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 occur when the normal foot arches have partially or completely collapsed. When the foot is put to the ground the inner or middle side of the foot comes down to the floor rather than remaining raised. This can cause the whole foot to roll inwards (this is called over-pronation).