Skeletal & Muscular System
🦴 The Skeletal System
The human skeleton is made up of 206 bones in adults. It plays five key roles:
Support: It forms the body’s frame and supports tissues and organs.
Protection: Bones protect internal organs. For example, the skull protects the brain, the ribcage protects the heart and lungs, and the vertebrae protect the spinal cord.
Movement: Bones and joints allow movement, especially when muscles pull on them.
Blood cell production: The bone marrow, found inside large bones like the thigh and hip, produces red and white blood cells.
Mineral storage: Bones store important minerals such as calcium and phosphorus, which can be released into the bloodstream when needed.
🦴 Bones come in different types:
Long bones (e.g. femur) help with movement.
Flat bones (e.g. ribs, sternum, skull) protect organs.
Short bones (e.g. wrist and ankle) provide stability and movement.
Irregular bones (e.g. vertebrae) have complex shapes.
Bones are living tissue, with a hard outer layer for strength and a soft, spongy inner layer that contains marrow. They have a blood supply, which helps with growth and healing.
🤸♀️ Joints and Movement
Where two or more bones meet, we call it a joint. Some joints allow movement, while others (like the ones in the skull) are fixed. Types of joints include:
Hinge joints (elbow, knee) – move in one direction, like a door.
Ball-and-socket joints (shoulder, hip) – allow movement in many directions.
Fixed joints – no movement (e.g. skull).
Ligaments connect bone to bone and help stabilize joints.Tendons connect muscles to bones and allow movement when muscles contract.
💪 The Muscular System
The muscular system works with the skeleton to allow movement, maintain posture, and support body functions.
There are three types of muscle:
Skeletal muscles – attached to bones and under your control. They help you move arms, legs, fingers, etc.
Cardiac muscle – found in the heart. It contracts continuously to pump blood.
Smooth muscle – found in organs like the stomach and blood vessels. It works automatically (involuntarily).
Muscles always pull, never push. To move a limb, muscles work in pairs:
One contracts (shortens), the other relaxes (lengthens).
These pairs are called antagonistic muscles.
🧩 How Muscles and Bones Work Together
Movement happens when a muscle contracts and pulls on the bone it's attached to via a tendon. For example, to bend your elbow, the biceps contract and pull, while the triceps relax.
This team effort is what helps you:
Walk
Write
Sit upright
Balance
Breathe and more!
⚠️ Common Misunderstandings
❌ Bones are not dead! They’re living tissues filled with blood vessels and cells.
❌ Muscles don’t push bones — they only pull.
❌ Not all joints move — some are fixed to protect the brain.
❌ The heart is not made of skeletal muscle; it’s made of cardiac muscle.
Top tips:
🔄 Bones + muscles = movement: They always work as a team!
🧠Skull protects the brain, ribcage protects the lungs and heart, spine protects the spinal cord.
🧬 Bone marrow is your body’s blood cell factory.
💪 Muscles only pull, so they work in antagonistic pairs.
🧵 Remember: Tendons = muscle to bone, Ligaments = bone to bone.
🦴 Keep your bones strong by getting calcium (from milk, yogurt, greens) and staying active.
🧘 Posture and balance are controlled by muscles constantly adjusting against gravity.