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The term extrinsic in relation to muscles refers to a muscle with an origin and insertion in different body regions. For example, the biceps brachii is an extrinsic muscle as it originates in the scapula and inserts in the radius, allowing for elbow flexion. Extrinsic muscles are responsible for producing movement in multiple areas and often span multiple joints. They are distinct from intrinsic muscles, which are located entirely within the same body region. Balancing the two muscle groups is crucial for maintaining posture, preventing injury, and ensuring efficient movement.
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Examples of extrinsic muscles
The term "extrinsic muscle" refers to a muscle that originates outside of the body part it controls and crosses at least one joint. These muscles are responsible for producing movement and are attached to bones or other structures to facilitate this. They are often connected by tendons, which allow for the transfer of force and movement. Here are some examples of extrinsic muscles:
One example of an extrinsic muscle is the biceps brachii, which is located in the upper arm. This muscle originates from the scapula, or shoulder blade, and inserts on the radius bone in the forearm. It allows for elbow flexion and supination of the forearm, enabling actions such as lifting objects and turning the palm up.
Another example is the rectus femoris, one of the four muscles that make up the quadriceps in the thigh. It originates from the iliac spine of the pelvis and inserts on the patella, or kneecap, and then continues to attach to the tibia bone. This muscle is responsible for knee extension and also plays a role in hip flexion, enabling movements such as kicking and jumping.
The extrinsic muscles of the eye, or extraocular muscles, are also important to mention. These include muscles such as the lateral rectus and medial rectus, which control the horizontal movement of the eye, and the superior rectus and inferior rectus, which control vertical movement. These muscles are essential for eye movement and allow us to focus our gaze in different directions.
Additionally, we have the extrinsic muscles of the tongue, which include the genioglossus and palatoglossus muscles. The genioglossus muscle originates from the mandible, or jawbone, and inserts on the tongue, playing a crucial role in protruding and moving the tongue during speech and swallowing. The palatoglossus muscle, on the other hand, connects the palate to the tongue and aids in raising the back of the tongue and closing the soft palate during swallowing.
Lastly, let's consider the extrinsic muscles of the larynx, which include the cricothyroid muscle and the posterior cricoarytenoid muscle. The cricothyroid muscle extends from the cricoid cartilage to the thyroid cartilage and is responsible for tensing the vocal cords, thus playing a role in voice pitch modulation. The posterior cricoarytenoid muscle, on the other hand, pulls the arytenoid cartilages backward and opens the glottis during inhalation.
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Intrinsic vs. extrinsic muscles
The skeletal muscles of the hand are divided into two groups: the extrinsic and intrinsic muscles. These two groups of muscles work together to keep the body stable and aligned, contributing to both fine motor control and powerful, gross movements.
Intrinsic Muscles
Intrinsic muscles are the deep, stabilising muscles that lie close to our joints and along the spine. They are often small and less visible than extrinsic muscles, but they play a crucial role in maintaining posture and joint stability. Intrinsic muscles are responsible for fine-tuning our posture and maintaining the alignment of joints, ensuring smooth and efficient bone movement. They are designed to resist fatigue, allowing them to hold subtle contractions over long periods, which is essential for maintaining posture throughout the day.
Extrinsic Muscles
The extrinsic muscle group is called so because the muscle belly originates in the forearm. In contrast to intrinsic muscles, extrinsic muscles are larger, more superficial muscles that generate forceful movements. They are closer to the skin's surface and more prominent and visible. Extrinsic muscles are designed for short bursts of activity and can generate significant force. However, they tend to fatigue more quickly, especially when overused or relied upon for extended periods.
Examples of Intrinsic and Extrinsic Muscles
The hands, feet, tongue, and eyes all contain intrinsic and extrinsic muscles. For example, the intrinsic muscles of the hand are vital for grip and pinch strength, while the extrinsic muscles of the forearm are used to grip a baseball. In the foot, the calves are the largest muscle group acting on the ankle joint, but the underused intrinsic and extrinsic muscles of the feet need to be engaged to access the full range of motion. The extrinsic muscles of the tongue include the genioglossus, hyoglossus, styloglossus, and palatoglossus muscles, which attach the tongue to other structures. The eyes are held in place by three pairs of taut, elastic extrinsic muscles that constantly balance each other's pull.
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Functions of extrinsic muscles
Extrinsic muscles are those that lie superficially on a structure, in contrast to intrinsic muscles, which are located deeply. For example, the extrinsic muscles of the back include the trapezius, latissimus dorsi, rhomboid major and minor, levator scapulae, and serratus posterior superior and inferior muscles.
The principal function of the extrinsic muscles of the back is to move the upper extremity by controlling the movement of the scapula and humerus—important bones in the shoulder region. The interplay between the extrinsic back muscles allows for a wide range of motions, including complex actions like reaching, lifting, pulling, and pushing.
The trapezius works with other muscles to move the arm and stabilize the shoulder. The upper fibres of the trapezius elevate the scapula and rotate it during abduction of the arm. The middle fibres retract the scapula, and the lower fibres pull the scapula inferiorly. The trapezius assists the levator scapulae in lifting the scapular bone. The serratus anterior and trapezius work together to rotate the scapula superiorly, allowing the arm to reach above the head. Joint actions by the trapezius and rhomboids retract the scapula to the posterior midline, stabilizing the shoulders during motion. The trapezius helps cervical muscles move the head and neck posteriorly and laterally.
The latissimus dorsi is the largest extrinsic back muscle, spanning the entire lateral side of the back. It adducts, extends, and medially rotates the humerus. The muscle helps pull the torso superiorly and anteriorly when the arm is raised above the head. The latissimus dorsi also transversely extends and flexes the shoulder joint from an extended position.
