Overview
This lecture explains the vocabulary of muscle attachments and actions, detailing how skeletal muscles connect to bones and produce various body movements.
Muscle Attachments: Origins and Insertions
- Skeletal muscles usually attach to bones at two points: origin and insertion.
- The origin is the attachment site on the immobile bone during movement.
- The insertion is the attachment site on the bone that moves during an action.
- Example: Triceps brachii has three origins (on scapula and humerus) and one insertion (on ulna).
Major Types of Muscle Actions
- Muscles act on synovial joints to produce movements.
- Flexion: Bending; decreases the angle between two bones (e.g., elbow bending).
- Extension: Straightening; increases the angle between bones (e.g., elbow straightening).
- Abduction: Moves a limb away from the body's midline (e.g., lifting arm to the side).
- Adduction: Moves a limb toward the body's midline (e.g., lowering arm to the side).
- Pronation: Rotates forearm so the palm faces downward or backward.
- Supination: Rotates forearm so the palm faces upward or forward.
- Elevation: Moves a body part upward (e.g., closing jaw).
- Depression: Moves a body part downward (e.g., opening jaw).
- Protraction: Moves a bone forward without changing its angle (e.g., jutting jaw out).
- Retraction: Moves a bone backward without changing its angle (e.g., pulling jaw in).
- Inversion: Turns sole of the foot inward.
- Eversion: Turns sole of the foot outward.
- Dorsiflexion: Lifts foot upward toward the shin.
- Plantar flexion: Points foot downward.
Roles of Muscles in Movement
- Prime mover (agonist): Main muscle responsible for producing a movement.
- Antagonist: Muscle that opposes or reverses the prime mover's action.
- Synergist: Muscle that helps the prime mover perform its action.
- Stabilizer: Muscle that holds bones steady during movement.
Key Terms & Definitions
- Origin — attachment site on the stationary bone.
- Insertion — attachment site on the moving bone.
- Prime mover (agonist) — muscle chiefly responsible for a specific movement.
- Antagonist — muscle that opposes the action of the prime mover.
- Synergist — muscle assisting the prime mover.
- Stabilizer — muscle keeping a bone or joint stable during movement.
Action Items / Next Steps
- Review muscle movement animations and practice identifying origins and insertions on diagrams.
- Complete the Body Motions Lab Activity if provided by your instructor.