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Multipennate muscles are a type of muscle with a unique structure and function. They are characterised by diagonal muscle fibres that converge into multiple tendons, resembling a feathered or winged shape. This architectural arrangement allows for greater force production and has interesting implications for muscle function and movement. The term multipennate itself refers to the Latin pinnatus, meaning feathered or winged. This anatomical structure is observed in specific muscles, such as the deltoid muscle in the human shoulder. Understanding the architecture of multipennate muscles provides insight into the diverse ways muscles adapt and function to support the body.
| Characteristics | Values |
|---|---|
| Definition | Muscles in which the fibers are arranged in curved bundles in one or more planes |
| Example | Sphincters |
| Shape | Resembles the shape of a feather |
| Muscle Fibers | Shorter than they would be if they ran from one end of the muscle to the other |
| Force | Higher force production but a smaller range of motion |
| Pennation Angle | Increases when the muscle contracts and shortens |
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What You'll Learn
Multipennate muscles are a type of pennate muscle
The force produced by a given muscle is proportional to the cross-sectional area, or the number of parallel sarcomeres present. The cross-sectional area of a muscle is also known as the anatomical cross-sectional area (ACSA). In pennate muscles, the muscle fibres are shorter than they would be if they ran from one end of the muscle to the other, and the larger the pennation angle, the shorter the fibres. This allows for a greater number of fibres to be present in the muscle, increasing the cross-sectional area. As a result, the cross-sectional area of a pennate muscle does not accurately represent the number of muscle fibres in the muscle.
The total force exerted by the fibres along their oblique direction is proportional to the physiological cross-sectional area (PCSA). In a pennate muscle, the PCSA is always larger than the ACSA. The maximum force of a muscle fibre depends on its thickness (cross-sectional area) and type, and not on its mass or length alone. The speed at which a muscle fibre can shorten is partly determined by the length of the muscle fibre.
Multipennate muscles, such as the deltoid muscle in the human shoulder, have fibres that are oriented at multiple angles along the force-generating axis. As pennation increases (from unipennate to bipennate to multipennate), the muscle fibres become shorter, the number of fibres increases, and the cross-sectional area of the fibres increases. This results in a greater force-producing capacity in multipennate muscles compared to unipennate or bipennate muscles.
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They have diagonal muscle fibres in multiple rows
Multipennate muscles, also known as pennate or pinnate muscles, are a type of skeletal muscle with fibres that attach obliquely, or diagonally, to its tendon. The name "pennate" comes from the Latin "pinnatus", meaning feathered or winged. This is because the muscle fibres of a multipennate muscle approach a central tendon at an angle, resembling the shape of a feather.
The fibres of a multipennate muscle are shorter than they would be if they ran from one end of the muscle to the other. This is because the tendon in a multipennate muscle extends for some distance along the length of the belly, or main body, of the muscle. The fibres of a multipennate muscle are also packed in parallel, allowing the muscle to produce more force.
The fibres of a multipennate muscle are arranged in curved bundles in one or more planes. This means that the muscle fibres are not parallel to one another, but instead form an angle to the load axis of the muscle. This angle is known as the pennation angle. When a multipennate muscle contracts and shortens, the pennation angle increases.
The muscle cross-sectional area (ACSA) does not accurately represent the number of muscle fibres in a multipennate muscle. This is because the ACSA is calculated based on the length of the muscle, rather than the number of fibres. A better estimate of the number of muscle fibres is provided by the total area of the cross-sections perpendicular to the muscle fibres, known as the physiological cross-sectional area (PCSA).
The PCSA of a multipennate muscle is always larger than the ACSA. This is because the fibres of a multipennate muscle are shorter and more numerous than those of a non-pennate muscle. The maximum force of a multipennate muscle fibre depends on its thickness, or cross-sectional area, and type, rather than its mass or length alone.
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The central tendon branches into two or more tendons
Pennate muscles are named after their resemblance to the shape of a feather, with muscle fibres approaching a central tendon at an oblique angle. This structure maximises the muscle's force potential, making it well-suited for generating large forces to support or propel the body weight.
The central tendon of a multipennate muscle branches into two or more tendons. Multipennate muscles have multiple rows of muscle fibres, with the central tendon branching within the muscle. This is in contrast to unipennate muscles, where the tendon extends along one side of the belly, and bipennate muscles, where the tendon courses through the centre of the belly.
