This glossary is designed to help you as you learn more about spinal repair research. You may want to bookmark this page for easy reference.

A-C,  D-F,  G-I,  L-M,  N-O,  P-R,   S-Z

Actin
A filamentous protein that is a key component of the framework of a cell.

Allodynia
A disorder in which sensations that normally do not hurt become painful.

Analgesic
A class of drug that relieves pain without causing loss of consciousness.

Apoptosis
Programmed cell death, or cell suicide, which is part of the natural life cycle of a cell. Apoptosis can be triggered by age, injury, or unknown factors. When the cell senses that it's not healthy, it goes through a series of changes, finally chopping its DNA and proteins into small packets that are cleaned up by microglia.

Astrocytes
Cells that nourish and support spinal neurons.

Autonomic Dysreflexia
A potentially fatal complication of spinal cord injuries that involves episodes of extreme hypertension and sometimes leads to intracranial hemorrhage or stroke.  It occurs in 90% of people with cervical or high thoracic cord injuries.

Axon
The long tail of a neuron that transmits electrical impulses from the cell body.

Axonal Transport
The mechanism that enables neurons to send proteins and chemical messages back and forth along axons.

C.Elegans
Caenorhabditis elegans is a small (1 mm. long) soil roundworm found in temperate regions. It is an ideal model organism to study because, from a molecular point of view, it shares many essential characteristics (i.e., genes) with humans.

CA2+ -permeable AMPA Receptors
Receptors that act like gatekeepers. When activated by glutamate, they open channels in the cell membrane that permit calcium to enter. Excess glutamate from injured cells may cause the receptors of neighboring cells to admit toxic levels of calcium.

Calcium Channels
Tiny channels in the cell membrane that permit calcium to pass into or out of the cell. They also trigger intracellular actions, including the release of neurotransmitters, when the cells are stimulated by sensory or other input

Catecholamines
Chemicals produced by organs that are controlled by the sympathetic nervous system.  These substances are involved in the fight-or-flight response to stress.

Cell Adhesion Molecules (CAMs)
Proteins that adhere to the surface of an elogating axon and direct it to its final address in the brain or spinal cord.

Central Nervous System
The brain and spinal cord.

Central Pattern Generator (CPG)
A network of spinal neurons that, when stimulated by neurotransmitters, cause the muscles of the legs to move in rhythmic stepping motions.

Cervical
The high-level nervous structure of the spinal cord responsible for controlling the neck muscles, diaphragm, shoulders, wrists, triceps, and fingers.

Chondroitin Sulfate Proteoglycans
Molecules that are a major component of the scar that forms at the site of a spinal cord injury and inhibit axon regeneration. They may act on their own or, because of their large size and negative charge, may attract other growth inhibitors to the lesion - or both.

Collateral Sprouting - see Nerve SproutingComplement System.
A mechanism that amplifies the inflammatory response and produces molecules that either are toxic or recruit and activate other immune cells to produce toxins. More than thirty blood proteins comprise this system, which is activated by injured cells and tissues.

Cortocospinal Tract
A nerve circuit pathway that originates in the brain's cerebral cortex and extends to lower levels of the cord, where descending axons send electrical impulses to the spinal motor neurons that, in turn, control the muscles.

Cyclic AMP
A signaling molecule

Cytokines
Messenger molecules that enable immune cells to "talk" to one another and to other cells. Cytokines regulate the strength and duration of an immune response. Neurons also use certain cytokines to communicate with each other. Common cytokines include interferon, interlukin, and lymphokines.

Cytoskeleton
A self-renewing support structure that enables cells, including neurons, to move and maintain their proper shape and size.

Demyelination
A cellular response to trauma that destroys myelin, the fatty substance that insulates and protects axons to improve their transmission of electrical impulses. Demyelination impedes or halts that transmission, resulting in a loss of function.

Dendrite
The branching fibers of a neuron that receive electrical impulses from other neurons' axons and transmit the signals towards the cell body.

