The plantaris is one of the superficial

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

s of the superficial posterior compartment of the leg, one of the fascial compartments of the leg. It is composed of a thin muscle belly and a long thin

tendon A tendon or sinew is a tough band of fibrous connective tissue, dense fibrous connective tissue that connects skeletal muscle, muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tensi ...

. While not as thick as the

achilles tendon The Achilles tendon or heel cord, also known as the calcaneal tendon, is a tendon at the back of the lower leg, and is the thickest in the human body. It serves to attach the plantaris, gastrocnemius (calf) and soleus muscles to the calcane ...

, the plantaris tendon (which tends to be between in length) is the longest tendon in the

human body The human body is the entire structure of a Human, human being. It is composed of many different types of Cell (biology), cells that together create Tissue (biology), tissues and subsequently Organ (biology), organs and then Organ system, org ...

. Not including the tendon, the plantaris muscle is approximately long and is absent in 8-12% of the population. It is one of the plantar flexors in the posterior compartment of the leg, along with the gastrocnemius and soleus muscles. The plantaris is considered to have become an unimportant muscle when human ancestors switched from climbing trees to bipedalism and in anatomically modern humans it mainly acts with the gastrocnemius.

Structure

The plantaris muscle arises from the inferior part of the lateral supracondylar ridge of the

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

at a position slightly superior to the origin of the lateral head of gastrocnemius. It passes posterior to the

knee joint In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the ...

in an inferomedial direction and becomes tendinous distally to insert into the

Achilles tendon The Achilles tendon or heel cord, also known as the calcaneal tendon, is a tendon at the back of the lower leg, and is the thickest in the human body. It serves to attach the plantaris, gastrocnemius (calf) and soleus muscles to the calcane ...

. It occasionally separately inserts into the medial side of the calcaneus.

Innervation

The plantaris muscle is innervated by the tibial nerve, a branch of the sciatic nerve in the sacral plexus. Signaling for contraction begins in the

frontal lobe The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a Sulcus (neur ...

of the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

with the pre-central gyrus ( primary motor cortex). Upper motor neurons are stimulated and send a signal through the

internal capsule The internal capsule is a paired white matter structure, as a two-way nerve tract, tract, carrying afferent nerve fiber, ascending and efferent nerve fiber, descending axon, fibers, to and from the cerebral cortex. The internal capsule is situate ...

and down the

corticospinal tract The corticospinal tract is a white matter motor pathway starting at the cerebral cortex that terminates on lower motor neurons and interneurons in the spinal cord, controlling movements of the limbs and trunk. There are more than one million neu ...

. Decussation of the lateral corticospinal tract occurs in the medullary pyramids, then the fibers continue down the contralateral side of the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

. Upper motor neurons synapse with lower motor neurons at the anterior horn of the spinal cord in the sacral plexus (formed from the anterior rami of spinal nerves L4, L5, S1–4). The lower motor neuron fibers continue down the sciatic nerve and then diverge into the tibial and common fibular nerves. The tibial nerve runs medially at the

. When the tibial nerve receives an action potential, the plantaris muscle contracts, providing weak plantar flexion of the foot and weak flexion of the knee.

Variation

The muscle may arise from the oblique popliteal ligament. Interdigitations with the lateral head of the gastrocnemius and a fibrous extension of the muscle to the patella are not unusual.

Function

The plantaris acts to weakly plantar flex the ankle joint and flex the

. The plantaris muscle may also provide proprioceptive feedback information to the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

regarding the position of the foot. The unusually high density of proprioceptive receptor end organs supports this notion.Moore, Keith L; & Dalley Arthur R (2008). ''Clinically Oriented Anatomy'' (6th ed.). Lippincott Williams and Wilkins. Its motor function is so minimal that its long tendon can readily be harvested for reconstruction elsewhere with little functional deficit. Often mistaken for a nerve by new medical students (and thus called the "freshman's nerve"), the muscle was useful to other

primate Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...

s for grasping with their feet.Andor, W.J.M., Glaudemans, Rudi A.J.O. Dierckx, Jan L.M.A. Gielen, Johannes (Hans) Zwerver (2015). ''Nuclear Medicine and Radiologic Imaging in Sports Injuries''. Springer. p. 762

Clinical significance

A common injury that is normally attributed to the plantaris muscle is a condition called ''tennis leg''. Although pain in the calf can be attributed to a rupture of the plantaris muscle, recent ultrasound research has shown that tennis leg more commonly arises from tears in the musculotendinous junction of the medial gastrocnemius. In one clinical study, 94 out of 141 patients (66.7%) diagnosed with tennis leg were found with a partial rupture of the gastrocnemius muscle, while rupture of the plantaris tendon was only seen in 2 patients (1.4%). Injury may occur from running, jumping, or pushing off one leg in sports such as tennis, basketball and soccer, which require quick foot movement in a certain direction. Isolated plantaris muscle strains are rare, and ruptures normally occur in conjunction with injury to other muscles in the posterior compartment of the lower leg. Symptoms of a plantaris muscle rupture may include an audible popping sound in the area during physical activity, swelling, pain in the back of the lower leg, and persistent soreness. Ankle flexion may also be painful.

Additional images

File:Plantaris muscle - animation.gif, Animation File:Sobo 1909 304.png, The plantaris is visible under the gastrocnemius. File:Plantaris muscle by Sanjoy Sanyal.webm, Dissection video (59 s) Image:Gray1242.png, The synovial sheaths of the tendons around the ankle. Medial aspect. (Tendon of Plantaris labeled at bottom right.) Image:Gray438-Musculus plantaris.png, Muscles of the back of the leg. Superficial layer. File:Gray440 - Plantaris.svg, Cross-section through middle of leg. Tendon of plantaris is located between soleus and gastrocnemius. File:Plantaris muscle 2.jpg, Plantaris muscle File:Space of the gastrocnemius and soleus - text.png, Plantaris tendon runs between soleus and gastrocnemius. Plantaris tendon is indicated by white arrow-heads.

References

External links

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PTCentral
{{DEFAULTSORT:Plantaris Muscle Muscles of the lower limb