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A unipennate muscle is a type of skeletal muscle with fibres that attach to one side of a tendon in an oblique or slanting position. This structure allows for greater strength, but a smaller range of motion. Examples of unipennate muscles include the extensor digitorum longus in the lower leg, the lumbricals in the hand, and the extensor digitorum communis in the wrist and fingers.
| Characteristics | Values |
|---|---|
| Definition | If all the fascicles are on the same side of the tendon, the pennate muscle is called unipennate. |
| Muscle type | Skeletal |
| Muscle fibres | Arranged to insert in a diagonal direction onto the tendon, allowing great strength. |
| Examples | Extensor digitorum longus (found in the lateral, lower leg), Lumbricals (deep hand muscles), Extensor Digitorum Communis (wrist and finger extensor) |
| Comparison to other muscles | Unipennate muscles have shorter fibres than bipennate muscles. |
| Comparison to other pennate muscles | As pennation increases (unipennate to multipennate), the muscle fibres become shorter, the number of fibres increases, and the cross-sectional area of the fibres increases. |
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What You'll Learn
- Unipennate muscles have fibres that attach to one side of the tendon
- Examples of unipennate muscles include the extensor digitorum longus and the extensor digitorum communis
- Unipennate muscles are stronger than bipennate or multipennate muscles
- Unipennate muscles are found in the hand and wrist
- Unipennate muscles have a larger number of muscle fibres per unit
Unipennate muscles have fibres that attach to one side of the tendon
The structure of a muscle is defined by the way its fascicles attach to tendons. Fascicles are bundles of muscle fibres enclosed in connective tissue. The arrangement of these fascicles determines the shape and function of the muscle.
Pennate muscles are a type of skeletal muscle with fascicles that attach obliquely (in a slanting position) to the tendon. This type of muscle generally allows higher force production but a smaller range of motion. The term "pennate" comes from the Latin "pinnātus" ("feathered, winged"), from "pinna" ("feather, wing"). The fascicles in a pennate muscle are attached like the plumes of a feather to an elongate tendon. This is typical of muscles of the limbs.
The structure of a unipennate muscle can be compared to a feather attached to a central shaft at one end. The fascicles are located on one side of the tendon, forming an angle (the pennation angle) to the load axis of the muscle. As the pennation angle increases, the muscle fibres become shorter, and the number of fibres increases, resulting in a larger cross-sectional area.
Unipennate muscles have a diagonal fibre arrangement, which allows for great strength. However, due to the fibre angle, the maximum force in the direction of action is less than the maximum force in the fibre direction.
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Examples of unipennate muscles include the extensor digitorum longus and the extensor digitorum communis
A unipennate muscle is a type of skeletal muscle with fascicles that attach obliquely to its tendon. The tendon in a unipennate muscle extends along one side of the belly. If all the fascicles are on the same side of the tendon, the pennate muscle is called unipennate.
The extensor digitorum longus is a unipennate muscle situated at the lateral part of the front of the leg. It arises from the lateral condyle of the tibia, the upper three-quarters of the anterior surface of the body of the fibula, the upper part of the interosseous membrane, the deep surface of the fascia, and the intermuscular septa between it and the tibialis anterior on the medial, and the peroneal muscles on the lateral side. The extensor digitorum longus is the most lateral of all the muscles in the extensor compartment and lies laterally to the tibialis anterior and extensor hallucis longus.
The extensor digitorum communis, or extensor digitorum, is a muscle of the posterior forearm present in humans and other animals. It extends the phalanges, the wrist, and the elbow. It is the most superficial muscle of the posterior forearm and is located superficial to the abductor pollicis longus and extensor pollicis longus muscles.
The extensor digitorum longus and the extensor digitorum communis are examples of unipennate muscles.
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Unipennate muscles are stronger than bipennate or multipennate muscles
The strength of a muscle is determined by its architecture, which is the physical arrangement of muscle fibres at the macroscopic level. There are three main types of muscle architecture: parallel, pennate (also known as pinnate or penniform), and hydrostats.
Pennate muscles are further categorised into unipennate, bipennate, and multipennate muscles, depending on the number of similarly angled sets of fibres attached to the central tendon. In unipennate muscles, the fascicles are located on one side of the tendon, with muscle fibres oriented in a single direction. Bipennate muscles, on the other hand, have fascicles on both sides of the tendon, resembling the arrangement of a single feather. Multipennate muscles have fascicles that insert into multiple tendons, converging towards a common tendon.
