This section outlines common physiological issues affecting muscle function, including fatigue, cramps, and tetany, and explores related physiological concepts like rigor mortis.
Definition: A physiological state where muscles lose their ability to contract.
Causes:
Definition: A sustained, involuntary, and painful tetanic contraction of an entire muscle.
Characteristics:
Common Locations: Thigh and hip muscles.
Triggers:
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:
| 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 |
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.
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: