Download Why dread a bump on the head? October 2014 Lesson 5: What

Why dread a bump on the head?
Lesson 5: What happens to neurons after TBI?
October 2014
APOPTOSIS
(Pronounced either ape-oh-toe-sis, ay-pop-toe-sis, or uh-pop-toe-sis)
What is it?
Apoptosis is a mode of “programmed cell death” in which the cell plays
an active role in modulating its own death. Apoptosis is controlled by
highly conserved genes in cells’ DNA and is initiated by the cell in
response to external and internal biochemical signals. In the case of TBI,
these signals, which prompt certain cells to undergo apoptosis, are
released by surrounding cells that are injured.
Process
When triggered, the apoptosis pathway leads to an organized
degradation of the cell involving the following steps:
1. The cell begins to shrink and become more rounded. The
cytoplasm of the cell becomes denser and the organelles begin
to break down and become tightly packed.
2. Inside the nucleus, the chromatin DNA begins to condense and
aggregate. An enzyme activated by the apoptotic pathway
breaks down the DNA by cutting it at very specified places. This
results in very regular DNA fragments that are 180 or multiples
of 180 (i.e. 360, 540 etc.) base pairs long each.
3. The nucleus then breaks into several discrete bodies called
chromatin bodies each containing condensed, systematically
fragmented chromatin DNA.
4. The whole cell breaks apart into circular components called
apoptotic bodies. These apoptotic bodies are enclosed inside
cellular membrane.
5. During the final stages of apoptosis, the dying cell displays a
molecule on its surface that marks the cell for removal. This
signal molecule is detected by another type of cell whose special
role is to engulf and remove the apoptotic cell. The removal of
apoptotic cells occurs in systematic way and does not elicit an
inflammatory response. However, inflammatory and other
immune responses can elicit apoptosis.
NECROSIS
What is it?
Necrosis is a form of cell death that occurs when factors external to the
cell such as trauma, injury, or infection cause damage to the cell.
Process
Necrosis is not a systematically modulated process and its course often
depends on the type of injury affecting the cell. However, necrosis does
involve some characteristic steps:
1. When damaged, the cell swells and begins to lose its integrity.
As a result, the cell becomes more amorphous in shape.
2. The chromatin DNA begins to condense and form dispersed
clumps throughout the nucleus.
3. The organelles of the cell begin to degrade.
4. The cell membrane continues to break down until, in the final
stages, the contents of the cell (cytoplasm, organelles,
chromatin etc.) spill out.
5. A necrotic cell does not display a biochemical signal for its quick
removal. Therefore, cell remnants and dead tissue can build up
and trigger an inflammatory response. Other specialized cells
then come in to engulf and clear away the necrotic cell debris.