Muscle Damage & Repair

Split into two phases: degeneration (necrosis and inflammation) and regeneration (activation and differentiation of satellite cells, myofibre repair and formation).

Degeneration

• Necrosis- digestion of damage
• Damage to sarcolemma makes cell ‘leaky’ – often see Creatine Kinase in plasma
• Protease enzymes digest damaged tissue (autolysis)
• Inflammatory cell infiltration
• Neutrophils (primary phagocytes) within 1-6 hours of damage
• Macrophages invade and become predominant
• Phagocytose cell fragments

Regeneration

• Satellite cells
• Mononuclear cells located between the base membrane and sarcolemma
• Resemble nuclei but are actually unfused myoblasts
• Population declines with age
• Satellite cells align along base membrane with the help of the lengthening and shortening of the cells
• The formation of muscle fibres initiates generation of contractile proteins (actin and myosin)

Inflammation is the increased movement of plasma and leukocytes (especially granulocytes) from the blood into the injured tissues. A series of biological events then propagate and mature the inflammatory response.