The plantaris is one of the superficial
muscle
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
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, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its ability ...
. 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 calcaneus (h ...
, the plantaris tendon (which tends to be between in length) is the longest tendon in the
human body
The human body is the 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 systems. They ensure homeostasis and the life, viabi ...
. 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
The gastrocnemius muscle (plural ''gastrocnemii'') is a superficial two-headed muscle that is in the back part of the lower leg of humans. It runs from its two heads just above the knee to the heel, a three joint muscle (knee, ankle and subtalar ...
and
soleus
In humans and some other mammals, the soleus is a powerful muscle in the back part of the lower leg (the calf). It runs from just below the knee to the heel, and is involved in standing and walking. It is closely connected to the gastrocnemius mu ...
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
Early modern human (EMH) or anatomically modern human (AMH) are terms used to distinguish ''Homo sapiens'' (the only extant Hominina species) that are anatomically consistent with the range of phenotypes seen in contemporary humans from extin ...
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 (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
at a position slightly superior to the origin of the lateral head of
gastrocnemius
The gastrocnemius muscle (plural ''gastrocnemii'') is a superficial two-headed muscle that is in the back part of the lower leg of humans. It runs from its two heads just above the knee to the heel, a three joint muscle (knee, ankle and subtalar ...
. 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 hu ...
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 calcaneus (h ...
. It occasionally separately inserts into the medial side of the
calcaneus
In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock.
S ...
.
Innervation
The plantaris muscle is innervated by the
tibial nerve
The tibial nerve is a branch of the sciatic nerve. The tibial nerve passes through the popliteal fossa to pass below the arch of soleus.
Structure Popliteal fossa
The tibial nerve is the larger terminal branch of the sciatic nerve with root val ...
, a branch of the
sciatic nerve in the
sacral plexus
In human anatomy, the sacral plexus is a nerve plexus which provides motor and sensory nerves for the posterior thigh, most of the lower leg and foot, and part of the pelvis. It is part of the lumbosacral plexus and emerges from the lumbar verte ...
. 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 groove betwe ...
of the
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
with the
pre-central gyrus
The precentral gyrus is a prominent gyrus on the surface of the posterior frontal lobe of the brain. It is the site of the primary motor cortex that in humans is cytoarchitecture, cytoarchitecturally defined as Brodmann area 4.
Structure
The pr ...
(
primary motor cortex).
Upper motor neuron
Upper motor neurons (UMNs) is a term introduced by William Gowers in 1886. They are found in the cerebral cortex and brainstem and carry information down to activate interneurons and lower motor neurons, which in turn directly signal muscles t ...
s are stimulated and send a signal through the
internal capsule
The internal capsule is a white matter structure situated in the inferomedial part of each cerebral hemisphere of the brain. It carries information past the basal ganglia, separating the caudate nucleus and the thalamus from the putamen and the ...
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 neur ...
. Decussation of the
lateral corticospinal tract
The lateral corticospinal tract (also called the crossed pyramidal tract or lateral cerebrospinal fasciculus) is the largest part of the corticospinal tract. It extends throughout the entire length of the spinal cord, and on transverse section appe ...
occurs in the
medullary pyramids
In neuroanatomy, the medullary pyramids are paired white matter structures of the brainstem's medulla oblongata that contain motor fibers of the corticospinal and corticobulbar tracts – known together as the pyramidal tracts. The lower limit ...
, 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, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...
. Upper motor neurons synapse with
lower motor neuron
Lower motor neurons (LMNs) are motor neurons located in either the anterior grey column, anterior nerve roots (spinal lower motor neurons) or the cranial nerve nuclei of the brainstem and cranial nerves with motor function (cranial nerve lower mo ...
s 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 nerve
The common fibular nerve (also known as the common peroneal nerve, external popliteal nerve, or lateral popliteal nerve) is a nerve in the lower leg that provides sensation over the posterolateral part of the leg and the knee joint. It divides at ...
s. The tibial nerve runs medially at 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 hu ...
. 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
The oblique popliteal ligament (posterior ligament) is a broad, flat, fibrous band on the posterior knee representing an expansion of the tendon of the semimembranosus muscle. It attaches onto the intercondylar fossa and lateral condyle of the f ...
. Interdigitations with the lateral head of the
gastrocnemius
The gastrocnemius muscle (plural ''gastrocnemii'') is a superficial two-headed muscle that is in the back part of the lower leg of humans. It runs from its two heads just above the knee to the heel, a three joint muscle (knee, ankle and subtalar ...
and a fibrous extension of the muscle to the
patella
The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as m ...
are not unusual.
Function
The plantaris acts to weakly
plantar flex the
ankle joint
The ankle, or the talocrural region, or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular join ...
and flex 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 hu ...
.
The plantaris muscle may also provide
proprioceptive
Proprioception ( ), also referred to as kinaesthesia (or kinesthesia), is the sense of self-movement, force, and body position. It is sometimes described as the "sixth sense".
Proprioception is mediated by proprioceptors, mechanosensory neurons ...
feedback information to the
central nervous system
The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
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 are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including huma ...
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
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscle ...
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.
See also
*
Compartmental syndrome
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
In humans and some other mammals, the soleus is a powerful muscle in the back part of the lower leg (the calf). It runs from just below the knee to the heel, and is involved in standing and walking. It is closely connected to the gastrocnemius mu ...
and gastrocnemius
The gastrocnemius muscle (plural ''gastrocnemii'') is a superficial two-headed muscle that is in the back part of the lower leg of humans. It runs from its two heads just above the knee to the heel, a three joint muscle (knee, ankle and subtalar ...
.
File:Plantaris muscle 2.jpg, Plantaris muscle
File:Space of the gastrocnemius and soleus - text.png, Plantaris tendon runs between soleus
In humans and some other mammals, the soleus is a powerful muscle in the back part of the lower leg (the calf). It runs from just below the knee to the heel, and is involved in standing and walking. It is closely connected to the gastrocnemius mu ...
and gastrocnemius
The gastrocnemius muscle (plural ''gastrocnemii'') is a superficial two-headed muscle that is in the back part of the lower leg of humans. It runs from its two heads just above the knee to the heel, a three joint muscle (knee, ankle and subtalar ...
. Plantaris tendon is indicated by white arrow-heads.
References
External links
*
PTCentral
{{DEFAULTSORT:Plantaris Muscle
Muscles of the lower limb