Alzheimer’s disease: A progressive, neurodegenerative disease characterized by loss of function and death of nerve cells in several areas of the brain. This leads to loss of cognitive functions such as memory and language.
animal model: A laboratory animal used in research that simulates processes comparable to those that occur in humans.
axon: A long, branching outgrowth of a neuron that carries information, in the form of a nerve impulse, away from the cell body of the neuron. Each neuron has one axon, which can be over a foot long. A neuron delivers information to other cells through the axon terminals at the end of its axon.
brain: The center of thought and emotion in the central nervous system. The brain is responsible for the coordination and control of body activities and the interpretation of information from inside and outside the body.
cell body: In neurons, the main part of the cell around the nucleus excluding long processes such as axons and dendrites.
central nervous system (CNS): One of the two major divisions of the nervous system. The CNS consists of the brain and spinal cord.
cognitive function: The mental process of knowing, thinking, learning, and judging.
dendrite: A branching outgrowth of a neuron that carries information, in the form of a nerve impulse, into the cell body of the neuron. Each nerve usually has many dendrites.
glial cells (glia): Specialized cells that surround neurons. They provide mechanical and physical support to neurons and electrical insulation between neurons.
interneuron: A type of neuron that connects only with other neurons and thus delivers information only between neurons.
involuntary response: A nervous system response, such as a reflex, that is not under the control of the brain, and thus does not involve choice.
learning: The acquisition of knowledge or skill. It occurs in, and may lead to changes in, the brain.
motor neuron: A neuron that delivers information from a sensory neuron or interneuron to muscles or glands in the body in order to produce a response.
motor output: The body’s response to motor information delivered through motor neurons.
myelin: The insulating sheath that surrounds axons.
nerve: A bundle of neurons bound together by a protective sheath of connective tissue.
nerve impulse: Information in the form of an electrochemical signal that travels through a neuron in response to a stimulus.
nervous system: The entire, integrated system of nerve tissue in the body. It is composed of the brain, spinal cord, nerves, and glia. The human nervous system can be subdivided into the central nervous system (CNS) and the peripheral nervous system (PNS).
neural pathway: An interconnected set of neurons that delivers information (in the form of a nerve impulse) related to a body function.
neural signaling: The delivery of information through a neural pathway.
neuron: A specialized cell that delivers information within the body.
paralysis: Loss or impairment of motor function due to damage of the nervous system by injury or disease. Paralysis below the waist only is referred to as paraplegia; complete paralysis below the neck is referred to as quadriplegia.
peripheral nervous system (PNS): One of the two major divisions of the nervous system. Nerves in the PNS connect the central nervous system (CNS) with sensory organs, other organs, muscles, blood vessels, and glands.
plasticity: The ability of the brain to change through the formation or strengthening of connections between neurons in the brain.
positron emission tomography (PET): A technique for imaging the brain in action. PET images show active regions in the brain.
postsynaptic cell: A neuron that receives a nerve impulse across a synapse.
presynaptic cell: A neuron that sends a nerve impulse across a synapse.
reflex: A type of involuntary response.
sensory input: Information received by the body through sensory organs, such as the eyes, ears, nose, and skin.
sensory neuron: A neuron that delivers sensory information from the sensory organs to interneurons or motor neurons.
spinal cord: The part of the central nervous system that is located inside the vertebral column. Neurons in the spinal cord connect neurons in the brain to neurons in the body.
stimulus: Any information coming into the body that is capable of generating a nerve impulse.
synapse: The space separating the axon terminals of a neuron from the dendrites of the next neuron in a neural pathway.
traumatic brain injury (TBI): Injuries to the brain caused by physical trauma to the head.
vertebral column: The series of bones that extend from the skull to the tailbone. It provides support and forms a flexible, protective case for the spinal cord. The bones of the vertebral column are called vertebrae.
voluntary response: A nervous system response that is under control of the brain, and thus involves choice.