1. Bones and Joints
There are 206 bones in the adult body. Bones serve many functions, but basically they are points of attachments for muscles and ligaments. They also provide support for the body and protect the internal organs. In addition, they serve as storage reservoirs for minerals, including calcium and phosphate.
A joint is an articulation, or intersection, between two or more bones. Specific parts of joints are named after the bones which meet. For instance, the shoulder joint is actually three joints. The glenohumeral joint is where the arm meets the shoulder blade. The acromioclavicular (AC) joint is where the collarbone meets the shoulder blade. The scapulothoracic joint is where the shoulder blade meets the ribcage. This is usually not thought of as a joint, but it is! Any of the above areas can be a source of pain and disability. To further confuse matters, a shoulder dislocation involves the glenohumeral joint. However, a shoulder separation affects the AC joint.
2. Muscles
Muscle contractions cause motion across joints. Skeletal muscles are composed of muscle filaments that slide along each other in response to stimulation from a nerve. A "concentric" contraction refers to a muscle shortening as it contracts. When a muscle lengthens as it contracts, that is known as an "eccentric" contraction. Hence, technically we don't "flex" our biceps, we "contract" our biceps to bend or "flex" our elbows. Muscles can hypertrophy (grow bigger) or atrophy (grow smaller). There are two main types of skeletal muscle. Type I red muscle has lower strength, but higher aerobic capacity. It has higher endurance and is better for long-distance runners. Type II white muscle contracts more quickly with more power, but is anaerobic and has lower endurance. This is better for sprinters and power lifters.
3. Tendons and Ligaments
Tendons attach muscles to bones and allow a muscle contraction to move a bone or joint. The Achilles tendon attaches the calf muscles to the heel bone. When the calf muscles contract, the ankle plantarflexes. Ligaments attach bones to bones and provide stability to joints. The medial (MCL) and lateral (LCL) collateral ligaments of the knee connect the femur (thigh bone) and tibia (shin bone) on the sides of the joint. The anterior (ACL) and posterior (PCL) cruciate ligaments connect the femur and tibia and cross each other in the inside of the joint.
4. Strains and Sprains
A strain is partial tearing of a muscle, such as a hamstring strain. A sprain is partial tearing of a ligament, like an ankle sprain. These are usually accompanied by a popping or tearing sensation. There may be bruising and swelling from broken blood vessels. Strains and sprains are graded in severity from Grade 1 to Grade 3. These injuries are usually treated conservatively, without surgery. Remember RICE--rest, ice, compression and elevation. Anti-inflammatory medicines and physical therapy can also help you recover.
5. Nerves
Nerves innervate muscles and cause muscle contractions through electrochemical pathways. They also convey sensory information, such as touch and temperature, from the skin back to the brain. Nerves also play a role in proprioception, which is the awareness of where your body part is in relation to your surroundings. Full recovery from injury often requires proprioceptive rehabilitation. In fact, neuromuscular and proprioceptive training can prevent injuries as well. Injury to a nerve--ranging from a direct laceration to prolonged pressure--can cause numbness or muscle atrophy over time. Carpal tunnel syndrome of the wrist involves the median nerve and can cause numbness of the fingers or muscle wasting of the hand.
