Logan Steele
The human body has over 600 muscles, which help us do everything from breathing to running marathons. These muscles are attached to bones via tendons, with most muscles having at least one origin point and one insertion point. The origin is the end of the muscle that attaches to the stable base, or proximal bone, while the insertion is the end that attaches to the moving bone, or distal bone. For example, the biceps have two origin points on the scapula, or shoulder blade, and one insertion point on the radius, or forearm bone.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | Over 600 |
| Muscle attachments | Bones, tendons |
| Muscle movements | Flexion, extension, abduction, adduction, elevation, depression, supination, pronation, dorsiflexion, plantar flexion |
| Muscle types | Prime movers, antagonists, synergists, fixators, skeletal, cardiac, smooth |
| Muscle shapes | Delta or triangular, serrated or saw-like, rhombus or diamond |
| Muscle names | Named based on location, origin, insertion, number of origins, shape, size, direction, function |
| Muscle functions | Moving the body, keeping internal organs functioning |
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What You'll Learn
Muscles attach to bones via tendons
The human body has over 600 muscles, and skeletal muscles make up between 30% and 40% of our total body mass. These muscles are located between the bones and consist of flexible muscle fibres that contract, allowing us to move. Muscles attach to bones via tendons or fibrous connective tissues. Tendons are mostly made of collagen, one of the most abundant proteins in the human body. They also contain blood vessels and nerves.
Tendons are stiffer than muscles but have great strength. For example, the flexor tendons in the foot can handle more than eight times the body weight. Tendons work as levers to move bones as muscles contract and relax. When a muscle contracts, the tendon pulls the attached bone, causing it to move. Tendons can be found all over the body, from the head down to the toes. For instance, the biceps brachii is a muscle located on the front of the upper arm between the shoulder and elbow. It attaches to the upper part of the radius, the forearm bone on the thumb side of the arm, via tendons.
The triceps brachii is another muscle located at the back of the arm. It attaches to the scapula and extends to the ulna at the back of the elbow. The brachialis muscle runs from half of the humerus to the ulna, the forearm bone on the pinky finger side of the arm. The pronator quadratus is a small square-shaped muscle that connects the lower end of the ulna to the lower end of the radius near the wrist.
The prime mover or agonist is the muscle that provides the primary force for a movement. An antagonist muscle opposes the prime mover by providing resistance or reversing the movement. Synergist muscles assist the prime mover and help stabilise a movement. They often connect to the same bones as the agonist. Fixator muscles assist in movement by holding the origin stable.
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The origin is the attachment to the stable bone
The human body has over 600 muscles, which help us do everything from breathing and running to holding our bodies still. These muscles are attached to bones via tendons. The origin is the attachment to the stable bone, which doesn't move much or at all when the muscle is contracted. This is usually the proximal bone. The insertion is the attachment to the moving bone, which is usually the distal bone.
For example, the bicep has two origin points, which lead to two "heads", where the name "biceps" comes from. These two tendons attach to the scapula, or shoulder blade. When the bicep is contracted, the elbow bends and the forearm moves closer to the upper arm. The radius, the forearm bone, is the distal bone and is the insertion point for the bicep. The scapula, in this case, is the stable bone and the origin.
The psoas major muscle is another example. The origin of this muscle is considered to be the body of vertebrae T12 through L5, and the insertion is on the lesser trochanter of the femur. The psoas major acts to flex the hip joint, bringing the thigh toward the torso. In this case, the vertebrae are the stable bone and the origin, while the femur is the moving bone and the insertion.
The piriformis muscle is an example of how the origin and insertion can change depending on the position of the body. From an anatomical position, the piriformis muscle externally rotates the hip. However, when the hip joint is flexed more than 90 degrees, the piriformis acts to internally rotate the hip. In this case, the origin and insertion have switched, as the position of the bones in relation to one another has changed.
The trapezius, or "traps", is a large, triangular pair of muscles that move the shoulder and the skull and neck. The medial (inside) part of the traps is the origin, as the stable base is the spine, while the insertion points converge around the scapula and clavicle, the moving bones.
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The insertion is the attachment to the movable bone
The human body has over 600 muscles, which help us do everything from breathing to running marathons. Skeletal muscles are part of the musculoskeletal system and work with bones, tendons, and ligaments to support our weight and move us. Tendons attach skeletal muscles to bones, and muscles are named based on their location, origin, insertion, number of origins, shape, size, direction, and function.
Another example is the psoas major muscle, which, from an anatomical position, originates in the body of vertebrae T12 through L5 and inserts on the lesser trochanter of the femur. The psoas major acts to flex the hip joint, bringing the thigh toward the torso. However, if you are lying down and lift one leg toward your torso, you are moving the insertion toward the origin. Similarly, if you are sitting up, you are bringing your spine toward your femur.
The piriformis muscle is another example of how muscle actions can change depending on the position of the body. From an anatomical position, the piriformis muscle externally rotates the hip. However, when the hip joint is flexed more than 90 degrees, the piriformis muscle acts to internally rotate the hip.
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Muscles can have multiple insertion points
In biology, muscles can have more than one insertion point, allowing them to exert force on different parts of the body. An insertion point is the place where a muscle attaches to a bone or other structure. Some muscles have multiple tendon insertions. For example, the biceps muscle in the upper arm has two insertion points on the radius bone in the forearm and the scapula bone in the shoulder. The triceps brachii has four points of attachment: one insertion on the ulna and three origins (two on the humerus and one on the scapula).
The Trapezius (Traps) is another example of a muscle with multiple insertion points. Each trap muscle is large enough to be divided into three sections: superior (upper) fibres, middle fibres, and inferior (lower) fibres. Each of these three sections has multiple origin points and multiple insertion points. The traps move the shoulder and the skull and neck. However, the main role of the traps is to move the shoulder.
The biceps brachii is another muscle with two insertion points. The insertion point is found on the distal bone, the radius, which is affected the most by the contraction. The coracobrachialis is the only muscle in the upper arm that does not connect to the forearm bones. Instead, it attaches to the humerus.
The brachioradialis muscle starts at the end of the humerus and runs the length of the forearm to a bony prominence at the wrist called the radial styloid process. The pronator quadratus is a small square-shaped muscle that connects the lower end of the ulna horizontally to the lower end of the radius near the wrist.
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Fixator muscles hold the origin stable to assist movement
The human body has over 600 muscles, each with an origin and an insertion. The insertion is the end of the muscle that attaches to the bone being pulled, while the origin is the end of the muscle attached to a fixed or stabilised bone. The prime mover, or agonist, is the muscle that provides the primary force driving the action. Antagonists, on the other hand, are in opposition to the prime mover, providing resistance or reversing the movement.
Synergists are muscles that assist the prime mover in its role. One type of synergist is the fixator muscle, which holds the origin stable to assist movement. Fixator muscles work alongside prime movers and synergists to enhance overall movement efficiency. They provide stability during muscle contractions, preventing strain and allowing smoother motions. For example, during a bicep curl, the muscles around the shoulder act as fixators, stabilising the shoulder joint while the biceps muscle contracts to lift the weight. Similarly, when performing a squat, the muscles around the core and hips act as fixators to keep the torso erect while the legs perform the primary lifting.
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Frequently asked questions
The insertion is the end of the muscle that attaches to the moving bone when the muscle is contracted.
The origin is the end of the muscle that attaches to the stable base which doesn't move when the muscle is contracted. The insertion is the end that attaches to the moving bone.
Tendons attach skeletal muscles to bones.
