| A | B |
|---|
| stimulus | A change in an organism's surroundings that cause the organism to react |
| response | An action or change in the behavior that occurs as a result of a stimulus |
| neuron | A cell that carries messages through the nervous system |
| nerve impulse | The message carried by a neuron |
| dendrite | A threadlike extension of a neuron that carries nerve impulses toward the cell body |
| axon | A threadlike extension of a neuron that carries nerve impulses away from the body cell |
| sensory neuron | A neuron that picks up stimuli from the internal or external environment and converts each stimulus |
| interneuron | A neuron that carries the nerve impulses from one neuron to another |
| synapse | The tiny space between the tip of an axon and the nerve structure |
| central nervous system | The brain and spinal cord; the control center of the body |
| peripheral nervous sytem | All of the nerves located outside the central nervous system |
| spinal cord | The thick column of nerve tissue that is enclosed by the vertebrae and that links |
| cerebrum | The part of the brain that interprets input from the senses, controls the movement of skeletal muscles, and carries out complex mental processes |
| cerebellum | The part of the brain that coordinates the actions of muscles and and helps maintain balance |
| brainstem | The part of the brain that controls many body functions that occur automatically |
| somatic nervous system | The group of nerves that controls voluntary actions |
| reflex | An automatic response that occurs very rapidly and without conscious control |
| concussion | A bruiselike injury to the brain that occurs when the soft tissue of the cerebrum bumps against the skull |
| cornea | The clear tissue that covers the front of the eye |
| pupil | The opening through which light enters the eye |
| retina | 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 |
| nearsightedness | The condition in which nearby objects can be seen clearly but distant objects look blurry |
| farsightedness | The condition in which distant objects can be seen clearly but nearby objects look blurry |
| eardrum | The membrane that separates the outer ear from the middle ear, and that vibrates when sound waves strike it |
| cochlea | A snail-shaped tube in the inner ear lined with sound receptors: nerve impulses are sent from the cochlea to the brain |
| drug | Any chemical that causes changes in a person's body or behavior |
| drug abuse | The deliberate misuse of drugs for purposes other than appropriate medical ones |
| tolerance | 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 |
| withdrawal | A period of adjustment that occurs when a drug dependent person stops taking the drug |
| depressant | A drug that slows down the activity of the central nervous system |
| stimulants | A drug that speeds up the body processes |
| anabolic steriods | Synthetic chemicals that are similar to hormones produced in the body and that may increase muscle size and cause mood swings |
| alcoholism | A disease in which a person is both physically addicted to and emotionally dependant on alcohol |
| motor neuron | A neuron that sends an impulse to a muscle, causing the muscle to contract |
| autonomic nervous system | The group of nerves that controls involuntary actions |
