part of anterior spinal root BTO:0000865 BrendaTissueOBO The motor division of each spinal nerve, attached centrally to the spinal cord and joining peripherally with the corresponding posterior (sensory) root to form the nerve before it emerges through the intervertebral foramen. It conveys motor fibers to skeletal muscle and contains preganglionic autonomic fibers at thoracolumbar and sacral levels. There are 31 anterior and 31 posterior roots: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. Called also ventral or motor root of spinal nerve, root ventralis nervi spinalis, and root motoria nervi spinalis. anterior root of spinal nerve motor root of spinal nerve motor spinal root radix anterior nervi spinalis root motoria nervi spinalis root ventralis nervi spinalis ventral root of spinal nerve spinal root