3 types of muscles are contained within the human body:
- Smooth
- Cardiac
- Skeletal
Smooth muscles are found in the walls of many organs, such as the stomach and in blood vessels. They have a non-striated appearance and contract involuntarily.
Cardiac muscles are found in the walls of the heart. They also contract involuntarily, but have a striated appearance.
Skeletal muscles are attached to, and move, bones. These muscles contract voluntarily and have a striated appearance. Skeletal muscles are sub-categorized into 4 distinct groups, based on the orientation and arrangement of the muscle fibres:
- Parallel skeletal muscles consist of fibres that are arranged in parallel to the line pulled during contraction. Parallel muscles can be sub-categorized based on their shape, into:
- Quadrilateral (eg. the pronatur quadratus)
- Strap-like (eg. the sartorius)
- Fusiform (eg. the brachioradialis)
- Convergent muscles contain fibers that have a wide origin, but converge in order to attach to a narrow tendon.
- Circular skeletal muscles are made up of fibers that are arranged in a circular manner. They are found at points of openings, where contraction leads to a closure of that opening.
- Pennate skeletal muscles consist of muscle fibres that are attached to the sides of a tendon, in a manner that is similar to a feather. Pennate muscles can be sub-categorized based on their shape into:
- Unipennate (eg. the flexor policis longus)
- Bipennate (eg. the rectus femoris)
- Multipennate (eg. the deltoid)
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