Anatomy: Joints and Muscle Connections

Joint Connections

• A connection of bones in a joint is called an articulation.
• Ligaments connect bones to bones.
• Tendons connect muscles to bones.
• Aponeurosis is a flat sheet of tendon that connects muscles.

Joint Types

• Diarthrodial joints are freely movable joints.
• Synarthrodial joints are immovable joints.
• Amphiarthrodial joints have limited movement.

Diarthrodial Joint Subtypes

• Hinge
• Ball and Socket

Muscle Attachments

• Tendons attach muscles to bones.
• The origin is the less movable end of a muscle, typically more proximal.
• The insertion is the more movable end of a muscle, typically more distal, where the action occurs.

Muscle Structure - Pennate Muscles

• Some muscles have a pennate arrangement, where muscle fibers are positioned obliquely to the central tendon.
• Pennate muscles have a different structure that influences force and velocity.

Muscle Contractions

• Isometric contraction: Muscle develops tension but does not change length.
• Concentric contraction: Muscle shortens while developing tension. This is associated with movement in the direction of the power stroke.
• Eccentric contraction: Muscle lengthens while developing tension. This is usually used to control speed or prevent an object from moving further.
• Isotonic contraction: This includes both concentric and eccentric contractions, involving muscle shortening or lengthening.

Muscle Actions

• Agonist muscles are the muscles primarily responsible for a movement.
• Antagonist muscles oppose the action of the agonist.

Stabilizer Muscles

• Stabilizer muscles contract to maintain posture or a position of a joint that another muscle crosses or works on two joints when a muscle crosses more than one joint - this is to prevent or limit movement at one joint while the other joint is moving.