Muscle System Lab

The big idea: most muscle names are not random. They are made of Latin or Greek word parts, and each part is a clue. Read the clues and you can often say where a muscle is and what it does before you ever memorize it. There are seven kinds of clues.

Worked example: flexor carpi radialis

Put it together: a muscle on the radius (thumb) side of the forearm that flexes the wrist. That's exactly where and what it is. Ready? Press Play: crack the case.

The forearm flexes and relaxes. Watch the biceps shorten and the triceps lengthen.

Three words for every muscle

Origin (O)The attachment that usually stays still. It is often the more proximal one, closer to the trunk.

Insertion (I)The attachment on the bone that moves. It is usually more distal.

Action (A)When a muscle contracts, it pulls the insertion toward the origin. Muscles only pull. They never push.

Think of it like thisA muscle is a rope tied between two bones. The origin is tied to a post. The insertion is tied to a door. Pull the rope, and the door swings toward the post.

Muscles work in teams

Prime mover (agonist)The main muscle that makes a movement. Elbow flexion: the biceps brachii.

AntagonistDoes the opposite movement. It relaxes and lengthens while the prime mover works, and helps control the motion. Elbow flexion: the triceps brachii.

SynergistHelps the prime mover, adding force or steadying the motion. Elbow flexion: the brachialis.

FixatorA synergist that holds the prime mover's origin still. Muscles that steady the scapula while the arm moves are fixators.

Prime movers and antagonists usually sit on opposite sides of a joint: biceps and triceps, quadriceps and hamstrings, tibialis anterior and gastrocnemius.

Muscle System Lab

Worked example: flexor carpi radialis

Body map

The parts of every lever

Three words for every muscle

Muscles work in teams