Muscles Acting on the Knee

Question 1

Biceps Femoris

Answer 1

Origin: long head: ischial tuberosity; short head: lateral lip of the linea aspera
Insertion: head of fibula and lateral condyle of the tibia
Action: extends the thigh, flexes the leg
Innervation: long head: tibial nerve; short head: common fibular (peroneal) nerve
Notes: one of the “hamstring” muscles

Question 2

Gastrocnemius

Answer 2

Origin: femur; medial head: above the medial femoral condyle; lateral head: above the lateral femoral condyle
Insertion: dorsum of the calcaneus via the calcaneal (Achilles’) tendon
Action: flexes leg; plantar flexes foot
Innervation: tibial nerve
Notes: the calcaneal tendon of the gastrocnemius and soleus is the thickest and strongest tendon in the body

Question 3

Gracilis

Answer 3

Origin: pubic symphysis and the inferior pubic ramus
Insertion: medial surface of the tibia (via pes anserinus)
Action: adducts the thigh, flexes and medially rotates the thigh, flexes the leg
Innervation: anterior division of the obturator nerve
Notes: the pes anserinus is the common insertion of the gracilis, sartorius, and semitendinosus mm.(Latin, pes anserinus = goose’s foot; gracilis = slender)

Question 4

Popliteus

Answer 4

Origin: lateral condyle of the femur
Insertion: posterior surface of the tibia above soleal line
Action: flexes and rotates the leg medially (with the foot planted, it rotates the thigh laterally)
Innervation: tibial nerve
Notes: has a round tendon of origin; popliteus unlocks the knee joint to initiate flexion of the leg

Question 5

Rectus Femoris

Answer 5

Origin: straight head: anterior inferior iliac spine; reflected head: above the superior rim of the acetabulum
Insertion: patella and tibial tuberosity (via the patellar ligament)
Action: extends the leg, flexes the thigh
Innervation: femoral nerve
Notes: rectus femoris is part of the quadriceps femoris muscle

Question 6

Sartorius

Answer 6

Origin: anterior superior iliac spine
Insertion: medial surface of the tibia (pes anserinus)
Action: flexes, abducts and laterally rotates the thigh; flexes leg
Innervation: femoral nerve
Notes: its actions put the lower limb in the traditional cross-legged seated position of a tailor(Latin, sartorius = tailor)

Question 7

Semimembranosus

Answer 7

Origin: upper, outer surface of the ischial tuberosity
Insertion: medial condyle of the tibia
Action: extends the thigh, flexes the leg
Innervation: tibial nerve
Notes: one of the “hamstring” muscles

Question 8

Semitendinosus

Answer 8

Origin: lower, medial surface of ischial tuberosity (common tendon with biceps femoris m.)
Insertion: medial surface of tibia (via pes anserinus)
Action: extends the thigh, flexes the leg
Innervation: tibial nerve
Notes: pes anserinus is the common insertion for the gracilis, sartorius, and semitendinosus mm.

Question 9

Vastus Intermedius

Answer 9

Origin: anterior and lateral surface of the femur
Insertion: patella
Action: extends the leg
Innervation: femoral nerve
Notes: vastus intermedius is part of the quadriceps femoris muscle(Latin, vastus = huge)

Question 10

Vastus Lateralis

Answer 10

Origin: lateral intermuscular septum, lateral lip of the linea aspera and the gluteal tuberosity
Insertion: patella and medial patellar retinaculum
Action: extends leg
Innervation: femoral nerve
Notes: vastus lateralis is part of the quadriceps femoris muscle(Latin, vastus = huge)

Question 11

Vastus Medialis

Answer 11

Origin: medial intermuscular septum, medial lip of the linea aspera
Insertion: patella and medial patellar retinaculum
Action: extends leg
Innervation: femoral nerve
Notes: vastus medialis is part of the quadriceps femoris muscle(Latin, vastus = huge)