The term "Somatic efference" refers to the peripheral nervous system and refers to the outflow of nerve signals from the CNS to the striated skeletal muscle.
There are two types of somatically effective nerve cell types:
(a) alpha-motor neurons, which directly affect the long and coarse extrafusal muscle cells which run from the tendon of origin of a muscle to its attachment tendon and are responsible for the development of the muscle's force
b) gamma-motor neurons, which directly affect the short and thin so-called intrafusal muscle cells which bundled 5 - 15 pcs. forms a so-called muscle spindle.
The muscle spindle is a kind of sensory organ that measures how much and how fast a muscle changes its length during a movement. The gamma motor neuron regulates the sensitivity of the muscle spindle.