The levator scapulae is a small strap-like muscle that begins in the neck and descends to attach to the scapula. It elevates the scapula and assists in rotating it.
The rhomboid minor muscle originates from the inferior nuchal ligament and C7-T1 spinous processes. It inserts into the medial border of the scapula superior to rhomboid major. Rhomboid major works in conjunction with other muscles to fix the scapula to the thoracic wall. It also functions to rotate and retract the scapula.
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Locations of extrinsic muscles
Extrinsic muscles are a group of muscles that lie superficially on a structure, in contrast to intrinsic muscles, which are located deeply. The extrinsic muscles in the back include the trapezius, latissimus dorsi, rhomboid major and minor, levator scapulae, and serratus posterior superior and inferior muscles. The trapezius is the most superficial of these back muscles, with fibres connecting to the shoulder and the posterior border of the distal third of the clavicle. The latissimus dorsi is the largest extrinsic back muscle, spanning the entire lateral side of the back and originating from the spinous processes of T7 to T12, thoracodorsal fascia, posterior iliac crest, and proximal third of ribs 9 through 12.
The rhomboid minor and major muscles are located superiorly, with the minor originating from the C7 and T1 vertebrae and attaching to the medial scapular border, while the major originates from T2 to T5 vertebrae and attaches just below the minor. The levator scapulae is a thin muscle that descends from the neck to the scapula, originating from the transverse processes of C1 to C4. The serratus posterior muscles are separated into superior and inferior, attaching to the ligamentum nuchae, vertebral spinous processes, and ribs.
The extrinsic muscles of the tongue include the genioglossus muscle, hyoglossus muscle, styloglossus muscle, and palatoglossus muscle. These muscles all insert into the tongue but have different origins. The genioglossus muscle originates from the mandible, while the hyoglossus muscle originates from the hyoid bone, the styloglossus muscle from the styloid process, and the palatoglossus muscle from the palatine aponeurosis.
The extrinsic extensor muscles of the hand are located in the back of the forearm and have long tendons connecting them to bones in the hand. These include muscles such as the extensor carpi radialis longus (ECRL), extensor digitorum (ED), extensor pollicis brevis (EPB), and abductor pollicis longus (APL). The ECRL has the most proximal origin of the extrinsic hand extensors, originating near the humerus. The APL originates from the lateral part of the dorsal surface of the ulna and the middle third of the dorsal surface of the radius.
The interplay between the extrinsic back muscles allows for a wide range of motions, and they are innervated by the cervical and thoracic nerves, moving the upper limb and neck.
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Impairments of extrinsic muscles
The extrinsic muscles are those that are external to a particular structure or region and are responsible for producing movement and maintaining stability in the human body. When it comes to impairments of these muscles, several factors can contribute, resulting in a range of symptoms and functional limitations.
One common impairment of the extrinsic muscles is weakness or atrophy. This can occur due to disuse or immobilization, as in the case of prolonged bed rest or when a limb is placed in a cast for an extended period. Weakness can also arise from neurological conditions such as stroke or spinal cord injuries, leading to partial or complete paralysis of the affected muscles. Additionally, muscle atrophy can result from nutritional deficiencies or underlying metabolic disorders that affect the body's ability to build and maintain muscle mass.
Another impairment of the extrinsic muscles is stiffness or a loss of flexibility. This can manifest as a reduced range of motion in the affected joints, making movements difficult and painful. Stiffness may be caused by various factors, including chronic inflammatory conditions like arthritis, or it could be the result of scar tissue formation following an injury or surgery. In some cases, stiffness can also arise from a buildup of fluid in the joints or surrounding tissues, restricting their normal range of motion.
Pain is also a common symptom associated with impairments of the extrinsic muscles. It can originate from the muscles themselves or from the associated tendons, ligaments, or joints. Muscle pain, or myalgia, can be caused by overuse or strain, leading to microscopic tears in the muscle fibers. Tendinitis, or inflammation of the tendons, can cause pain at the site of tendon attachment to the bone, and this pain is often worse with movement or activity. Ligament sprains and joint injuries can also result in pain and instability, impacting the normal functioning of the extrinsic muscles.
In more severe cases, impairments of the extrinsic muscles can lead to deformities or structural abnormalities. For example, in individuals with cerebral palsy, spasticity of the extrinsic muscles can result in fixed contractures, limiting range of motion and causing abnormal postures. Similarly, in individuals with advanced rheumatoid arthritis, the chronic inflammation and subsequent damage to the extrinsic muscles and surrounding tissues can lead to joint deformities and permanent disability.
Finally, it is important to note that impairments of the extrinsic muscles can have a significant impact on an individual's functional abilities and activities of daily living. Weakness or pain in the muscles may affect a person's ability to walk, climb stairs, or perform routine tasks that require grip strength or fine motor control. As such, comprehensive management of these impairments often involves a multidisciplinary approach, including physical therapy, occupational therapy, pain management, and in some cases, surgical intervention to restore function and improve quality of life.
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Frequently asked questions
Extrinsic muscles are muscles that have an origin and insertion in different body regions. They are responsible for producing movement in multiple areas and often span across multiple joints.
Examples of extrinsic muscles include the biceps brachii, trapezius, latissimus dorsi, rhomboid major and minor, levator scapulae, and serratus posterior superior and inferior muscles.
Intrinsic muscles have both their origin and insertion within the same region of the body. They are found entirely within the same body region, whereas extrinsic muscles have origins and insertions in different body regions.
