Following a brain injury, neurons adjacent to the damaged area may take over the functions performed by the damaged neurons in a process called collateral sprouting.
Neurons A, B and C before damage
****
**** **** ooo
* * oooo oooo
* * o o
* A * -- Soma -- o o
* * o o
* * o B o
* * o o
**** **** o o
******** oooo oooo
***** oooooo
**** oo
** -- Axons -- oo
*** o
** o
* ooooo
** oo oooo
** oo oo
** oo oo
**** ***** oo
* ************ oo
** oo ** oo
Telodendrons ---- * o ** o
* oo ** oo
** o ** o
** oo * o
* @@@@@@ * o
** @@@@ @@@@* oo
@@ @@ o
@ @ ooo
@ C @oooooo
@ @
@@ @@
@@@@ @@@@
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Collateral sprouting after damage
to neuron A
****
***** *****
*** *** ooo
* ** oooo oooo
** A * o o
** * o o
* ** o B o
* ** o o
***** ****** o o
******** o o
**** * oooo oooo
** * oooooo
** oo
** oo
** o
* o
ooooo
oo oooo
oo oo
oo oo
ooo ooo
oooooo oo oo
oooo oo oo oo
oo o oo o
New telodendrons -- oo oo oo oo
oo o oo o
oo oo oo o
oo @@@@@@ o o
oo @@@@ @@@@o oo
@@ @@ o
@ @ ooo
@ C @oooooo
@ @
@@ @@
@@@@ @@@@
@@@@@@
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@
@
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Following damage to neuron A, neuron B generates new telodendrons from its axon to form a synapse at the receptor sites on neuron C formerly occupied by neuron A.
Types of collateral sprouting:
Heterotypic collateral sprouting (aka reactive synaptogenesis): This type of collateral sprouting occurs within day and does not lead to recovery of function.
Homotypic collateral sprouting: Begins to occur after about four weeks and leads to recovery of function.
Although collateral sprouting does occur in the Central Nervous System, the damaged is often too extensive for it to have much effect. It is believed that collateral sprouting may also be one of the mechanisms behind associative learning/classical conditioning.
See also: Neurogenesis, Neuroplasticity
Sources:
Klein, Stephen B. Biological Psychology. Prentice Hall, New Jersey: 2000.
http://www.medinfo.ufl.edu/other/profmed/slides/pm011399/slide19.html
http://www.nyu.edu/classes/azmitia/lectures/lecture13/
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