Dorsal Root Ganglion (DRG) Neurons
Neurons just outside the spinal cord that receive sensory information from the periphery of the body and transmit it to the brain. These cells readily regenerate their axons after an injury.

Dorsal Horns (also called posterior horns)
A pair of projections that form the back "wings" of the butterfly-shaped gray matter in the spinal cord.

Dorsal Root Ganglion (DRG) Neurons
Neurons just outside the spinal cord that receive sensory information from the periphery of the body and transmit it to the brain. These cells readily regenerate their axons after an injury.

Dorsal Spinal Cord
The side of the spinal column closest to the upper surface or the back of an animal.

Draper
A molecule on the surface of glial cells that seems to be involved in identifying injured neurons and driving their elimination.

Drosophila Melanogaster
A fruit fly, often used in genetic studies, whose well-defined nerves are very similar to those in humans.

Elastase
An enzyme that breaks down proteins, it sometimes acts as damaging protein that kills neurons by disrupting their blood supply.

Electrophysiology
Monitoring and describing the electrical activity of cells.

Embryonic Stem Cells
Very primitive cells that develop within days of ova fertilization with the potential to develop into all of the body's cell types.

Extracellular Matrix
The filamentous material surrounding cells. It contains nourishment for cells as well as molecules that tell them what to do, including some that guide growing axons.

Free Radicals
Highly unstable molecules released by a spinal cord injury that can quickly attack healthy cells. These molecules overwhelm the body's antioxidants, which normally neutralize them, creating a damaging condition known as oxidative stress.

GABA (Gamma-aminobutyric acid)
The most abundant inhibitory neurotransmitter in the spinal cord.

Gait
The manner in which a human or animal walks.

Gabapentin
An anti-convulsive drug that may be useful in treating the chronic pain that commonly afflicts people with spinal cord injuries.

Gangliosides
Proteins that give the surface of a cell a negative charge and are thought to be involved in many different cell functions.

Gap Junctions
Very narrow channels between cells that permit cell-to-cell communications.

Gene
A segment of DNA located in a specific site on a chromosome that directs the formation of an enzyme or other protein.

Gene Expression
A term used to describe which genes are active in, or influence, a biologic process.

Gene Therapy
Any therapy that aims to cure or prevent disease by replacing, repairing, or supplementing a defective gene.

Genome
The complete set of genes in an organism.

Glia (also neuroglia)
Nerve-helper cells that provide structural support, nourishment, and protection for neurons.  Members of the glia family are oligodendrocytes (oligodendria), astroglia cells (astrocytes), ependymal cells, and microglia cells. Glia form scar tissue at the site of a spinal cord injury and pose both a physical and - because they produce several types of growth-inhibiting molecules - a chemical barrier to regenerating axons.

Glial Scar
Non-viable nerve tissue composed of glial cells that form a barrier to nerve regrowth after spinal cord trauma has occurred.

Gliosis
The process of scar formation after a spinal cord injury. Gliosis clears dead tissue and walls off the damaged region to prevent aberrant nerve cell activity, but it also inhibits the survival of neighboring cells. The resultant scar poses both a physical and chemical barrier to nerve cell regeneration.

Grey Matter
The part of the spinal cord and brain consisting mainly of cell bodies and dendrites and few myelinated axons.

Growth Cone
The leading tip of a growing axon. It is highly responsive to growth factors and guidance molecules.

Guidance Molecules
Proteins that push and pull the axons of embryonic nerve cells toward their target connections.

Hypoxia
A condition in which cells are deprived of oxygen.

Interleukin-10 (IL-10)
A naturally occurring, potent anti-inflammatory. nerve-cell protector.

Interneurons
The most abundant type of neuron in the central nervous system. They are the "middlemen" of nerve circuitry that connect only to other neurons, not to sensory cells or muscles, and help transmit nerve impulses. These cells are crucial to many rhythmic movement patterns, including walking.

L1
A surface, or cell adhesion, protein with that encourages the regrowth of nerve fibers.

