Nerve fiber = multicellular, containing both an axon and surrounding myelin sheath. The axon comes from a single neuron, but the myelin sheath is made by a train of many myelinating Schwann cells. In the case of unmyelinated axons, the unmyelinated fiber shares each Schwann cell with several other unmyelinated axons.
Flat feet (pes planus) occur when a child has no arch in their foot. Because an arch does not form, the foot appears to turn to the outside. Children with out-toeing due to flatfeet will rarely experience pain symptoms will not require treatment.
Flat feet in adults can arise from a variety of causes. Here are the most common: 1  An abnormality that is present from birth. 2  Stretched or torn tendons. 3  Damage or inflammation of the posterior tibial tendon (PTT), which connects from your lower leg, along your ankle and to the middle of the arch.