Comparison of the Microscopic Structure of Compact Bone - Assignment Example

Spongy bones are found on the heads of the long bones such as femur, humerus, radius, tibia, and fibula, and in between flat bones such as the skull, while the compact bone forms the external surface of all bones (Saladin 172). Anatomically, joints are connections between distinct joints. They exist so the bones are interconnected, and can be one skeletal system. They can exponentially increase the range of movement of our extremities, just like our knee, elbow, shoulder and metacarpal joints, or they can strengthen the structure of our body, just like our pubic symphysis and skull sutures.

Hyaline cartilage and synovial fluid lubricate joints and make movement easier. Fibrocartilage makes the joints strong against compression and shock. The enlarged epiphysis of the bones it connects also provide strength (Saladin 172-173). Once the action potential reaches the motor nerve endings on muscle fibers, the nerve secretes acetylcholine, which initiates the influx of sodium ions into the muscle fiber, causing an action potential at the membrane. This potential travels along the muscle fiber membrane, and in the process depolarizing in the membrane.

This then causes the sarcoplasmic reticulum to release large quantities of calcium ions, which initiate the binding of actin and myosin filaments that occurs during the contraction. After muscle contraction, calcium ions are returned back into the sarcoplasmic reticulum, causing muscle relaxation (Guyton and Hall 74). Upon receiving an impulse from the musculocutaneous nerve (Saladin 362), the biceps brachii (Saladin 328), exerts effort on the radius, with resistance contributed by the weight of the forearm or anything held in hand.

Fulcrum is the elbow (Saladin 309).