The more stationary site of muscle attachment is called the __ and the more moveable site of muscle attachment is called the ———-. When skeletal muscles contract across a diarthrosis, the ———– moves toward the ————–.
The correct answer and explanation is :
The more stationary site of muscle attachment is called the origin, and the more moveable site of muscle attachment is called the insertion. When skeletal muscles contract across a diarthrosis, the insertion moves toward the origin.
Explanation:
Skeletal muscles function by generating force and movement through contraction. To understand muscle movement, it is essential to differentiate between two primary points of muscle attachment: origin and insertion.
- Origin:
- The origin of a muscle is the fixed or less movable attachment site.
- It typically lies on a more stable bone, which does not move significantly during muscle contraction.
- In most cases, the origin is located proximally (closer to the body’s center).
- Insertion:
- The insertion is the more moveable attachment site of the muscle.
- It is usually on a bone that moves when the muscle contracts.
- It tends to be located distally (further from the body’s center).
Movement Across a Diarthrosis (Freely Movable Joint):
A diarthrosis is a type of synovial joint that allows free movement, such as the shoulder, knee, or elbow joint. When a skeletal muscle contracts, it pulls on the insertion, causing movement toward the origin.
For example:
- In the biceps brachii muscle, the origin is on the scapula, and the insertion is on the radius (forearm bone).
- When the biceps contract, the forearm moves toward the upper arm, demonstrating the movement of the insertion toward the origin.
This fundamental principle of muscle mechanics applies to all voluntary movements in the body, enabling actions like walking, lifting, and grasping objects.
