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BIOLOGY · Stage 8 · Chapter 6: Nutrition, Health and Movement

Biology 6.10 Muscles and movement — Antagonistic Muscle Pairs

5 min read 6 parts Lesson 10 of 12

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Biology 6.10 Muscles and movement — Antagonistic Muscle Pairs — Alhussan International Academy — Biology (Stages 7–9) notes: Identify types of joint and explain how antagonistic muscles move the bones at a hinge joint.Joint — wherever two bones meet, and even a solid skeleton wou…

  • Ball-and-socket joints
  • Hinge joints
  • Fixed joints
  • Lubricating fluid
  • Contraction
  • Why a pair is needed

Section 1 of 6Joints make movement possible

  • Joint
    • wherever two bones meet, and even a solid skeleton would give protection and support but no movement without joints.
  • Ball-and-socket joints
    • they give all-round movement, as in the hips and shoulders.
  • Hinge joints
    • they allow forwards and backwards movement only, as in the elbows and knees.
  • Fixed joints
    • some joints allow no movement, such as the fused bones of the skull.
    • When a baby is born these skull joints are open, so the bones can move a little and the brain can grow.
    • Once the brain is fully grown the joints close (fuse) to protect it.

Section 2 of 6Structures in joints

  • Ligaments
    • they hold the bones in a joint in place but allow them to move, and are slightly stretchy but very strong.
  • Cartilage
    • smooth, rubbery tissue covering the bone ends in hinge and ball-and-socket joints.
    • It cushions the bones and reduces friction, protecting the bone ends from wearing away.
  • Lubricating fluid
    • joints that move a lot make a fluid that keeps the cartilage wet and slippery, so the bones move without rubbing.
  • Tendons
    • strong tissues that join muscles to bones and do not stretch.

Section 3 of 6How muscles produce movement

  • Bones
    • bones cannot move by themselves, and movement at joints is produced by muscles.
  • Contraction
    • when a muscle contracts (shortens) it pulls on the bone and moves it, with the joint acting as a pivot.
  • Pull only
    • muscles can only pull and cannot push.
  • Relaxing
    • a relaxed muscle does not move a bone and must be pulled back to its original length by another muscle.
  • Energy
    • muscle contraction needs energy from respiration, so working muscles need glucose and oxygen.

Section 4 of 6Antagonistic pairs

  • Antagonistic muscles = a pair of muscles working in opposite ways, so that when one contracts the other relaxes.
  • Why a pair is needed
    • each joint needs at least two muscles, one to bend it and one to straighten it again.
  • Elbow
    • the biceps and triceps (back) work as a pair at this hinge joint.
      • (front of the upper arm)
MovementMuscle contractingMuscle relaxing
Bending the elbowBicepsTriceps
Straightening the elbowTricepsBiceps
  • Other pairs
    • at the knee the hamstring bends the leg and the quadriceps straightens it.

Section 5 of 6Bending and straightening the arm

  1. Nerve impulses from the brain reach the biceps.
  2. The biceps contracts, getting shorter and thicker, and pulls on the bones of the lower arm through its tendon.
  3. The triceps is relaxed and stretched thin, so the arm bends upwards.
  4. To straighten the arm, the triceps contracts and pulls the arm downwards.
  5. At the same time the biceps relaxes, and is pulled long and thin again.
  • Lever
    • the forearm acts as a lever with the elbow joint as the pivot.

Section 6 of 6Muscles, health and fitness

  • Exercise
    • regular exercise increases muscle size and strength and makes joints and bones stronger, while unused muscles become weaker.
  • Injuries
    • torn muscles, and sprains when ligaments are overstretched.
  • Nutrition
    • protein is needed to build muscle and calcium supports bones.

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