Myeloid cells originate in bone marrow or spinal cord, or a resemblance to the marrow or spinal cord.For example, myeloid leukemia is leukemia that arises from abnormal growth in the blood-forming tissue of the bone marrow.This term should not be confused with  myelin , which is an insulating layer covering the axons of many neurons.or example, myeloid leukemia is leukemia that arises from abnormal growth in the blood-forming tissue of the bone marrow. This term should not be confused with  myelin , which is an insulating layer covering the axons of many neurons.