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The human body is a fascinating machine, with muscles that allow us to move, breathe, and even defecate. One type of muscle, known as a bipennate muscle, is characterised by its feather-like structure. Bipennate muscles, such as the biceps, have muscle fibres that attach at an angle to a central tendon, resembling two rows of feathers facing in opposite diagonal directions. This unique structure allows for greater force production, although it results in a smaller range of motion. The biceps tendon, for example, has a short and long head, with distinct insertions onto the radius. The arrangement of muscle fibres in bipennate muscles enables the packing of more sarcomeres in parallel, contributing to their force-generating capacity.
| Characteristics | Values |
|---|---|
| Definition | A type of skeletal muscle with fascicles that attach obliquely (in a slanting position) to its tendon |
| Etymology | The term "pennate" comes from the Latin "pinnatus" ("feathered, winged"), from Latin "pinna" ("feather, wing") |
| Types | Unipennate, Bipennate, Multipennate |
| Unipennate Definition | A pennate muscle where all the fascicles are on the same side of the tendon |
| Bipennate Definition | A pennate muscle where there are fascicles on both sides of the central tendon |
| Multipennate Definition | A pennate muscle where the central tendon branches within the muscle |
| Examples of Bipennate Muscles | Rectus femoris, Gastrocnemius, Biceps |
| Examples of Unipennate Muscles | Flexor pollicis longus, Lumbricals, Extensor digitorum communis (wrist and finger extensor) |
| Examples of Multipennate Muscles | Deltoid muscle, Psoas major |
| Characteristics | Higher force production but a smaller range of motion; more muscle fibres; shorter fibres; slower contraction |
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What You'll Learn
Bipennate muscles have two rows of muscle fibres
Bipennate muscles are a type of skeletal muscle. They are characterised by having two rows of muscle fibres, which are obliquely set on both sides of a central tendon. This is in contrast to unipennate muscles, which have fascicles on only one side of the tendon, and multipennate muscles, which have multiple rows of diagonal fibres. The name 'bipennate' comes from the Latin word 'pinnatus', meaning 'feathered' or 'winged'. This name reflects the feather-like appearance of the muscle, with fibres on both sides of the tendon resembling a feather's structure.
The biceps tendon is an example of a bipennate muscle, with a short and a long head. The long head originates from the supraglenoid tubercle, while the short head originates from the coracoid process. Another example of a bipennate muscle is the rectus femoris, a large muscle in the quadriceps responsible for thigh flexion.
The structure of bipennate muscles allows for greater force production compared to other muscle types. This is because the arrangement of fibres in bipennate muscles enables more sarcomeres to be packed in parallel, increasing the force-producing capacity of the muscle. However, the larger the pennation angle, or angle between the muscle fibres and the direction of action, the smaller the force in that direction. Bipennate muscles also have a smaller range of motion compared to other muscle types.
The shape and structure of skeletal muscles, including bipennate muscles, can be classified in several ways. One way is by the arrangement of their fascicles, or bundles of muscle fibres. Parallel muscles, for example, have fascicles that are arranged in the same direction as the long axis of the muscle. Another way to classify skeletal muscles is by their shape. For instance, fusiform muscles are more spindle-shaped, while non-fusiform muscles have a constant diameter.
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They have fibres that face in opposite diagonal directions
A bipennate muscle is a type of skeletal muscle. Skeletal muscles are voluntary muscles that surround and support our skeleton and move our bones. They are enclosed in connective tissue scaffolding at three levels. Each muscle fibre (cell) is covered by endomysium and the entire muscle is covered by epimysium. When a group of muscle fibres is "bundled" as a unit within the whole muscle, it is called a fascicle.
A bipennate muscle has two rows of muscle fibres, with fibres that face in opposite diagonal directions, and a central tendon. The name "pennate" comes from the Latin "pinnatus", meaning "feathered" or "winged". The tendon runs through the length of the muscle, with the fascicles attaching at an angle. This is similar to the quill of a feather, with the muscle fascicles forming angles that give them a feather-like appearance.
The rectus femoris, a large muscle in the quadriceps, is an example of a bipennate muscle. The deltoid muscle of the shoulder is an example of a multipennate muscle, which has multiple rows of diagonal fibres, with a central tendon that branches into two or more tendons.
Bipennate muscles have a large number of muscle fibres per unit and so are very strong, but they tire easily. By packing more sarcomeres in a muscle, more force can be developed. However, as the angle of pennation increases, an increasing portion of the force developed by sarcomeres is displaced away from the tendons.
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They have a central tendon, like a feather
The term "bipennate" comes from the Latin "pennatus", meaning "feathered" or "winged". Pennate muscles, or penniform muscles, are so-called because they resemble feathers, with the muscle fascicles attaching at an angle to a central tendon that runs through the muscle's length. Bipennate muscles, in particular, have two rows of muscle fibres, or fascicles, that are obliquely set on both sides of a central tendon, like the barbs of a feather.
