The sole is the bottom of the foot
In humans the sole of the foot is anatomically referred to as the plantar aspect
The glabrous skin
on the sole of the foot lacks the hair
found elsewhere on the body, and it has a high concentration of sweat 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 during the early stages of embryonic development
. Like those of the palm
, the sweat pores of the sole lack sebaceous glands
The sole is a sensory organ by which we can perceive the ground while standing and walking. The subcutaneous tissue
in the sole has adapted to deal with the high local compressive forces on the heel
and the ball
(between the toes and the arch
) by developing a system of "pressure chambers." Each chamber is composed of internal fibrofatty tissue covered by external collagen
connective tissue. The septa
(internal walls) of these chambers are permeated by numerous blood vessel
s, making the sole one of the most vascularized
, or blood-enriched, regions in the human body.
The sole and the longitudinal arch of the foot
are supported by a thick connective tissue
, the plantar fascia
. The central component of this tissue
extends to the supporting bones and gives two divisions–the medial component
and lateral component
; thus they define the boundaries of the three muscle compartments of the sole (see below).
The bones underlying the sole form the arch
of the foot. The arches might collapse later in life, resulting in flat feet
The intrinsic muscles in the sole are grouped in four layers:
In the first layer, the flexor digitorum brevis
is the large central muscle located immediately above the plantar aponeurosis. It flexes the second to fifth toes and is flanked by abductor hallucis
and abductor digiti minimi
In the second layer, the quadratus plantae
, located below flexor digitorum brevis, inserts into the tendon of flexor digitorum longus on which the lumbricals
In the third layer, the oblique head of adductor hallucis
joins the muscle's transversal head on the lateral side of the big toe. Medially to adductor hallucis are the two heads of flexor hallucis brevis
, deep to the tendon of flexor hallucis longus. The considerably smaller flexor digiti minimi brevis
on the lateral side can be mistaken for one of the interossei.
In the fourth layer. the dorsal
and plantar interossei
are located between and below the metatarsal bones and act as antagonists.
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.
The tendons of several extrinsic foot muscle reach the sole:
* The tendons of the deep foot flexors in the posterior compartment of the leg, tibialis posterior
, flexor digitorum longus
, and flexor hallucis longus
, passes behind the medial malleolus
into the sole.
* The tendon of fibularis longus
similarly passes behind the lateral malleolus into the sole.
The soles of the feet are extremely sensitive to touch
due to a high concentration of nerve endings
, with as many as 200,000 per sole. This makes them sensitive to surfaces that are walked on, ticklish
and some people find them to be erogenous zone
Medically, the soles are the site of the plantar reflex
, the testing of which can be painful due to the sole's sensitivity.
The deep fibular nerve
from the common 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 in foot drop
The plantar digital nerves
from the medial plantar nerve
provide sensory innervation to the skin of the plantar aspect of the toes, except the medial part of the big toe and the lateral part of the little toe and the motor innervation of the first lumbrical.
The proper plantar nerve
from the common plantar digital nerve provide 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.
and deep branches
of the lateral plantar nerve
from the tibial 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.
The medial plantar nerve
from the tibial 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.
The saphenous nerve
from the femoral nerve
provides sensory innervation to the medial side of the foot as well as the medial side of the leg. Likewise, the sural 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.
The tibial nerve
from the sciatic nerve
provides sensory innervation to the skin of the sole and toes, and the dorsal aspect of the toes. It provides motor innervation to plantaris
, tibialis posterior, flexor hallucis longus, flexor digitorum longus as well as posterior muscles in the leg.
Society and culture
The purpose of protecting the sole against uncomfortable and harmful impacts of the environment during locomotion initiated the general introduction of footwear
in early human history. The achieved protection of the susceptible soles provided for faster and considerably more efficient movement particularly in adverse environmental terrains as against walking or running in bare feet.
Forcing specific groups of people or singled out individuals to go barefoot, thus wilfully depriving them of any means of protection to the susceptible soles, has been used to mark them as slaves, prisoners or otherwise unfree in most civilized cultures. Another purpose of this measure is to make escape attempts or resistance more difficult and to use the sociocultural significance of uncovered soles and bare feet in general as a conspicuous sign of degradation in the public eye. Down to the present day prisoners are forced to walk on just their bare soles without the commonplace protection through footwear in several countries around the world (see article on "barefoot"
The sensitivity of the sole makes it an objective for sensual touch, tickling
or sexual stimulation
and also a target for means of corporal punishment
The beating of the soles of a person's bare feet (foot whipping
or "bastinado") with specific objects such as rods and canes has hereby served as a means of corporal punishment
in various civilizations to this day. The application of this measure is mostly found in prisons and similar institutions, such as schools and reformatories. It is also a common method of physical torture
In Thailand, Saudi Arabia, and some Muslim countries it is considered offensive to sit raising the leg so the uncovered sole of the foot is visible and therefore taboo
Terrestrial animals using their soles for locomotion are called plantigrade
s, 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 large part of the remaining sole is covered by thick, tight, and smooth skin almost without furrows.
s, the pattern intensity of the epidermal 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 of ape
s, in the sole, the density decreases and is comparable to other apes.
The sole is subject to many skin diseases.
* Gait (human)
* Human skeletal changes due to bipedalism