Glossary 2 A Arthritis Arthritis occurs when the smooth cartilage surface lining the bone ends, in the the joints is worn away. This can be caused by wear (osteoarthritis) or inflammatory conditions (Rheumatoid arthritis). B Brachial Plexus The brachial plexus refers to the network of nerves which originate from the spinal cord in your neck which pass into the arm, thereafter controlling all muscle and sensory functions of the hand and arm.