Which of the following is a primary function of the skin's sebaceous glands?

A. Fibromyalgia:Fibromyalgia is a chronic pain syndrome characterized by widespread musculoskeletal pain and fatigue, not a primary disorder of the neuromuscular junction.
B. Muscular dystrophy:Muscular dystrophy represents genetic disorders causing progressive muscle fiber degeneration rather than a problem at the neuromuscular junction.
C. Polymyositis:Polymyositis is an inflammatory myopathy causing proximal muscle weakness due to muscle inflammation, not a junctional transmission defect.
D. Myasthenia gravis:Myasthenia gravis is an autoimmune disorder that impairs acetylcholine receptor function at the neuromuscular junction, producing fluctuating muscle weakness and fatigability.

A. Normal joint function:Crepitus is not typically a sign of a normally functioning joint and usually indicates an underlying change in joint surfaces.
B. Inflammation of the synovial membrane:Synovial inflammation (synovitis) can cause pain and swelling but crepitus more specifically implies mechanical roughness rather than inflammation alone.
C. Presence of air in the joint space:Air in a joint (pneumarthrosis) is uncommon and would not be the usual explanation for the grinding or crackling sensation felt as crepitus.
D. Degeneration of joint structures:Crepitus often reflects irregular or roughened articular surfaces from wear or degeneration (for example osteoarthritis) producing a grating sensation during movement.