15.19
Muscles that Move the Leg
The movement of the legs is facilitated by numerous muscles located within the anterior, medial, and posterior compartments of the thigh.
Anterior Com…
The muscles that move the legs are found in the anterior, medial, and posterior compartments of the thigh.
The quadriceps femoris is the most prominent anterior compartment muscle. It is comprised of the vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris muscles. Its primary function is knee extension.
The sartorius muscle is also present in the anterior compartment. It flexes the knee and causes lateral thigh rotation at the hip joint and is called the tailor's muscle, as it aids in cross-legged sitting.
The gracilis, a straplike muscle in the medial compartment, flexes the leg at the knee joint. Additionally, it adducts and medially rotates the thigh.
The posterior compartment muscles cause flexion at the knee and extension at the hip.
The posterior compartment includes the three hamstring muscles — the biceps femoris, the semitendinosus, and the semimembranosus. A tear of these muscles, a pulled hamstring, is a common sports injury.
The popliteus is a small muscle located posteriorly at the knee joint that aids leg movement. It causes medial rotation of the tibia to unlock an extended knee during flexion.
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Q1: What are the four muscles that make up the quadriceps femoris?
The quadriceps femoris comprises four distinct muscles: the vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris. These muscles merge to form the most prominent anterior compartment muscle of the thigh. The quadriceps tendon, shared by all four muscles, attaches to the patella and extends as the patellar ligament to the tibial tuberosity, enabling knee extension and thigh flexion.
Q2: Why is the sartorius muscle called the tailor's muscle?
The sartorius is called the tailor's muscle because it enables cross-legged sitting, a position tailors traditionally adopt while working. Located in the anterior compartment, this muscle flexes the knee and causes lateral thigh rotation at the hip joint. Its unique positioning and function make it essential for the specific posture historically associated with tailoring.
Q3: What movements does the gracilis muscle perform in the medial compartment?
The gracilis, a long, strap-like muscle in the medial compartment, performs three primary movements: it flexes the leg at the knee joint, adducts the thigh, and medially rotates the tibia during knee flexion. As the most superficial and medial of the thigh muscles, it plays a key role in coordinating leg and hip movements.
Q4: What are the three hamstring muscles and their primary function?
The three hamstring muscles are the biceps femoris, semitendinosus, and semimembranosus, located in the posterior compartment. These muscles cause flexion at the knee and extension at the hip. Hamstring tears, commonly called pulled hamstrings, are frequent sports injuries due to the significant demands placed on these muscles during leg movement.
Q5: How does the popliteus muscle unlock the knee during flexion?
The popliteus is a small, triangular muscle located at the back of the knee that initiates knee flexion and provides joint stability. It originates from the lateral femoral condyle and inserts onto the posterior tibia surface below the knee. The popliteus causes medial rotation of the tibia, a key mechanism for unlocking an extended knee and enabling smooth flexion.
Q6: What defines the popliteal fossa and which muscles form its boundaries?
The popliteal fossa is a diamond-shaped area on the back of the knee defined by specific muscle tendons. The biceps femoris muscle tendons flank it on either side, while the semitendinosus and semimembranosus tendons border it medially. This anatomical space is crucial for understanding posterior knee anatomy and the arrangement of structures supporting leg movement.
Q7: How do the adductor muscles in the medial compartment work together?
The medial compartment contains several adductor muscles including the gracilis, adductor longus, adductor brevis, and obturator externus. The adductor longus originates from the pubis and extends to the femur's linea aspera, while the adductor brevis lies deeper with a shorter, more oblique course. These muscles work together to adduct and medially rotate the thigh, coordinating complex leg movements.