Ligands
Messenger molecules that bind to and activate receptors on the surface of cells, which then change the behavior of the cell.

Locomotor Training
A rehabilitative therapy for people with spinal cord injury and some other neurological disorders. The training may lead to the recovery of some independent walking and improvements in overall health. Benefits include improved cardiovascular function, increased bone density, decreased spasticity, fewer pressure sores, and less glucose intolerance.

Lumbar
The low-level nervous structure of the spinal cord responsible for controlling the abdomen, hips, quadriceps, hamstrings, feet, and ejaculation.

MAG (myelin-associated glycoprotein)
A protein found in myelin that has powerful anti-growth properties that keep axons from regenerating

Messenger RNA (mRNA)
An exact copy of a cell's DNA that transmits instructions from the cell nucleus to the body of the cell where proteins are produced.

Methylprednisolone
A powerful steroid administered in the hours immediately after a spinal cord injury to limit harmful inflammation. It is the only approved treatment for acute spinal cord injury.

Microglia
The immune scavenger cells of the brain and spinal cord that are among the first responders that flock to the site of an injury to remove debris.

Midline
1) A line of cells running from top to bottom down the center of an embryo.  2) An imaginary line dividing the left and right halves of the body.

Motoneurons
Nerve cells that control the muscles.

Myelin
A fatty substance, produced by cells in the central nervous system known as oligodendrocytes. Myelin forms a protective sleeve around axons that enables them to conduct electrical impulses.

Necrosis
Cell death resulting from irreversible damage. Necrosis is a messy process compared to apoptosis. The dying cell swells and virtually explodes, spewing its contents and sending many damage messages to neighboring cells, which may then commit suicide. The byproducts of necrosis are not easily removed by scavenger cells, so scar tissue forms.

Nerve Sprouting
A condition following spinal cord trauma that results in the axon reconnecting to an inappropriate target. Synaptic conduction is restored but the pathway does not result in restoration of function.

Netrins
Molecules that attract and repel developing axons and appear to govern the direction in which they travel.

Neural Progenitors
Parent cells that give rise to each of the types of nerve cells.

Neurogenesis
The birth of neurons.

Neurons (nerve cells)
The basic unit of the nervous system. Neurons come in assorted shapes and sizes, and each type has a specific role. Chains of neurons transmit electrical impulses throughout the body.

Neuropathic Pain
Pain caused by disease in, or injury to, the nervous system.

Neurotransmission
The sending and receiving of electrical impulses through chains of neurons.

Neurotransmitters
The chemical messengers of the nervous system. They are released at the synapse (connection between nerve cells) and influence cell behavior. Common neurotransmitters include glutamate, serotonin, acetylcholine, and norepinephrine.

Neurotrophins
Molecules that are important in the development and maintenance of the nervous system. Neurotrophins promote axon regeneration almost like a nerve-cell fertilizer, and include nerve-growth factor (NGF), NT-3, BDNF, and NT 4/5.

Neutrophils
A type of white blood cell and one of the first immune cells to arrive during the acute inflammatory response to a spinal cord injury. Neutrophils manufacture enzymes that help kill bacteria, but in the brain and spinal cord, they are lethal to nerve cells.

Nogo
A powerful protein that occurs naturally in the spinal cord and prevents nerve cells from regenerating axons.

Nucleus
1) The organelle in eukaryotic cells that contains the majority of the cell's genetic material and is responsible for coordinating cellular growth and reproduction. 2) A mass of neural cell bodies in the brain or spinal cord, composed mainly of grey matter. Nuclei are usually hubs or transit points for signals within a neural subsystem (e.g., many of the different nerves that move the eyeballs gather together at the oculomotor nucleus).

Olfactory Ensheathing Glia (OEG)
Cells that support the sensory neurons lining the nasal cavity. When transplanted into the spinal cord, these cells may remyelinate damaged axons.

Oligodendrocytes
Cells that enwrap an axon with their flattened membranes to create an insulating layer of myelin.

