Muscles & Movement

• Muscles pull on bones to produce movement — they cannot push bones apart.
• Voluntary muscles (arm, leg) vs involuntary (heart, digestion) — intro level.
• Pairs of muscles — biceps bends elbow, triceps straightens it.
• How muscles, bones, and joints work together as a movement system.

Level 1 — Muscles pull bones

Verbal: When a muscle contracts (shortens), it pulls the bone at the joint; relaxation lets opposite movement occur.

Visual (arm bend):

Tendons: Strong cords attaching muscle to bone.

Antagonistic pair: Biceps and triceps work opposite — one contracts, other relaxes.

Level 2 — Voluntary, involuntary, and fitness

Voluntary: You control — smile, kick, write.

Involuntary: Automatic — heart beats, food moves in stomach (smooth muscles).

Facial muscles: Many small muscles for expression.

Exercise: Makes voluntary muscles stronger; warm-up prevents pulls.

No movement without joints: Muscle contraction + joint pivot = visible motion.

Earthworm vs human: Muscles in worm body wall; human has skeletal muscles on bones.

Explain arm movement when picking up a book.

Step 1 — Brain signal → biceps voluntary muscle contracts
Step 2 — Tendon pulls radius/ulna bones at elbow hinge joint
Step 3 — Forearm rises; triceps relaxed
Step 4 — To lower book, triceps contracts, biceps relaxes

• Do muscles push or pull bones?
• Name the muscle pair that moves the upper arm at the elbow.
• Give one example each of voluntary and involuntary muscle action.
• What connects muscle to bone?

Open the Practice tab for graded questions on Muscles & Movement.