Central Nervous System Regeneration
Unlike peripheral nervous system injury, injury to the central nervous system is not followed by extensive regeneration. It is limited by the inhibitory influences of the glial and extracellular environment. The hostile, non-permissible growth environment is, in part, created by the migration of myelin-associated inhibitors, astrocytes, oligodendrocytes, oligodendrocyte precursors, and microglia. The environment within the CNS, especially following trauma, counteracts the repair of myelin and neurons. Growth factors are not expressed or re-expressed; for instance, the extracellular matrix is lacking laminins. Glial scars rapidly form, and the glia actually produce factors that inhibit remyelination and axon repair; for instance, NOGO and NI-35. The axons themselves also lose the potential for growth with age, due to a decrease in GAP 43 expression.
Slower degeneration of the distal segment than that which occurs in the peripheral nervous system also contributes to the inhibitory environment because inhibitory myelin and axonal debris are not cleared away as quickly. All these factors contribute to the formation of what is known as a glial scar, which axons cannot grow across. The proximal segment attempts to regenerate after injury, but its growth is hindered by the environment. It is important to note that central nervous system axons have been proven to regrow in permissible environments; therefore, the primary problem to central nervous system axonal regeneration is crossing or eliminating the inhibitory lesion site.
Read more about this topic: Neuroregeneration
Famous quotes containing the words central, nervous, system and/or regeneration:
“My solitaria
Are the meditations of a central mind.
I hear the motions of the spirit and the sound
Of what is secret becomes, for me, a voice
That is my own voice speaking in my ear.”
—Wallace Stevens (1879–1955)
“It is a bore, I admit, to be past seventy, for you are left for execution, and are daily expecting the death-warrant; but ... it is not anything very capital we quit. We are, at the close of life, only hurried away from stomach-aches, pains in the joints, from sleepless nights and unamusing days, from weakness, ugliness, and nervous tremors; but we shall all meet again in another planet, cured of all our defects.”
—Sydney Smith (1771–1845)
“The North American system only wants to consider the positive aspects of reality. Men and women are subjected from childhood to an inexorable process of adaptation; certain principles, contained in brief formulas are endlessly repeated by the press, the radio, the churches, and the schools, and by those kindly, sinister beings, the North American mothers and wives. A person imprisoned by these schemes is like a plant in a flowerpot too small for it: he cannot grow or mature.”
—Octavio Paz (b. 1914)
“The republic, as I at least understand it, means association, of which liberty is only an element, a necessary antecedent. It means association, a new philosophy of life, a divine Ideal that shall move the world, the only means of regeneration vouchsafed to the human race.”
—Giuseppe Mazzini (1805–1872)