2. A rod consisting of cartilage running underneath, and supporting, the nerve cord.
3. In embryology, a rod-shaped body of cells that is the center of development of the axis of the skeleton.
4. A flexible rodlike structure that forms the main support of the body in all chordates (animals having a notochord, or dorsal stiffening rod) during some stage of their development.
In vertebrates, the notochord develops into a true backbone in the embryonic phase while primitive chordates; such as, lancelets and tunicates, keep a notochord throughout their existence.
2. Sclerosis of the posterior columns of the spinal cord, caused by infection of the central nervous system.
3. Slowly progressive degeneration of the spinal cord that occurs in the tertiary (third) phase of syphilis a decade or more after originally contracting the infection.
Among the terrible features of tabes dorsalis are lancinating lightning-like pain, ataxia (wobbliness), deterioration of the nerves to the eyes (the optic nerves) leading to blindness, urinary incontinence, loss of the sense of position, and degeneration of the joints.
Symptoms include: postural instability; especially, when the eyes are closed, and a staggering wide-base gait are characteristic of this disease; hence the name locomotor ataxia. Pain and paresthesias are common; especially, lightning pains, described as sharp, stabbing, and paroxysmal.
Ankle and knee reflexes are diminished or lost. Many symptoms characteristic of syphilis such as pupillary changes, optic atrophy, bladder disturbances, and development of trophic ulcers; especially, on the feet, make diagnosis certain.
The principal histologic changes are in the root entry zones of the posterior spinal nerve roots with consequential degeneration and atrophy of the posterior columns of the cord.
Still another description of tabes dorsalis with an updated perspective for clarification
Tabes dorsalis is a slow degeneration of the nerve cells and nerve fibers that carry sensory information to the brain.
The degenerating nerves are in the dorsal columns of the spinal cord (the portion closest to the back of the body) and carry information that help maintain a person's sense of position.
Tabes dorsalis is the result of an untreated syphilis infection. Symptoms may not appear for some decades after the initial infection and include weakness, diminished reflexes, unsteady gait, progressive degeneration of the joints, loss of coordination, episodes of intense pain and disturbed sensation, personality changes, dementia, deafness, visual impairment, and impaired response to light.
The disease is more frequent in males than in females. Onset is commonly during mid-life. The incidence of tabes dorsalis is rising, in part due to co-associated HIV infection.
If left untreated, tabes dorsalis can lead to paralysis, dementia, and blindness. Existing nerve damage cannot be reversed.