The deltoid muscle, which lies over the shoulder joint, is an example of a multipennate muscle. It can be broken down into the anterior deltoid, lateral deltoid, and posterior deltoid. The rectus femoris, found in the thigh, is an example of a bipennate muscle, with fascicles on both sides of the tendon.
The differing ways in which fascicles attach to tendons create a variety of skeletal muscle sizes and shapes. As the number of tendons increases, the muscle fibres become shorter, the number of fibres increases, and the cross-sectional area of the fibres increases. The muscle fibres in a pennate muscle can only pull at an angle, and as a result, contracting pennate muscles do not move their tendons very far. However, because a pennate muscle generally can hold more muscle fibres within it, it can produce relatively more tension for its size, compared to non-pennate muscles.
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Multipennate muscles include the human shoulder's deltoid muscle
Multipennate muscles are a type of skeletal muscle with a feather-like shape. They are characterised by fascicles that attach obliquely (in a slanting position) to their tendon. This structure allows for a greater number of muscle fibres, resulting in increased force production but a smaller range of motion. The degree of fibre angle change in multipennate muscles varies under different loading conditions.
The deltoid muscle, forming the rounded contour of the human shoulder, is an example of a multipennate muscle. It is also known as the 'common shoulder muscle' and is made up of three distinct sets of muscle fibres: the anterior or clavicular part, the posterior or scapular part, and the intermediate or acromial part. These three parts of the deltoid contract simultaneously to assist in abducting the arm past 15 degrees. The deltoid muscle is a key shoulder stabiliser, preventing inferior glenohumeral joint displacement during heavy lifting. It also compensates for weak shoulder abduction due to rotator cuff tears.
The deltoid muscle is superficial, meaning it is close to the surface of the skin, and it covers the front, side, and back of the shoulder joint. It is responsible for flexion (moving the arm forward) and extension (moving the arm backward), as well as arm abduction, which is raising the arm out to the side of the body. The deltoid muscle also works in tandem with other shoulder muscles, such as the rotator cuff muscles, to enable a variety of movements.
The deltoid muscle receives blood from the thoracoacromial branch of the axillary artery, with minor contributions from other arteries. It is vulnerable to conditions such as adhesive capsulitis, axillary nerve palsy, bursitis, and deltoid fibrosis, which can cause pain, stiffness, and loss of muscle strength and mobility.
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They are characterised by curved fibre bundles in one or more planes
Multipennate muscles are a type of skeletal muscle with a unique structure. They are characterised by their fibres, which are arranged in curved bundles in one or more planes. This is in contrast to other types of muscles, such as fusiform muscles, which have fibres that run parallel to one another, forming a spindle shape.
The name "multipennate" comes from the Latin "pinnātus", meaning ""feathered" or "winged". This name is fitting, as multipennate muscles resemble the shape of a feather. They have muscle fibres that approach a central tendon at an oblique angle, similar to the arrangement of feathers on a wing.
The curved fibre bundles of multipennate muscles can be observed in the sphincters, for example. This structure allows for a greater number of muscle fibres to be packed in parallel, resulting in the ability to produce more force. However, the oblique angle of the fibres also means that the maximum force in the direction of action is somewhat less than the maximum force in the fibre direction.
The specific tension of the muscle fibres in a multipennate muscle can be calculated if the muscle's PCSA (physiological cross-sectional area) is known. The PCSA is a better estimate of the number of muscle fibres than the ACSA (anatomical cross-sectional area), as the latter does not accurately represent the number of muscle fibres in this type of muscle.
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Frequently asked questions
Muhl-tih-PEH-nate.
Multipennate muscles are a type of pennate or pinnate muscle. Pennate muscles are a type of skeletal muscle with fascicles that attach obliquely (in a slanting position) to its tendon. Multipennate muscles have diagonal muscle fibres in multiple rows with the central tendon branching into two or more tendons.
Examples of multipennate muscles include the deltoid muscle in the shoulder of humans and the sphincters.
Multipennate muscles can produce more force than other muscle types as they can pack in more muscle fibres in parallel. However, the maximum force in the direction of the muscle is less than the maximum force in the fibre direction.
