Glossary of Terms

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Actin -  A filamentous protein that is a key component of the framework of the cell.
Allodynia -  A disorder in which sensations that normally do not hurt become painful.
Analgesic -  A class of drugs 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.
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.
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.
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 neuron, 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.
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.
Drosophila melanogaster -  A fruit fly often used in genetic studies.
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.
Excitotoxicity -  An abnormal stimulation or activation of neurons in the brain and spinal cord that result in cell death. This stimulation is attributed to excess amounts of the neurotransmitter, glutamate.
Free Radicals -  Highly unstable molecules, released by a spinal cord injury, which can quickly attack healthy cells. These molecules overwhelm the body’s antioxidants, which normally neutralize them, creating a damaging condition known as oxidative stress.
Gait -  The manner in which a human or animal walks.
Gangliosides -  Proteins that give the surface of a cell a negative charge and are thought to be involved in many different cell functions.
Gene Expression -  A term used to describe which genes are active in, or influence, a biologic process.
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.
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.
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. Interneurons are crucial determinants of many rhythmic motor behaviors.
Intracellular 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.
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 rehabilitation therapy that enables some people with spinal cord injuries to regain limited independent walking. The training involves supporting people over a treadmill while they are helped to make stepping motions.
Lumbar -  The low-level nervous structure of the spinal cord responsible for controlling the abdomen, hips, quadriceps, hamstrings, feet and ejaculation.
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 -  Tiny immune system scavenger cells that remove debris from the brain and spinal cord.
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.
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 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) are 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.
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, which promote axon regeneration almost like a nerve-cell fertilizer, 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, which 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.
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 Cells -  Cells that have the ability to divide for indefinite periods in culture and differentiate into multiple specialized cell types
Progenitor Cell -  Any type of cell that spawns other cells.
Proprioception -  Perception of movement and spatial orientation.
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.
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, similar to oligodendrocytes in the central nerve system, which wrap around axons to create a protective layer of myelin. 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 the groups 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.
Spasticity -  An increase in muscle tone with exaggerated tendon reflexes.
Stem Cells -  Self-renewing, primitive cells. When a stem cell divides, it creates another stem cell and a daughter cell that can become a mature cell in any organ in the body.
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.
Vectors -  Viruses that have been rendered harmless so they can be used to transport therapeutic genes into target cells.

Courtesy Christopher Reeve Foundation