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The Human Body


Cell that carries messages throughout the nervous system.


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

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.

Cell Body

Largest part of a typical neuron; conatins the nucleus and much of the cytoplasm.


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

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 environment.

Feedback Inhibition

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


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.


A photoreceptor that responds to the 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.


A signal to which an organism responds.


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.

Levels of organization in multicellular organisms

cell, tissue, organ, organ system

Nervous system

coordinates the body's response to changes in its internal and external environments.

Integumentary System

skin etc., serves as a barrier, regulates temp, protects against uv radiation

Respiratory system

provides oxygen and removes carbon dioxide from the body

Digestive System

Converts food into simpler molecules that can be used by cells of the body, absorbs food.

Excretory system

eliminates waste products of metabolism from the body, maintains homeostasis

Skeletal System

supports the body, protects internal organs, allows movement, stores mineral reserves, provides a site for blod cell formation

Muscular system

works with skeletal system to produce voluntary movement, help sto circulate blood and move food thru the digestive system

Endocrine system

controls growth, development, and reproduction.

Reproductive system

produces reproductive cells, in females nurtures and protects developing embryo

Lymphatic system

helps protect the body from disease, collects fluid lost from blood vessels and returns it to circulatory system


made from epithelial tissue - is a structure that makes and secretes a particular product

Sensory neurons

carry impulses from the sense organs to the spinal chord and brain.

Motor neurons

carry impulses from the brain and the spinal chord to muscles and glands.


connect sensory and motor neurons and carry impulses between them.

Axon terminals

axon ends in a small series of swellings

Nerve impulse

begins when a neuron is stimulated by another neuron or by its environment.

Corpus callosum

band of tissue that connects the hemispheres of the brain.

Gray matter

consists of desnsely packed nerve cell bodies.

Cerebral cortex

outer surface of cerebrum.

Peripheral nervous system

Divided into sensory and motor divisions.

Central nervous system

relays messages, processes info, analyzes info. Consists of the brain and spinal chord.

Somatic nervous system

regulates conscious activities. Also involved with reflex arcs.

Autonomic nervous system

regulates involuntary activities like hearbeats.

Sympathetic and parasympathetic nervous systems

both control autonomic nervous system responsibilities oppositely.

Sensory division

transmits impulses from sense organs to the c.n.s.

Motor division

transmits imuplses from the central nervous system to muscles or glands. Divided into somatic nervous system and autonomic nervous system.

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