The lateral plantar nerve is a nerve of the sole of the foot. Originating from the sciatic nerve, which runs down the back of the leg, and below from the tibial nerve, which splits off from the sciatic, the lateral plantar serves the skin and muscles of the outer foot. This nerve gives sensation to the pinky toe and the outside of the fourth toe. It also sends motor signals to the abductor digiti minimi and the quadratus plantae muscles, which spread the little toe outward and curl the toes downward, respectively.
As both a sensory and a motor nerve, the lateral plantar nerve transmits electrical signals in both directions between the central nervous system (CNS) — the brain and spinal cord — and the foot. Sensory information felt by the outer toes, such as pain and pressure, are sent up the lateral plantar, through the tibial nerve, and up the sciatic toward the CNS. Traveling in the opposite direction are motor signals from the brain telling the muscles served by the lateral plantar nerve to contract.
The lateral plantar nerve is a division of the tibial nerve, which runs behind the knee and straight down the middle of the calf after branching off of the sciatic nerve in the lower posterior thigh. It originates behind the medial malleolus of the tibia, the large rounded bump at the base of the tibia bone that can be felt at the inside of the ankle, where the tibial nerve divides into its medial and lateral branches. In other words, the lateral plantar nerve begins along the inside aspect of the heel and crosses the underside of the foot diagonally, angling toward the pinky toe.
This nerve also has two branches: a deep and superficial branch. The superficial branch lies closer to the surface of the foot, penetrating the skin of the fifth toe and the outer half of the fourth as well as the far end of the abductor digiti minimi muscle just below the toe. It picks up information from sensory receptors in the skin about pressure, temperature, or pain and delivers it in the form of an electrical signal back to the CNS, while its motor portion sends a similar signal to the muscle that instructs it to fire and spread the little toe outward.
The deep branch, which as its name suggests is more internal to the foot, innervates the lateral aspect of the quadratus plantae, a deep muscle of the sole of the foot. This muscle assists in flexion or curling of the farthest toe joint, the distal interphalangeal joint. The deep branch of the lateral plantar nerve causes this action by delivering motor signals to this muscle. The lateral plantar also sends motor signals to both muscles ahead of its division into deep and superficial branches.