The biceps tendon is a well-known example of a bipennate muscle, with a short and a long head. The long head originates from the supraglenoid tubercle and the short head from the coracoid process. The rectus femoris, a large muscle in the quadriceps, is another example of a bipennate muscle.
The structure of bipennate muscles allows for a greater number of muscle fibres to be packed in parallel, increasing the force of the muscle. However, this comes at the cost of a smaller range of motion. The speed of contraction is also affected, with larger pennation angles resulting in slower contractions.
The bipennate structure is just one of several types of muscle structures, including unipennate, multipennate, fusiform, and convergent. Unipennate muscles have fascicles on only one side of the tendon, while multipennate muscles have multiple rows of diagonal fibres that branch into two or more tendons. Fusiform muscles are spindle-shaped, with a larger central region or "muscle belly" tapering to tendons at each end. Convergent muscles have a common point of attachment, with fascicles extending outward, allowing them to cover a broad surface.
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They allow the muscle to produce more force
The structure of a bipennate muscle allows it to produce more force than other muscle types. A bipennate muscle has two rows of muscle fibres, with the fibres on either side of a central tendon, resembling the structure of a feather. This is in contrast to unipennate muscles, where the fascicles are located on one side of the tendon, and multipennate muscles, where the fascicles converge on multiple tendons that taper towards a common tendon.
The structure of bipennate muscles allows for a greater number of muscle fibres to be packed in parallel, which results in increased force production. This is because the fascicles, or bundles of muscle fibres, attach obliquely to the tendon at an angle, known as the pennation angle. The larger the pennation angle, the more sarcomeres can be packed in parallel, increasing the force-producing capacity of the muscle.
However, it is important to note that as the pennation angle increases, a larger portion of the force developed by the sarcomeres is displaced away from the tendon. Therefore, the maximum force in the direction of action is slightly lower than the maximum force in the fibre direction. Additionally, the larger the pennation angle, the shorter the muscle fibres, which results in slower contraction speeds.
Examples of bipennate muscles include the biceps, rectus femoris, and gastrocnemius. The biceps tendon, for instance, is composed of a short and a long head, with distinct insertions onto the radius. The short head acts as a more powerful elbow flexor, while the long head acts as a more powerful supinator.
In summary, the structure of bipennate muscles, with their two rows of muscle fibres and central tendon, allows for increased force production due to the packing of more sarcomeres in parallel. However, this comes at the cost of a reduced range of motion and slower contraction speeds.
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They are a type of skeletal muscle
A bipennate muscle is a type of skeletal muscle. Skeletal muscles are voluntary muscles that surround and support our skeleton and move our bones. They are enclosed in connective tissue scaffolding at three levels. Each muscle fibre (cell) is covered by endomysium, and the entire muscle is covered by epimysium. When a group of muscle fibres is "bundled" as a unit within the whole muscle, it is called a fascicle. Fascicles are covered by a layer of connective tissue called perimysium.
Bipennate muscles are a type of pennate muscle, which is also called a penniform muscle. The term pennate comes from the Latin "pinnatus", meaning feathered or winged. Pennate muscles have a large number of muscle fibres and are very strong, but they tire easily. In a bipennate muscle, the fascicles are located on both sides of the tendon, like the arrangement of a single feather. The rectus femoris, a large muscle in the quadriceps, is an example of a bipennate muscle. The biceps tendon is also a bipennate muscle, comprising a short and a long head.
The other types of pennate muscles are unipennate and multipennate. In a unipennate muscle, the fascicles are located on one side of the tendon. In a multipennate muscle, the central tendon branches within the muscle, and the fascicles insert on multiple tendons, tapering towards a common tendon.
The advantage of pennate muscles is that they can pack more muscle fibres in parallel, allowing them to produce more force. However, the fibre angle to the direction of action means that the maximum force in that direction is less than the maximum force in the fibre direction. As the pennation angle increases, an increasing portion of the force developed by the muscle fibres is displaced away from the tendons.
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Frequently asked questions
A bipennate muscle is a type of skeletal muscle with fascicles that attach obliquely to a tendon on both sides. This structure allows for greater force production but a smaller range of motion.
Examples of bipennate muscles include the rectus femoris, gastrocnemius, and biceps tendon.
In a unipennate muscle, the fascicles are located on only one side of the tendon. Unipennate muscles include certain muscles in the hand, such as the flexor pollicis longus and the extensor digitorum of the forearm.
Multipennate muscles have multiple rows of diagonal fibres, with a central tendon that branches into two or more tendons. Examples of multipennate muscles include the deltoid muscle and the psoas major.
