Heel
Encyclopedia
In human anatomy, the heel is the prominence at the posterior end of the foot
. It is based on the projection of one bone, the calcaneus or heel bone, behind the articulation of the bones of the lower leg
.
to the ankle bone. Because the ankle bone is placed over the heel bone, these rays are adjacent near the toes but overriding near the heel, and together they form the arches of the foot
that are optimized to distributed compressive forces across an uneven terrain. In this context the heel thus forms the posterior point of support that together with the balls of the large and little toes bear the brunt of the loads.
To distribute the compressive forces exerted on the heel during gait
, and especially the stance phase when the heel contacts the ground, the sole of the foot is covered by a layer of subcutaneous connective tissue up to 2 cm thick (under the heel). This tissue has a system of pressure chambers that both acts as a shock absorber and stabilises the sole. Each of these chambers contains fibrofatty tissue covered by a layer of tough connective tissue made of collagen
fibers. These septa
("walls") are firmly attached both to the plantar aponeurosis above and the sole's skin
below. The sole of the foot is one of the most highly vascularized regions of the body surface, and the dense system of blood vessels further stabilize the septa.
The Achilles tendon
is the muscle tendon of the triceps surae
, a "three-headed" group of muscles -- the soleus
and the two heads of the gastrocnemius
. The main function of the triceps surae is plantar flexion, i.e. to stretch the foot downward. It is accompanied by a "fourth head", the slight plantaris muscle
, the long slender tendon of which is also attached to the heel bone but not visible.
), the heel is well above the ground at the apex of the angular joint known as the hock
. In plantigrade
species it rests on the ground. In birds, the heel is the backward-pointing joint which is often mistaken as the "knee
" (the actual knee of birds is hidden under the plumage).
Foot
The foot is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made up of one or more segments or bones, generally including claws...
. It is based on the projection of one bone, the calcaneus or heel bone, behind the articulation of the bones of the lower leg
Human leg
The human leg is the entire lower extremity or limb of the human body, including the foot, thigh and even the hip or gluteal region; however, the precise definition in human anatomy refers only to the section of the lower limb extending from the knee to the ankle.Legs are used for standing,...
.
Human anatomy
The compressive forces applied to the foot are distributed along five rays, three medial (side of big toe) and two lateral (side of little toe). The lateral rays stretch over the cuboid bone to the heel bone and the medial rays over the three cuneiform bones and the navicular boneNavicular bone
The navicular bone is a small bone found in the feet of both humans and horses.- Human anatomy :The navicular bone is one of the tarsal bones, found in the foot. Its name derives from the bone's resemblance to a small boat, caused by the strongly concave proximal articular surface...
to the ankle bone. Because the ankle bone is placed over the heel bone, these rays are adjacent near the toes but overriding near the heel, and together they form the arches of the foot
Arches of the foot
-External links:* * *...
that are optimized to distributed compressive forces across an uneven terrain. In this context the heel thus forms the posterior point of support that together with the balls of the large and little toes bear the brunt of the loads.
To distribute the compressive forces exerted on the heel during gait
Gait
Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency...
, and especially the stance phase when the heel contacts the ground, the sole of the foot is covered by a layer of subcutaneous connective tissue up to 2 cm thick (under the heel). This tissue has a system of pressure chambers that both acts as a shock absorber and stabilises the sole. Each of these chambers contains fibrofatty tissue covered by a layer of tough connective tissue made of collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
fibers. These septa
Septum
In anatomy, a septum is a wall, dividing a cavity or structure into smaller ones.-In human anatomy:...
("walls") are firmly attached both to the plantar aponeurosis above and the sole's skin
Dermis
The dermis is a layer of skin between the epidermis and subcutaneous tissues, and is composed of two layers, the papillary and reticular dermis...
below. The sole of the foot is one of the most highly vascularized regions of the body surface, and the dense system of blood vessels further stabilize the septa.
The Achilles tendon
Achilles tendon
The Achilles tendon , also known as the calcaneal tendon or the tendo calcaneus, is a tendon of the posterior leg. It serves to attach the plantaris, gastrocnemius and soleus muscles to the calcaneus bone.- Anatomy :The Achilles is the tendonous extension of 3 muscles in the lower leg:...
is the muscle tendon of the triceps surae
Triceps surae
The triceps surae is a pair of muscles located at the calf - the gastrocnemius and the soleus...
, a "three-headed" group of muscles -- the soleus
Soleus muscle
- References :* Gray, Henry. Pick, T. Pickering, & Howden, Robert . Gray's Anatomy . New York: Barnes & Noble Books.- External links :...
and the two heads of the gastrocnemius
Gastrocnemius muscle
In humans, the gastrocnemius muscle is a very powerful superficial pennate muscle that is in the back part of the lower leg. It runs from its two heads just above the knee to the heel, and is involved in standing, walking, running and jumping. Along with the soleus muscle it forms the calf muscle...
. The main function of the triceps surae is plantar flexion, i.e. to stretch the foot downward. It is accompanied by a "fourth head", the slight plantaris muscle
Plantaris muscle
Plantaris is a vestigial structure and one of the superficial muscles of the posterior crural compartment of the leg.It is innervated by the tibial nerve ....
, the long slender tendon of which is also attached to the heel bone but not visible.
Evolutionary variation
In the long-footed mammals, both the hoofed species (unguligrade) and the clawed forms which walk on the toes (digitigradeDigitigrade
A digitigrade is an animal that stands or walks on its digits, or toes. Digitigrades include walking birds , cats, dogs, and many other mammals, but not plantigrades or unguligrades...
), the heel is well above the ground at the apex of the angular joint known as the hock
Hock (zoology)
The hock, or gambrel, is the joint between the tarsal bones and tibia of a digitigrade or unguligrade quadrupedal mammal, such as a horse, cat, or dog...
. In plantigrade
Plantigrade
right|151px|thumb|Human skeleton, showing plantigrade habitIn terrestrial animals, plantigrade locomotion means walking with the podials and metatarsals flat on the ground. It is one of three forms of locomotion adopted by mammals...
species it rests on the ground. In birds, the heel is the backward-pointing joint which is often mistaken as the "knee
Knee
The knee joint joins the thigh with the leg and consists of two articulations: one between the fibula and tibia, and one between the femur and patella. It is the largest joint in the human body and is very complicated. The knee is a mobile trocho-ginglymus , which permits flexion and extension as...
" (the actual knee of birds is hidden under the plumage).
See also
- Achilles' heelAchilles' heelAn Achilles’ heel is a deadly weakness in spite of overall strength, that can actually or potentially lead to downfall. While the mythological origin refers to a physical vulnerability, metaphorical references to other attributes or qualities that can lead to downfall are common.- Origin :In Greek...
- Calcaneal spur
- Plantar fasciitisPlantar fasciitisPlantar fasciitis is a painful inflammatory process of the plantar fascia, the connective tissue on the sole of the foot.Longstanding cases of plantar fasciitis often demonstrate more degenerative changes than inflammatory changes, in which case they are termed plantar fasciosis. The suffix...
- High-heeled footwear