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| Sole | |
|---|---|
 Human soles | |
| Details | |
| Part of | Foot |
| Artery | Medial plantar,lateral plantar |
| Nerve | Medial plantar,lateral plantar |
| Identifiers | |
| Latin | planta |
| TA98 | A01.1.00.044 |
| TA2 | 337 |
| FMA | 25000 |
| Anatomical terminology | |
In humans, thesole of thefoot is anatomically referred to as theplantar aspect.
Theglabrous skin on the sole of the foot lacks thehair andpigmentation found elsewhere on the body, and it has a high concentration ofsweat pores. The sole contains the thickest layers of skin on the body due to the weight that is continually placed on it. It is crossed by a set of creases that form duringthe early stages of embryonic development. Like those of thepalm, the sweat pores of the sole lacksebaceous glands.[medical citation needed]
The sole is a sensory organ by which the ground can be perceived while standing and walking. Thesubcutaneous tissue in the sole has adapted to deal with the high local compressive forces on theheel and theball (between the toes and thearch) by developing a system of "pressure chambers." Each chamber is composed of internal fibrofatty tissue covered by externalcollagen connective tissue. Thesepta (internal walls) of these chambers are permeated by numerousblood vessels, making the sole one of the mostvascularized, or blood-enriched, regions in the human body.[1]
The sole and thelongitudinal arches of the foot are supported by athick connective tissue, theplantar fascia. Thecentral component of this tissue extends to the supporting bones and gives two divisions–themedial component andlateral component; thus they define the boundaries of the three muscle compartments of the sole (see below).[2]
The bones underlying the sole form thearch of the foot. The arches might collapse later in life, resulting inflat feet.
The intrinsic muscles in the sole are grouped in four layers:
In the first layer, theflexor digitorum brevis is the large central muscle located immediately above the plantar aponeurosis. It flexes the second to fifth toes and is flanked byabductor hallucis andabductor digiti minimi.[2]
In the second layer, thequadratus plantae, located below flexor digitorum brevis, inserts into the tendon of flexor digitorum longus on which thelumbricals originate.[2]
In the third layer, the oblique head ofadductor hallucis joins the muscle's transversal head on the lateral side of the big toe. Medially to adductor hallucis are the two heads offlexor hallucis brevis, deep to the tendon of flexor hallucis longus. The considerably smallerflexor digiti minimi brevis on the lateral side can be mistaken for one of the interossei.[2]
In the fourth layer, thedorsal andplantar interossei are located between and below the metatarsal bones and act as antagonists.[2]
The central compartment is shared by the lumbricals, quadratus plantae, flexor digitorum brevis, and adductor hallucis; the medial compartment by abductor hallucis, flexor hallucis brevis, abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi (often considered part of the former muscle); whilst the lateral compartment is occupied by extensor digitorum brevis and extensor hallucis brevis.[3]
The tendons of several extrinsic foot muscle reach the sole:
The soles of the feet are extremely sensitive totouch due to a high concentration ofnerve endings, with as many as 200,000 per sole.[5] This makes them sensitive to surfaces that are walked on,ticklish and some people find them to beerogenous zones.[6]
Medically, the soles are the site of theplantar reflex, the testing of which can be painful due to the sole's sensitivity.
Thedeep fibular nerve from thecommon fibular nerve provides the sensory innervation of the skin between the first and second toes and the motor innervation of the muscles of the anterior compartment of the leg and dorsal foot. Damage to the deep fibular nerve can result infoot drop.[7]
Theplantar digital nerves from themedial plantar nerve provide sensory innervation to the skin of the plantar aspect of the toes, except for the medial part of the big toe and the lateral part of the little toe and the motor innervation of the first lumbrical.[7]
Theproper plantar nerve from the common plantar digital nerve provides sensory innervation to the plantar surface of the toes as well as the dorsal aspect of the distal interphalangeal phalanges. It also provides motor innervation to flexor hallucis brevis.[7]
Thesuperficial anddeep branches of thelateral plantar nerve from thetibial nerve provide sensory innervation to the skin of the lateral side of the sole, to the fifth and half the fourth toes, and the nail bed of these toes. They also provide motor innervation to quadratus plantae, abductor digiti minimi, flexor digiti minimi brevis, lateral three lumbricals, adductor hallucis, and the dorsal and plantar interossei.[7]
Themedial plantar nerve from thetibial nerve provides sensory innervation to the skin of the medial side of the sole, the skin of the medial three and a half toes, and the nail beds of these toes. It also provides motor innervation to abductor hallucis, flexor hallucis brevis, flexor digitorum brevis, and the first lumbrical.[7]
Thesaphenous nerve from thefemoral nerve provides sensory innervation to the medial side of the foot as well as the medial side of the leg. Likewise, thesural nerve provides sensory innervation to the skin on the lateral side of the foot as well as the skin on the posterior aspect of the lower leg.[7]
Thetibial nerve from thesciatic nerve provides sensory innervation to the skin of the sole and toes, and the dorsal aspect of the toes. It provides motor innervation toplantaris, tibialis posterior, flexor hallucis longus, flexor digitorum longus as well as posterior muscles in the leg.[7]
In Thailand, Saudi Arabia, and some Muslim countries, it is considered offensive andtaboo to sit raising the leg so the uncovered sole of the foot is visible.[8] Among societies that practicedhuman cannibalism in various parts of the world, the soles of the feet were considered among the best parts of the body to eat.[9] Soles may also be the subject offoot fetishism.[10]
Terrestrial animals using their soles for locomotion are calledplantigrade.
Inchimpanzees, the soles are furrowed with creases deeper and more distinct than in their palms. In the palms, the pattern density is thickest in the central part, but in the sole, the density is thickest near the big toe whilst a large part of the remaining sole is covered by thick, tight, and smooth skin almost without furrows.[11]
Inbonobos, the pattern intensity of theepidermal ridges (i.e. "fingerprints") of the palms and soles is considerably higher than in chimpanzees. Whilst the pattern intensity in the palm is the highest of all species ofapes, in the sole, the density decreases and is comparable to other apes.[12]
