Dominic Stone
Extensor muscles are responsible for increasing the angle between bones or body surfaces at a joint, resulting in straightening or extension. This is in contrast to flexor muscles, which decrease the angle between bones, resulting in bending. Extensor muscles are found in various parts of the body, including the hand, wrist, elbow, spine, knee, and foot, and they work in conjunction with flexor muscles to allow for a wide range of movements. For example, in the hand, extensor muscles such as the extensor digitorum extend the fingers, while in the wrist, muscles like the extensor carpi radialis brevis, extensor carpi radialis longus, and extensor carpi ulnaris act together to produce wrist extension. Understanding the function and anatomy of extensor muscles is crucial for treating injuries and maintaining overall body movement and flexibility.
| Characteristics | Values |
|---|---|
| Definition | Extensor muscles increase the angle between members of a limb, resulting in straightening of the bones or body surfaces involved. |
| Direction of movement | Usually backward, except in the case of the knee joint. |
| Extensor muscles in the hand | Extensor carpi radialis brevis, extensor carpi radialis longus, and extensor carpi ulnaris, extensor digitorum, extensor indicis, extensor pollicis brevis, and extensor pollicis longus. |
| Extensor muscles in the foot | Extensor digitorum longus and extensor digitorum brevis. |
| Extensor muscles in the forearm | Brachioradialis, extensor carpi radialis muscles, extensor digitorum, extensor digiti minimi, and anconeus. |
| Extensor muscles in the wrist | Extensor carpi radialis brevis, extensor carpi radialis longus, and extensor carpi ulnaris act synergistically to achieve neutral wrist extension movements. |
| Extensor muscles in the thumb | Abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus. |
| Extensor muscles in the fingers | Extensor digitorum communis muscles. |
| Innervation | Extensor muscles are innervated by the radial nerve. |
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What You'll Learn
Extensor muscles increase the angle between bones in a limb
Extensor muscles are those that increase the angle between bones in a limb, resulting in straightening. They are the opposite of flexor muscles, which decrease the angle between bones and cause bending. For example, flexor muscles are responsible for bending the elbow and knee, while extensor muscles are responsible for straightening the elbow and knee.
In the hand, extensor muscles include the extensor carpi radialis brevis, extensor carpi radialis longus, and extensor carpi ulnaris, which run from the upper arm bone (humerus) along the back of the forearm to the metacarpal bones at the back of the hand, extending the wrist. The extensor digitorum runs from the humerus to a common tendon attached to all the fingers and extends them. The extensor indicis acts upon the index finger, while the extensor pollicis brevis and extensor pollicis longus act upon the thumb.
Extensors in the foot include the extensor digitorum longus and extensor digitorum brevis, which originate in the lower leg and act on the toes through long tendons. The extensor digitorum longus and extensor digitorum brevis are two extensors that originate in the lower leg and act on the toes through long tendons.
The muscles in the posterior compartment of the forearm are commonly referred to as extensor muscles. They are organised into two layers: deep and superficial. These layers are separated by a layer of fascia. The extensor carpi radialis muscles are situated on the lateral aspect of the posterior forearm, allowing them to produce both abduction and extension at the wrist. The brachioradialis muscle is a paradoxical muscle; its origin and innervation are characteristic of an extensor muscle, but it is a flexor at the elbow. The anconeus is situated proximally in the extensor compartment of the forearm and contributes to extending and stabilising the elbow joint.
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They are involved in straightening the elbow or knee
Extensor muscles are involved in straightening the elbow or knee. They increase the angle between the bones of a limb, which results in straightening. For example, extension is produced by extending the flexed (bent) elbow. Straightening of the arm requires extension at the elbow joint.
Extensors in the hand include the extensor carpi radialis brevis, extensor carpi radialis longus, and extensor carpi ulnaris, which run from the humerus (upper arm bone) along the back of the forearm to the metacarpal bones at the back of the hand, extending the wrist. The extensor digitorum extends the fingers, the extensor indicis acts upon the index finger, and the extensor pollicis brevis and extensor pollicis longus act upon the thumb.
