntary actions.
somatic nervous system
The group of nerves that controls involuntary actions.
autonomic nervous system
An automatic response that occurs very rapidly and without conscious control.
reflex
A bruiselike injury of the brain that occurs when the soft tissue of the cerebrum bumps against the skull.
concussion
The opening through which light enters the eye.
pupil
The circular structure that surrounds the pupil and regulates the amount of light entering the eye.
iris
The flexible structure that focuses light that has entered the eye.
lens
The layer of receptor cells at the back of the eye on which an image is focused; nerve impulses are sent from the retina to the brain.
retina
The condition in which nearby objects can be seen clearly but distant objects look blurry.
nearsightedness
The condition in which distant objects are seen clearly but nearby objects look blurry.
farsightedness
The membrane that separates the outer ear from the middle ear, and that vibrates when sound waves strike it.
eardrum
A snail-shaped tube in the inner ear lined with sound receptors; nerve impulses are sent from the cochlea to the brain.
cochlea
Structures in the inner ear that are responsible for the sense of balance.
semicircular canal
Any chemical that causes changes in a person's body or behavior.
drug
The deliberate misuse of drugs for purposes other than appropriate medical ones.
drug abuse
A state in which a drug user, after repeatedly taking a drug, needs larger and larger doses of the drug to produce the same effect.
tolerance
A period of adjustment that occurs when a drug-dependent person stops taking the drug.
withdrawal
A drug that slows down the activity of the central nervous system.
depressant
A drug that speeds up body processes.
stimulant
Synthetic chemicals that are similar to hormones produced in the body and that may increase muscle size and cause mood swings.
anabolic steroids
A disease in which a person is both physically addicted to and emotionally dependent on alcohol.
alcoholism

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