involuntary actions and innervates smooth and cardiac muscles and glandular tissues.

Axon

Long nerve cell fibers that arise from a neuron’s cell body and that conduct electrical impulses to the target cell. Axons contact other nerve, muscle, and gland cells at synapses and release neurotransmitters that influence those cells.

Axonal transport

The process by which nerve cells move substances from the cell body down the axon and from the end of the axon back to the cell body. Transport down the axon is necessary because axons cannot synthesize many substances, such as proteins, that they need. Transport back to the cell body recycles substances and also carries signals taken up by axon terminals, such as trophic factors, to the cell body, where they can affect cellular processes.

Blood-brain barrier

Tight junctions are formed by endothelial cells that line blood vessels and regulate the entry of circulating substances and immune cells into the brain and spinal cord. Trauma may compromise these barriers and contribute to further damage in the brain and spinal cord. These barriers also prevent the entry of some potentially therapeutic drugs.

Brain-derived neurotrophic factor (BDNF)

Exogenous neurotrophic factor.

Cell adhesion molecules

Molecules on the outside surfaces of cells that bind to other cells or to the extracellular matrix (the material surrounding cells). Cell adhesion molecules influence many important functions, such as the entry of immune cells into the damaged spinal cord and the path finding of growing axons.

Central nervous system (CNS)

The portion of the nervous system that consists of the brain and spinal cord. The CNS coordinates the entire nervous system and is responsible for receiving sensory information from the environment and responding using motor impulses.

Central pattern generator (CPG)

A complex circuit of neurons responsible for coordinated rhythmic muscle activity, such as locomotion.

Clinical trials

Systematic studies with human patients aimed at determining the safety and effectiveness of new or unproven therapies. Systematic testing in clinical trials has four phases. Phase I trials determine both the safety of a drug or intervention and the appropriate dosage. Phase II trials, which are performed with relatively small groups of patients, establish efficacy and evaluate reported side effects. Phase III trials, which usually require much larger numbers of patients, compare the new therapies to established therapies or a placebo, or both, and continue to monitor the participants for adverse side effects. Phase IV trials are required by the FDA for additional analysis of postmarking, long-term risks, and benefits.