What is an Extensor Muscle?
Extensor muscle is defined as any of the muscles that increase the angle between the members of a limb, as by straightening either knee, elbow, or bending the spine or wrist backwards. Usually, the movement is directed backwards, with the notable knee joint exception.
Extensor Muscle in Humans
This function is named after certain muscles in the foot and hand in humans. In the human hand, these include the extensor carpi radialis longus, extensor carpi ulnaris, and extensor carpi radialis brevis that run from the humerus (upper arm bone) along the back of the forearm to the metacarpal bones at the back of the hand and that extend the wrist; the extensor digitorum that runs from the humerus to a common tendon attached to all of the fingers and that extends the extensor indicis; the fingers; that acts upon the index finger; and extensor pollicis longus, and the extensor pollicis brevis that run from the ulna (bones of the forearm) and radius, respectively, and act upon the thumb.
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Extensor Muscle in the Foot
Extensors in the foot are the extensor digitorum brevis and the extensor digitorum longus that originate at both the upper and lower parts of the lower leg and act via long tendons upon the extensor hallucis brevis, extensor hallucis longus, and the toes that act upon the great toe. Also, the foot’s long muscles aid the flexion of the ankle and the foot upward.
Extensor Digitorum Longus Muscle
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Origin and Insertion
Extensor digitorum longus muscle arises from the tibia’s lateral condyle; from the upper three-quarters of the anterior body surface of the fibula; from the deep surface of the fascia; from the upper part of the interosseous membrane; and from the intermuscular septa between it and the tibialis anterior on the peroneal and medial muscles on the lateral side. Between it and the tibialis anterior are given as the anterior tibial vessels and deep peroneal nerve’s upper portions.
This muscle passes under the inferior and superior extensor retinaculum of the foot in company with the fibularis tertius and divides into four slips that run forward on the foot’s dorsum and are inserted into the second, third phalanges of four-lesser toes.
The tendons to all the second, third, and fourth toes are each joined, opposite to the metatarsophalangeal articulations, on the lateral side of the tendon of the extensor digitorum Brevis. These tendons are inserted in the manner as explained: each receives a fibrous expansion from the lumbricals and interossei, and then spreads out into the broad aponeurosis that covers the first phalanx’s dorsal surface: at the articulation of the first with the second phalanx, this aponeurosis divides into three slips- an intermediate that is inserted into the second phalanx’s base; and two collateral slips, that after uniting on the second phalanx’s dorsal surface, are continued onward, to be inserted into the third phalanx’s base.
Extensor Hallucis Longus Muscle
Structure
The extensor hallucis longus muscle is the one that arises from the fibula’s anterior surface for up to the middle two-fourths of its extent, medial to the extensor digitorum longus muscle origin. Also, it arises from the interosseous membrane of the leg to the same extent.
Behind it and the tibialis anterior are the deep fibular nerve and the anterior tibial vessels.
Nerve Supply
The deep fibular nerve supplies the extensor hallucis longus muscle, which is a branch of the popular fibular nerve that includes the L4, L5, and S1 spinal nerve roots.
Hip Extensor Muscles
The muscles of the hip joint in human anatomy are those muscles, which cause the hip movement. Most modern anatomists describe 17 of these muscles, although a few additional muscles may be considered sometimes. The lateral rotator group, the gluteal group, the iliopsoas group, and the adductor group are commonly divided into four groups based on their orientation around the hip joint.
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Extensor Digitorum
The extensor digitorum muscle (which is also called extensor digitorum communis) is a muscle of the posterior forearm that is present in both humans and other animals. It extends the hand’s medial four digits. This extensor digitorum is innervated by the posterior interosseous nerve that is a radial nerve’s branch.
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Function of Extensor Digitorum
The extensor digitorum extends the phalanges, followed by the wrist and the elbow. The way it stretches the fingers often helps to divide them.
The extensor digitorum in the fingers acts principally on the proximal phalanges by acting to extend the metacarpophalangeal joint. The palmar and dorsal lumbrical and interossei of the hand, on the other hand, are primarily responsible for extending the distal and proximal interphalangeal joints.
Extensor Carpi Ulnaris Muscle
In the human anatomy, the extensor carpi ulnaris is defined as a skeletal muscle that is located on the ulnar side of the forearm. It acts to adduct and extend at the wrist or carpus from the anatomical position.
Extensor carpi ulnaris, being an extensor muscle, are on the posterior side of the forearm.
FAQs on Extensor Muscle
1. What are extensor muscles in the human body?
Extensor muscles are a group of muscles that cause a joint to open or straighten, increasing the angle between two bones. They work in opposition to flexor muscles. For example, when you straighten your leg, you are using your extensor muscles.
2. What is the main function of extensor muscles?
The primary function of extensor muscles is to enable extension, which is the movement of straightening a limb or a body part. They play a crucial role in everyday actions like standing up from a chair, lifting your head, straightening your fingers, and kicking a ball.
3. Can you give some examples of major extensor muscles?
Some of the most important extensor muscles in the body include:
- The quadriceps femoris in the thigh, which straightens the leg at the knee joint.
- The triceps brachii on the back of the upper arm, which straightens the arm at the elbow.
- The erector spinae group, which runs along the back and helps in straightening the spine and maintaining posture.
- The extensor digitorum in the forearm, which extends the fingers.
4. How are extensor muscles different from flexor muscles?
Extensor and flexor muscles are antagonistic pairs, meaning they have opposite functions. Extensor muscles straighten a joint (increase the angle), while flexor muscles bend a joint (decrease the angle). For instance, in your arm, the triceps is the extensor that straightens the elbow, while the biceps is the flexor that bends it.
5. How do extensor and flexor muscles work together to create smooth movement?
They work together through a process called reciprocal inhibition. When you decide to straighten a joint, your nervous system signals the extensor muscle to contract and, at the same time, sends a signal to the opposing flexor muscle to relax. This coordination prevents the muscles from working against each other, allowing for smooth, controlled, and efficient movement.
6. What causes pain in the extensor muscles of the forearm?
Pain in the forearm's extensor muscles is often caused by overuse or repetitive strain. A common example is tennis elbow (lateral epicondylitis), which is an inflammation of the tendons that connect the extensor muscles to the elbow. This can result from activities that involve repeated gripping and wrist extension, such as playing tennis, typing, or using tools.
7. Why are the extensor muscles in the back so important for daily life?
The extensor muscles of the back, particularly the erector spinae group, are vital for maintaining an upright posture. They constantly work against gravity to keep your spine straight when you are standing or sitting. Without these strong extensors, it would be difficult to stand up straight, lift objects, or even just hold your head up.
