Illustration of the normal human anatomy of a knee, front view. Shown are the femur (top), patella (heart-shaped, center), lateral and medial femoral condyles (purple left and right, respectively), fibula (bottom left), and tibia (bottom right).

Illustration of a the normal human anatomy of the tibial plateau (top view). Shown also are the posterior cruciate ligament, medial meniscus, anterior cruciate ligament, and transverse ligament.

Illustration of the normal human anatomy of a knee, anterolateral view. Shown are the patella, anterior cruciate ligament, patellar ligament, fibular collateral ligament, lateral meniscus, lateral femoral condyle, femur, tibia, and fibula.

Illustration of the normal human anatomy of a knee, dorsal view. Shown are the femur, posterior cruciate ligament, anterior cruciate ligament, articular surfaces of the lateral and medial condyles of the femur, lateral meniscus, fibular collateral ligament, fibula, tibia, medial meniscus, and tibial collateral ligament.

Illustration of ligament tears in a human knee, showing a posterior cruciate ligament tear, medial meniscus ligament tear, tibial collateral ligament tear, partial fibular ligament tear, and anterior cruciate ligament rupture.

Illustration of the normal human anatomy of a knee, dorsal medial view. Shown are the medial femoral condyle, medial meniscus, tibial collateral ligament, femur, fibula, and tibia.

Capillary cell wall.

Illustration of fibromyalgia pain points. The muscular system of a female figure (anterior and posterior views) shows the location of tender spots (pain points) on the body that are caused by fibromyalgia. Fibromyalgia has been associated with peripheral and central sensitization.

Illustration of a normal human heart, cutaway anterior view. Shown are the left and right atria, left and right ventricles, pulmonary artery valve, and ascending aorta lumen. Major arteries and veins associated with the heart are also shown.

Anatomical structure of the penis shaft: corpora cavernosa, corpus spongiosum, urethra, central arteries, connective tissue layers (tunica), dorsal veins and arteries, subcutaneous tissue, and skin. A detail of the corpus cavernosum shows the cavernous sinuses that fill with blood to produce an erection, and the supplying artery and draining vein.

Dopamine mediated neurotransmission. Dopamine is involved with brain processes that control movement, emotional response, and the ability to experience pleasure and pain.

Illustration of a cross section of a normal eye.

Illustration of a cross section of a normal eye.

Illustration of the external testicular anatomy showing the epididymis, appendix testis, tunica vaginalis, and the spermatic and cremasteric fascia.

Illustration of a normal human brain, lateral external view.

Illustration of the normal eye anatomy, midsagittal section.

Illustration of the arterial tree in the human body.

Illustration of the arteries of the normal human brain.

Illustration of the base of the brain, shown without the cerebellum and brain stem, viewed from below.

Illustration of the normal human brain, sagittal section.