Structure: < Click on image >


Motor Neurons. Nuclear groups in the cat sacral spinal cord (Nissl stain) shown at the left. A single motor neuron is shown at higher magnification at the right. The small cells around the motor neuron are glial cells: only their nuclei are stained. Note the dendrites, nucleus, nucleolus and Nissl substance (clumps of darkly stained RNA) in the cytoplasm and extruding a short distance into dendrites. A possible axon is at the lower right (devoid of Nissl substance). The spinal cord motor neurons are located in the anterior horn (gray). They are quite prominent, the cell bodies of some reaching 100 microns in diameter. The anterior horn motor neurons are commonly divided into a medial group and a lateral group, although these groups may have specific names at different segmental levels. The medial group is present throughout the cord and innervates axial musculature. A lateral group is added on in the cervical and lumbosacral enlargements and innervates the musculature of the extremities (arm and hand, and leg and foot).



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