Logan Steele
Fusiform muscles are a type of skeletal muscle that is spindle-shaped, with a wide center that tapers down to narrow ends. The muscle fibers in a fusiform muscle are arranged in a parallel fashion and run the entire length of the muscle. Examples of fusiform muscles include the biceps brachii, which flexes the elbow and supinates the forearm. The gastrocnemius, which is made principally of fast-twitch type II fibers, is another example of a fusiform muscle.
| Characteristics | Values |
|---|---|
| Shape | Spindle-shaped, wider in the middle and narrow at both ends |
| Muscle fibres arrangement | Parallel fashion, running the entire length of the muscle |
| Muscle belly | Expanded |
| Force | Concentrated into a small area |
| Range of motion | Quick and wide |
| Muscle architecture | Parallel |
| Examples | Biceps brachii, gastrocnemius |
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Muscle shape
Fusiform muscles are spindle-shaped, with a wide centre that tapers down to narrow ends. The muscle fibres in a fusiform muscle are arranged in a parallel fashion and run the entire length of the muscle. The line of action in this muscle type runs in a straight line between the attachment points, which are often tendons. Due to their shape, fusiform muscles produce a force that is concentrated into a small area. Examples of fusiform muscles include the biceps brachii, which flexes the elbow and supinates the forearm, and the gastrocnemius, which is made principally of fast-twitch type II fibres.
Parallel muscles are typically long, thin muscles that do not have much strength. They have a larger central region called a muscle belly that tapers to tendons on each end. An example of a parallel muscle is the sartorius muscle, which runs down the thigh to the knee.
Circular muscles are striated muscles that form a circular shape. They include the orbicularis oris, the muscle surrounding the mouth, and the orbicularis oculi, the muscles surrounding the eyes.
Convergent muscles are fan-like, triangular-shaped muscles that attach to a fixed bone. They have a weaker pull on the attachment site compared to other parallel fibres due to their broad nature. An example of a convergent muscle is the pectoralis major, the breast muscle situated on the chest.
Pennate muscles (or penniform muscles) are feather-like muscles whose muscle fibres attach in a slanted position to the tendon. They are typically shorter than fusiform muscles and can insert onto tendons in several different manners, forming uni-, bi-, or multipennate muscles. Examples of pennate muscles include the extensor digitorum longus, found in the lateral lower leg, and the rectus femoris, a bipennate quadricep muscle that flexes the hip.
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Muscle fibre arrangement
The fusiform arrangement makes up most human muscle, with the fibres largely arranged in parallel arrays along the muscle’s longitudinal axis with tendons at the proximal and distal ends. The muscle fibres in a fusiform muscle are arranged in a parallel fashion and run the entire length of the muscle. Fusiform fibres can largely run parallel, converge or form a circular arrangement.
Parallel muscles have fascicles that are arranged in the same direction as the long axis of the muscle. The majority of skeletal muscles in the body have this type of organisation. Some parallel muscles are flat sheets that expand at the ends to make broad attachments. Parallel and circular muscles are typically long, thin muscles that do not have much strength.
In contrast, pennate muscles are feather-like muscles whose muscle fibres attach in a slanted position to the tendon. Due to this design, the muscle fibres in a pennate muscle can only pull at an angle, and as a result, they do not move their tendons very far. Pennate muscle fibres are typically shorter than those of a fusiform muscle.
Convergent muscles are fan-like, triangular-shaped muscles that attach to a fixed bone. They have a weaker pull on the attachment site compared to other parallel fibres due to their broad nature. These muscles are considered versatile because of their ability to change the direction of pull depending on how the fibres are contracting.
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Muscle function
Fusiform muscles are a type of parallel muscle, with fibres that run parallel to the force-generating axis. They are spindle-shaped, with a wide centre that tapers down to narrow ends. The muscle fibres run the entire length of the muscle, often with tendons at the proximal and distal ends. The force produced by fusiform muscles is concentrated into a small area. This shape allows for a great degree of shortening, enabling the muscle to produce quick and wide ranges of motion. Examples of fusiform muscles include the biceps brachii, which flexes the elbow and supinates the forearm.
Penniform muscles, in contrast, are feather-like muscles whose fibres attach in a slanted position to the tendon. Due to this design, the muscle fibres in a penniform muscle can only pull at an angle, and as a result, they do not move their tendons very far. There are three subdivisions of penniform muscles: unipennate, bipennate, and multipennate. An example of a unipennate muscle is the extensor digitorum longus, found in the lateral lower leg. The rectus femoris, a quadricep muscle that flexes the hip, is an example of a bipennate muscle. The deltoid, the large muscle over the shoulder joint, is an example of a multipennate muscle.
