Chap 1 : Joints & Muslces

Joints

• Definition of Joints:
  The place where bones meet is called a joint.
• Types of Joints Based on Movement:
  • Immovable Joints: In some joints, such as those in the skull, the bones are fused together and cannot move.
  • Movable Joints: Most joints, however, allow some movement.
• Hinge Joints:
  • Some joints, such as the elbow or knee, are called hinge joints because the movement is like the hinge on a door.
  • The bones in hinge joints can only move forwards or backwards.
  • Examples of Hinge Joints: Two examples of the hinge joint are the elbow joint and the knee joint.
• Ball-and-Socket Joints:
  • A few joints, such as the hip and shoulder joints, are called ball-and-socket joints because the end of one bone forms a round structure, like a ball, that fits into a cup-shaped socket.
  • This structure allows movement backwards and forwards, from side to side, and even circular movement, as when you move your arm in a circle.
  • Examples of Ball-and-Socket Joints: Two examples of the ball-and-socket joint are the hip joint and shoulder joint.

Muscles in a Hinge Joint

1. How Muscles Produce Movement

• Muscle action produces movement across a hinge joint.
• To understand this, we need to examine what happens beneath the skin.
• Muscle Structure & Function:
  • Muscle is made up of tissue that can contract (shorten) to generate movement.
  • A muscle is attached to two bones across a joint.
  • When a muscle contracts, it exerts a pulling force, moving one bone while the other remains stationary.
• Example: The Biceps Muscle
  • The biceps muscle in the upper arm is attached to:
    • The shoulder blade (scapula)
    • The radius bone in the forearm
  • When the biceps contracts, it pulls on the radius, raising the forearm.

2. Antagonistic Muscle Pairs

• Muscles Cannot Lengthen Themselves:
  • A muscle cannot extend on its own; it requires an opposing force to stretch it.
  • This force is provided by another muscle working in opposition.
• Example: Biceps & Triceps (Antagonistic Pair)
  • Triceps Muscle Structure:
    • Attached to:
      • The shoulder blade (scapula)
      • The humerus (upper arm bone)
      • The ulna (forearm bone)
  • Mechanism of Movement:
    • When the triceps contracts, the biceps relaxes, and the force exerted by the triceps:
      • Lengthens the biceps
      • Pulls the forearm down
    • When the biceps contracts, the triceps relaxes, and the force exerted by the biceps:
      • Lengthens the triceps
      • Raises the forearm
  • Summary of Antagonistic Action:
    • Biceps contracts, triceps relaxes → Lower arm raised.
    • Biceps relaxes, triceps contracts → Lower arm lowered.
• Definition of Antagonistic Muscle Pair:
  • Two muscles that work in opposition to produce movement in opposite directions.

BOOK QUESTIONS

Q1. State three important functions of the skeleton.

1. Support – Gives shape to the body and holds it upright.
2. Protection – Shields delicate organs (e.g., skull protects the brain, ribs protect the heart and lungs).
3. Movement – Works with muscles to allow body parts to move.

Q2. How can you tell a muscle from a bone?

• Muscle: Soft, can contract (shorten) and relax (lengthen), helps in movement.
• Bone: Hard, rigid, does not bend or stretch, provides structure.

Q3. How do pairs of muscles make a bone move?

• Muscles work in pairs (antagonistic muscles) where one contracts while the other relaxes.
• Example: When biceps contract, the triceps relax, pulling the forearm up.
• When triceps contract, the biceps relax, pulling the forearm down.

Q4. Name two hinge joints.

1. Elbow joint (between upper and lower arm).
2. Knee joint (between thigh and lower leg).

Q5. Name two ball-and-socket joints.

1. Shoulder joint (where arm connects to shoulder).
2. Hip joint (where leg connects to hip).

Q6. How is a hinge joint different from a ball and socket joint?

Q7. When biceps contract, what happens to:

1. Triceps → They relax.
2. Lower arm → It raises up.

Q8. What do you understand by the term “pair of antagonistic muscles”?

• Two muscles that work in opposite ways to move a bone.
• When one contracts, the other relaxes, allowing movement in two directions.
• Example: Biceps & triceps in the arm.