The foot is a perfect marriage of form and function. The foot contains 26 bones, 33 joints, 19 muscles and 107 ligaments.
The Musculoskeletal System
The skeletal system consists of bone, which is the hard substance that forms the framework of the body. Ligaments tie the bones together to form joints. Each bone and each joint has a name. The bone of the thigh is called the femur, the bones of the leg are called the tibia and fibula, and the joint between these bones is called the knee joint. The skeleton and all its parts are moved by muscles and tendons. Bones, ligaments, muscles, and tendons are the tissues of the locomotor or musculoskeletal system of the body.
Bones consist of two kinds of tissue
- Compact Tissue: the hard, outside part of a bone
- Cancellous Tissue: the spongy part on the inside
Bones are covered with fibrous membrane called periosteum. The periosteum contains nerve fibres and transmits pain sensation if inflamed or torn away from the underlying bone. The muscular system consists of muscle, which is the tough, elastic tissue that makes body parts move. The human body has more than 600 major muscles. Skeletal muscles hold the bones of the skeleton together and make the body move. Skeletal muscles vary greatly in size, depending on their function. For example, eye muscles are small and fairly weak, but thigh muscles are large and strong.
The ends of most skeletal muscles are attached to bones by a tough, flexible connective tissue called tendon. The origin of the muscle is the proximal end that is attached to bone that does not move when the muscle contracts (draws together). The distal end, the insertion, is attached to a bone that moves when the muscle contracts.
Skeletal muscles act in pairs called flexors and extensors.
- Flexor: bends a joint and decreases joint angle
- Extensor: does the opposite, and moves a limb away from the body
For example, the hamstring muscle at the back of the femur is a knee flexor. When it contracts, the knee bends and the leg moves toward the hip. The quadriceps muscle at the front of the femur is an extensor. When it contracts, the knee straightens and the leg moves away from the hip. At the same time, the hamstring relaxes so the quadriceps can pull the limb back to its original length.
Joints and Ligaments
A joint is the place that two or more bones meet. This is also called an articulation. Freely mobile joints such as the elbow and knee contain a synovial cavity. This cavity is lined inside by synovial membrane, which produces joint fluid (“synovial fluid”). The fluid reduces the friction of the moving bones. The synovial membrane is surrounded by a fibrous joint capsule which, in key places, is reinforced by ligaments.
Joints are protected from wear and tear in several ways. A smooth layer of cartilage (gristle) covers the end of bones that move over one another. The elasticity of cartilage breaks the force of sudden shocks and also, the smooth quality of the cartilage makes a joint move easily. In addition to cartilage, the synovial fluid keeps the joints moist and lubricated. Bones are held together at the joint by strong ligaments that attach above and below the joint. The “joint capsule” encircles the joint and seals it to maintain the synovial fluid inside the capsule. This creates the “synovial cavity” (see diagram).
A ligament is a fibrous tissue that holds organs of the body in place and fastens bones together. Ligaments are grouped together in cords, bands, or sheets. A sprain occurs when ligaments covering a joint are torn and twisted. A sprained ankle is a partial tearing of the talofibular ligament that binds the bones of the lower leg to the bones of the foot. Ligament heal slowly and they may not fully heal if they are completely torn apart. Fascia is broad connective tissue band serving a stabilization and supportive function (e.g. iliotibial band, plantar fascia).