The motor neurons of the spinal cord occupy, bilaterally, two columns, 40cm in length in the adult and 0.5mm in diameter. These form Lamina or nucleus 9th in the rexed nomenclature. Each column contains 200000 motor neurons with 150000 innervating skeletal muscles and 50000 innervating intrafusal muscles. The motor neurons show a range of diameters. Cell bodies with a range between 100 and 25 micrometers are classified as alpha-motor neurons.
Those with a diameter between 40 and 15 micrometers are gamma-motor neurons. It is possible that the population overlap represents beta-motor neurons. Within the anterior horn of the spinal cord the motor neurons have a distinct topographical localization. Motor neurons supplying the muscles of the neck and trunk are located medially, whereas those supplying the muscles of the limbs have a lateral location. The cervical and lumbar enlargements of…
