Motor pool (neuroscience)
The size, composition, and anatomical location of each motor pool is tightly controlled by complex developmental pathways.
The cell bodies of motor neurons are located in the ventral horn of the spinal cord and the brainstem.
[1] Motor pools function primarily to integrate synaptic input from higher CNS centers into precise and consistent contraction patterns.
Further, this differential recruitment of motor neurons occurs in instances of both increasing and decreasing contraction strength.
Glial cell line-derived neurotrophic factor (GDNF) has been discovered to play an especially important role in all layers of motor pool development.
In the case of alpha- and gamma- differentiation, it has been shown that gamma motor neurons express significantly higher levels of certain GDNF receptor subunits.
[4] Alpha motor neurons are also grouped into subclasses based on the types of muscle fibers they target, which also determines their functional characteristics.
Due to their relatively small axonal diameter, neurons that target S type fibers require a smaller input current to reach threshold potential.
Conversely, the largest neurons, which target FF type fibers, require a greater input current to reach threshold.
Some researchers have speculated that the number of neurons within a given pool is determined by competitive interactions between different Hox genes.
The evolutionary analysis would predict an abnormally large motor pool innervating the muscle of the human tongue, relative to those of other mammals.
The evolutionary analysis also predicts large motor pools innervating the muscles of the human hand.
As Richard Young explains: It has been proposed that the hominid lineage began when a group of chimpanzee-like apes began to throw rocks and swing clubs at adversaries and that this behaviour yielded reproductive advantages for millions of years, driving natural selection for improved throwing and clubbing prowess.
Effective clubbing requires the recruitment of several motor units to produce a secure grip through impact.
These movements are governed by motor pools in the midbrain and in Onuf's nucleus in the lumbosacral spinal cord, respectively.
Currently, research is being conducted on these ALS-resistant motor pools, and their pool-specific molecular identities are being examined for potential neuroprotective qualities.
