An extensor muscle is any muscle that opens a joint increasing the angle between components of a limb, such as straightening the knee or elbow and bending the wrist or spine. With the exception of the knee joint the movement is directed backward. This action is known as extension.

Flexor muscles have the opposite effect, closing a joint and decreasing the angle between limb components.

In humans, some muscles include 'extensor' in their name, some include;

• Extensor carpi radialis brevis
• Extensor hallucis longus muscle
• Extensor carpi ulnaris muscle
• Extensor carpi radialis longus muscle

v • d • e Joints (TA A03.0, GA 3.284) Types fibrous: Gomphosis · Suture · Syndesmosis · Interosseous membrane cartilaginous: Synchondrosis · Symphysis synovial: Plane joint · 1° (Hinge joint, Pivot joint) · 2° (Condyloid joint, Saddle joint) · 3° (Ball and socket joint) by range of motion: Synarthrosis · Amphiarthrosis · Diarthrosis Terminology Kinesiology · Anatomical terms of motion · Agonist/Antagonist Motions general: Flexion/Extension · Adduction/Abduction · Internal rotation/External rotation · Elevation/Depression specialized/upper limbs: Protraction/Retraction · Supination/Pronation specialized/lower limbs: Plantarflexion/Dorsiflexion · Eversion/Inversion Components capsular: Articular capsule (Synovial membrane, Fibrous membrane) · Synovial fluid · Synovial bursa · Articular disk/Meniscus extracapsular: Ligament · Enthesis joint navs: anat, non-congenital arthropathies/deformities/dorsopathies/soft tissue arthropathy/congenital, eponymous signs, proc

For further reference see genetic origin.

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