Unipennate muscles are stronger than bipennate and multipennate muscles due to their larger physiological cross-sectional area (PCSA). PCSA is the total area of the cross-sections perpendicular to the muscle fibres, and it increases with the pennation angle and muscle length. In unipennate muscles, the pennation angle varies from 0° to 30°, resulting in a larger PCSA compared to bipennate and multipennate muscles. A larger PCSA leads to a greater force-generating capacity, making unipennate muscles stronger.
Additionally, unipennate muscles have shorter fibres compared to bipennate and multipennate muscles. As pennation increases from unipennate to multipennate, the muscle fibres become shorter. Shorter fibres contribute to increased muscle strength. This is because the speed at which a muscle fibre can shorten is influenced by its length—shorter fibres can contract more quickly, resulting in a stronger muscle.
Examples of unipennate muscles include the flexor pollicis longus, psoas minor, and extensor digitorum of the forearm. Bipennate muscles include the rectus femoris and gastrocnemius, while the deltoid muscle is an example of a multipennate muscle.
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Unipennate muscles are found in the hand and wrist
The hand and wrist are complex parts of the body, with a network of bones, muscles, nerves, connective tissue, and blood vessels. There are 34 muscles in each hand, which work with the muscles in the forearm to allow movement and dexterity. The forearm muscles that move the hand are grouped into flexor and extensor muscles. These muscles allow for flexion, extension, abduction, and adduction of the wrist.
The hand also has intrinsic muscles that allow for the movement of the fingers and fine adjustments for complex and precise tasks. These include the thenar muscles, which control the thumb, and the hypothenar muscles, which line the outer edges of the palm on the outside of the pinkie finger.
Unipennate muscles are a type of skeletal muscle with fibres attached obliquely to a tendon on one side. Unipennate muscles are found in the hand, such as the interossei muscles, which are located between the metacarpal bones of the hand. There are four dorsal and three palmar interossei muscles. The dorsal interossei allow us to spread our fingers apart, while the palmar interossei pull our fingers together.
The lumbrical muscles in the hand also have a unipennate structure. These muscles are positioned between the metacarpal bones and provide flexion in the metacarpophalangeal joint and extension in the interphalangeal joints.
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Unipennate muscles have a larger number of muscle fibres per unit
The increased number of muscle fibres in unipennate muscles has important implications for their function. Firstly, the greater number of fibres enables the muscle to generate more force. This increased force production is a result of the collective contraction of the individual muscle fibres working in unison. The architectural arrangement of unipennate muscles, with their unique fibre orientation, enhances their strength and capacity to exert force.
Additionally, the larger number of muscle fibres in unipennate muscles influences the speed of contraction. The length of muscle fibres plays a role in determining the velocity of their shortening during contraction. In unipennate muscles, as the pennation angle increases, the fibres become shorter. This shorter fibre length contributes to a relatively slower contraction speed compared to muscles with longer fibres. Therefore, the architectural characteristics of unipennate muscles, including the larger number of fibres and their shorter length, collectively influence the muscle's contractile properties.
The structure of unipennate muscles, with their distinct fibre arrangement, is particularly well-suited for certain functions. For example, the lateral gastrocnemius, a unipennate muscle, is responsible for supporting and propelling the weight of the body. The high force production capacity of unipennate muscles makes them ideal for such weight-bearing roles. Additionally, unipennate muscles are commonly found in the limbs, where they contribute to powerful movements such as flexion and extension. Examples of unipennate muscles include the flexor pollicis longus, extensor digitorum, and certain deep hand muscles.
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Frequently asked questions
Unipennate muscles have fibres that attach to one side of the tendon. This arrangement allows for great strength.
Some examples of unipennate muscles include the extensor digitorum longus, found in the lateral, lower leg, and certain muscles in the hand, such as the Lumbricals.
Unipennate muscles are a type of pennate muscle, which are a subtype of skeletal muscle. Pennate muscles have a large number of muscle fibres, allowing them to produce relatively more tension for their size compared to non-pennate muscles. However, they also tire more easily.