Peripheral Nervous System
The network of nerves outside the brain and spinal cord. Unlike nerves in the central nervous system, peripheral nerves can regrow after an injury.

Plasticity
The ability of nerve circuitry to remodel itself.

Precursor Cell
A cell that has almost fully evolved into its final specialized form.

Progenitor Cell
A cell that has started to differentiate down a particular path but has not fully developed yet. Unlike stem cells, progenitors do not have the capacity to create indefinitely self-renewing copies of themselves. They evolve into a final, specialized cell type and cannot go back to being stem cells.

Proteases
Enzymes, or proteins, that break up other proteins. They are sometimes associated with cell death.

Receptors
Millions of protein molecules, posted like sentinels around a cell membrane, to screen the environment for messages addressed to them. Receptors are highly selective, usually responding to only one type of directive. The meeting of a messenger molecule, or ligand, with its receptor initiates a reaction inside the cell that ultimately affects what the cell does.

RhoA
A protein that regulates the structure of cells and causes regenerating axons to retract.

Robo (or Roundabout)
A signal molecule that influences the growth of neurons. It appears to send a “halt” message, stopping neurons from crossing the midline of the developing spinal cord.

Rubrospinal Tract
One of the major descending nerve pathways from the brain to the spinal cord.

Schwann Cells
Non-nerve cells in the peripheral nervous system that wrap around axons to create a protective layer of myelin, similar to oligodendrocytes in the central nervous system. They also may promote nerve regeneration following an injury.

Semaphorins
A family of proteins that play a role during axonal development. Semaphorins may inhibit axon growth or help growing axons find their way to their target connections - or both.  These proteins act like traffic cops, telling growing axons where they can and cannot go so that they reach their destinations.

Serotonin
One of a group of chemical messengers known as neurotransmitters that carries out communications in the brain and the body. This molecular messenger travels from neuron to neuron eliciting cellular responses that shape emotions and judgment.

SLPI (Secretory Leukocyte Protease Inhibitor)
Anti-bacterial protein that is abundant in saliva.

Slit
A protein that repels growing axons from the midline during embryonic development.

Soleus
The flat, broad calf muscle responsible for flexion of the ankle joint, particularly when the leg is bent at the knee.

Somatosensory Areas of the Brain
Portions of the brain that deal with bodily sensations.

Spasticity
An increase in muscle tone with exaggerated tendon reflexes.

Shark
A molecule that binds to the portion of Draper (see definiation above) that lies within the cell and probably enables Draper to transmit the, "I've-found-an- injured-neuron" signal.

Stem Cells
Primitive, unspecialized cells that have the capacity to divide for indefinite periods in culture. They have the potential to produce both new stem cells and differentiated, specialized cells. Embryonic stem cells are 'totipotent,' meaning that they can give rise to all the different cell types in the human body. Other types of stem cells spawn only a subset of tissue types.

Sympathetic Nervous System
Controls involuntary functions of the body, such as heart rate and blood pressure.

Synapse
The connection between two neurons that enables them to communicate. Synapses enable nerve impulses to travel through chains of neurons.

Synaptic Adhesion Molecules (SAMs)
Molecules that establish the first contact between two neurons, holding the cell membranes in place while their connection, or synapse, forms.

Synaptogenesis
The process of forming a nerve-to-nerve junction or synapse. After the formation of the synapse is complete, the signal is relayed by the release of a chemical transmitter from one membrane that binds to a receptor in the second membrane.

T-cells
White blood cells that are part of the immune system.

Tactile Allodynia
A condition in spinal cord injured individuals where pain is brought on by stimuli that would not cause pain in healthy individuals.

Two-photon Excitation Microscopy
A magnification technique that allows scientists to see the cells of living tissue up to one millimeter beneath the surface.

Vectors
Viruses that have been rendered harmless so they can be used to transport therapeutic genes into target cells.

White Matter
The part of the brain and spinal cord consisting mostly of myelinated axons.