Convergent muscles are fan-like, triangular-shaped muscles that attach to a fixed bone. They are considered versatile due to their ability to change the direction of their pull depending on how the fibres are contracting. An example of a convergent muscle is the pectoralis major, the breast muscle situated on the chest.
Circular muscles are striated muscles that form a circular shape. They concentrically contract and relax to decrease and increase the size of the opening they surround. The orbicularis oris, the muscle surrounding the mouth, and the orbicularis oculi, the muscles surrounding the eyes, are examples of circular muscles.
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Muscle types
The human body has over 600 muscles, which can be categorised into three types: skeletal, cardiac, and smooth.
Skeletal Muscles
Skeletal muscles are attached to bones and give the body structure and strength. They are voluntary muscles, meaning we control their movements. Skeletal muscles come in many different sizes and shapes, with several subtypes, including:
- Circular muscles, which are striated muscles that form a circular shape, such as the orbicularis oris (around the mouth) and orbicularis oculi (around the eyes).
- Parallel muscles, which are typically long and thin without much strength. An example is the sartorius muscle, which runs down the thigh to the knee.
- Convergent muscles, which are fan-like and triangular, attaching to a fixed bone. An example is the pectoralis major, the breast muscle.
- Fusiform muscles, which are spindle-shaped with a wide centre that tapers down to narrow ends. Examples include the biceps brachii and gastrocnemius. Fusiform muscles have fibres arranged in parallel and can run parallel, converge, or form a circular arrangement.
- Pennate muscles (or penniform muscles), which are feather-like with fibres attaching slantingly to the tendon. Examples include the extensor digitorum longus (unipennate), rectus femoris (bipennate), and deltoid (multipennate).
Cardiac Muscles
Cardiac muscles comprise the walls of the heart, allowing blood to be pumped through the vasculature. They are involuntary muscles, meaning their contractions are not under conscious control. There are two types of cardiac muscle cells: autorhythmic, which set the pace of contraction, and contractile (cardiomyocytes), which constitute most of the heart muscle and can contract.
Smooth Muscles
Smooth muscles are usually found in sheets or layers and are also involuntary. They are found throughout the body, including in the blood vessels, gastrointestinal tract, bronchioles, uterus, and bladder. Smooth muscles contract and relax to push food through the digestive system and can be further classified into single-unit and multiunit types. Single-unit smooth muscles are found in the gut and blood vessels, while multiunit smooth muscles are found in the muscles of the eye and at the base of hair follicles.
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Muscle architecture
There are several different muscle architecture types, including parallel, pennate, and hydrostats. The architecture type is determined by the direction in which the muscle fibres are oriented relative to the force-generating axis. The force produced by a given muscle is proportional to the cross-sectional area, or the number of parallel sarcomeres present. The parallel muscle architecture is found in muscles where the fibres are parallel to the force-generating axis. Parallel muscles are typically long, thin muscles that do not have much strength. An example of a parallel muscle is the sartorius muscle, which runs down the thigh to the knee.
Pennate muscles (also known as penniform or pinnate muscles) are feather-like muscles whose muscle fibres attach in a slanted position to the tendon. There are three subdivisions of pennate muscles: unipennate, bipennate, and multipennate. Unipennate muscles are those where the muscle fibres are oriented at one fibre angle to the force-generating axis and are all on the same side of a tendon. An example of this muscle architecture is the lateral gastrocnemius. Muscles that have fibres on two sides of a tendon are considered bipennate. The rectus femoris of the quadriceps is an example of a bipennate muscle. The third type of pennate subgroup is known as the multipennate architecture, where muscles have fibres that are oriented at multiple angles along the force-generating axis. The deltoid muscle in the shoulder of humans is an example of a multipennate muscle.
A third muscle architecture type, muscular hydrostats, can also be considered. Muscular hydrostats function independently of a hardened skeletal system.
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Frequently asked questions
Fusiform means spindle-shaped, with a wide middle that tapers down to narrow ends.
Examples of fusiform muscles include the biceps brachii, which flexes the elbow and supinates the forearm, and the gastrocnemius, which is made principally of fast-twitch type II fibres.
Fusiform muscles are arranged in a strap-like fashion to provide the greatest degree of shortening, thus enabling the muscle to produce a quick and wide range of motion. The muscle fibres in a fusiform muscle are arranged in a parallel fashion and run the entire length of the muscle.
Due to the shape of fusiform muscles, the force produced is concentrated into a small area.
