## Muscle Disorders This section outlines common physiological issues affecting muscle function, including fatigue, cramps, and tetany, and explores related physiological concepts like rigor mortis. ## Muscle Fatigue **Definition**: A physiological state where muscles lose their ability to contract. **Causes**: * Accumulation of lactic acid, which lowers the muscle pH and causes an aching sensation. * Ionic imbalance within the muscle cells. --- ## Cramp **Definition**: A sustained, involuntary, and painful tetanic contraction of an entire muscle. **Characteristics**: * Lasts from a few seconds to several hours. * Causes the muscle to become taut (tightly drawn). **Common Locations**: Thigh and hip muscles. **Triggers**: * Often occurs at night or after strenuous exercise. * Can be a sign of low blood sugar, electrolyte depletion, dehydration, or irritability of spinal cord neurons. --- ## Tetany **Definition**: A condition characterized by continuous muscle contractions and convulsions due to electrolyte imbalance, specifically low calcium levels. **Mechanism**: Low calcium increases the excitability of neurons, leading to spontaneous muscle stimulation. **Symptoms**: * Body shakes from continuous muscle contractions. * Loss of sensation. * In severe, untreated cases: spasm of the larynx, paralysis, and death. --- ### Comparison: Tetany vs. Tetanus | Feature | Tetany | Tetanus | | :--- | :--- | :--- | | **Cause** | Electrolyte imbalance (e.g., low calcium) | Bacterial infection (*Clostridium tetani*) | | **Mechanism** | Overly stimulated peripheral nerves and muscles | Toxin from the bacteria blocks inhibitory nerve signals | | **Symptoms** | Muscle spasms, cramps, potential larynx spasms | Muscle stiffness and spasms, especially in the jaw ("lockjaw") | | **Treatment** | Address the underlying electrolyte imbalance | Tetanus immune globulin, antibiotics, and supportive care | --- ## Related Physiological Concepts ### Muscle Action: Pull vs. Push Muscles work by contracting, which causes them to shorten. This shortening action pulls on bones, which act as levers. Muscles cannot actively lengthen or push; they can only pull and then relax. Antagonistic muscle pairs are required to produce movement in opposite directions. For example, biceps pulls to bend the arm, triceps pulls to straighten it. --- ### Rigor Mortis **Definition**: The stiffening of joints and muscles of a body after death (literally "rigidity of death"). **Cause**: After death, ATP production ceases. ATP is required to detach the myosin heads from the actin filaments (break the cross-bridges) during muscle relaxation. **Mechanism**: Without ATP, the cross-bridges that were formed just before death remain locked, causing the muscles to become fixed in a state of partial contraction. **Timeline**: * Appears about 4 hours after death. * Lasts for approximately 34 hours. * Disappears as muscle proteins are broken down by cellular enzymes.