The extensor digitorum is the main extensor of the fingers. To test its function, the forearm is pronated, and the fingers are extended against resistance. It originates from the lateral epicondyle, and its tendon continues into the distal part of the forearm, where it splits into four and inserts into the extensor hood of each finger.
The anconeus is an extensor muscle situated proximally in the extensor compartment of the forearm. It extends and stabilizes the elbow joint. It originates from the lateral epicondyle and attaches to the posterior and lateral part of the olecranon.
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Extensor muscles are also used to bend the wrist or spine backward
Extensor muscles are those that increase the angle between bones of a limb, resulting in straightening. They are the opposite of flexor muscles, which decrease the angle between bones and cause bending. Extensor muscles are found in the hand, foot, arm, and leg.
In the hand, extensor muscles include the extensor carpi radialis brevis, extensor carpi radialis longus, and extensor carpi ulnaris. These muscles run from the upper arm bone (humerus) along the back of the forearm to the metacarpal bones at the back of the hand, and they extend the wrist. The extensor digitorum, which runs from the humerus to a common tendon attached to all fingers, extends the fingers. The extensor indicis acts upon the index finger, while the extensor pollicis brevis and extensor pollicis longus act upon the thumb.
Extensors in the foot include the extensor digitorum longus and extensor digitorum brevis, which originate in the lower leg and act on the toes. The extensor digitorum longus and extensor digitorum brevis muscles are responsible for extending the toes.
The extensor muscles in the posterior compartment of the forearm are commonly known as the extensor muscles. These muscles produce extension at the wrist and fingers. They are innervated by the radial nerve and are organised into two layers: deep and superficial.
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They are innervated by the radial nerve
Extensor muscles are involved in the movement of joints that increase the angle between two bones or body surfaces at a joint, resulting in straightening. For example, extension is produced by extending the flexed (bent) elbow. Straightening of the arm requires extension at the elbow joint.
The radial nerve is a peripheral nerve supplying specific parts of the arm, forearm, wrist, and hand. It has both motor and sensory functions. The motor branches stimulate the posterior arm muscles, posterior forearm muscles, and extrinsic wrist and hand extensors. The radial nerve originates from the ventral rami of the spinal nerves C5 to T1 and is part of the posterior cord of the brachial plexus.
The radial nerve descends between the deep and superficial extensor muscles and lies on the interosseous membrane. It ends in a flattened expansion. The nerve passes through the axilla, where it lies behind the axillary and upper brachial arteries, and continues anterior to the tendons of the teres minor, latissimus dorsi, and subscapularis.
The radial nerve is responsible for innervating the muscles located in the posterior arm and posterior forearm. It innervates the three heads of the triceps brachii, allowing for extension of the arm at the elbow. The nerve also gives rise to branches that supply the brachioradialis and extensor carpi radialis longus, which are muscles of the posterior forearm.
Damage to the radial nerve can result in wrist drop, a condition characterized by the inability to extend the wrist. This can occur due to a lateral supracondylar fracture or a midhumeral injury. Iatrogenic radial nerve damage can also lead to neurologic deficits distal to the injury site.
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Extensors in the foot include the extensor digitorum longus and brevis
Extensor muscles help in straightening or extending the angle between bones or body surfaces at a joint, while flexor muscles help in bending body parts like the elbow, knee, and fingers. In the hand, extensor muscles include the extensor carpi radialis brevis, extensor carpi radialis longus, and extensor carpi ulnaris, which extend the wrist.
The extensor digitorum brevis arises from the proximal lateral calcaneus, the interosseous talocalcaneal ligament, and the inferior extensor retinaculum. It passes medially over the foot and inserts on the lateral sides of the tendons of the extensor digitorum longus muscle of the second, third, and fourth toes. The extensor digitorum brevis extends the second, third, and fourth toes, counteracting the obliquity given to the toes by the long extensor to produce an even extension when both muscles contract.
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Frequently asked questions
Extensor muscles are muscles that increase the angle between members of a limb, resulting in straightening.
Extensor muscles help in straightening or extending the elbow or knee or bending the wrist or spine backward.
Extensor muscles are located in the posterior forearm, hand, and foot.
Some examples of extensor muscles include the extensor carpi radialis brevis, extensor carpi radialis longus, and extensor digitorum.
