The Musculoskeletal System of Humans

Functions of bones

• Bones provide support, forming a rigid internal framework that holds the body upright and gives it shape.
• Bones provide protection for delicate organs, the skull encloses the brain, the ribcage encloses the heart and lungs, and the vertebrae enclose the spinal cord.
• Bones allow movement by acting as rigid levers that muscles pull against across a joint.
• Bone marrow inside certain bones produces blood cells, and bones also store minerals such as calcium.

Types of joints

Muscles, tendons and ligaments

Muscles produce the force for movement by contracting, but they can only pull, never push. A tendon is a tough, non-elastic band that connects a muscle to a bone, so that when the muscle contracts, it pulls directly on the bone.

A ligament is different: it connects one bone to another at a joint, holding the bones in place while still allowing controlled movement and helping to prevent the joint from moving too far or dislocating.

How it is examined

Exam questions on this standard often ask you to label a diagram of a joint or the arm, to name the type of a given joint from its range of movement, or to distinguish a tendon from a ligament using their connections (muscle-to-bone versus bone-to-bone). You should also be able to link a bone's function, support, protection or movement, to its position in the body.

Inside a synovial joint

A movable joint such as the elbow or knee is called a synovial joint, and several features work together to let it move smoothly. Smooth, slippery cartilage covers the end of each bone where it meets another bone, reducing friction as the bones move against each other.

The whole joint is enclosed in a joint capsule, which contains synovial fluid, a thick, oily liquid that lubricates the joint and further cushions the bone ends. Ligaments cross the outside of the joint capsule, binding the bones together so the joint stays correctly aligned and does not dislocate during normal movement.

More joint types

Common labelling errors

Worked exam-style question

Question. A diagram shows the knee joint, with the ends of the femur and tibia covered by a smooth tissue, surrounded by a fluid-filled capsule, and held together by bands of tissue crossing the joint on the outside. (a) Name the smooth tissue covering the bone ends, and state its function.

(b) Name the fluid inside the joint capsule, and state its function. (c) Name the bands of tissue holding the bones together, and state one way they differ from a tendon.

Model answer. (a) The smooth tissue is cartilage; it reduces friction between the bone ends as the joint moves. (b) The fluid is synovial fluid; it lubricates the joint and cushions the bone ends.

(c) The bands are ligaments; unlike a tendon, which connects muscle to bone, a ligament connects bone to bone.

Practice question

A patient injures the band of tissue connecting the femur to the tibia at the knee, and the doctor explains that the knee now feels 'unstable' and moves further than normal in some directions. Name the type of structure most likely injured, and explain why this injury would cause instability.

Exam tip

Key terms

• Antagonistic muscles, a pair of muscles producing opposite movements across a joint.
• Tendon, a tough band connecting a muscle to a bone.
• Ligament, a tough band connecting one bone to another at a joint.
• Exoskeleton, a hard external skeleton found in some other animals, unlike the human internal skeleton.

Source:SRC-DSKP-EN

Frequently asked questions

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