Atrophy: Reduction of size, tone, and power of muscle, often caused by disuse.
Hypertrophy: Exercise-induced increase in muscle mass.
Disuse of a muscle can be caused by various factors.
Astronauts may suffer muscle atrophy due to the reduced gravitational force in space, leading to less muscle use.
Common Disorders & Ailments
Muscular Dystrophy: A collective term for several hereditary conditions in which skeletal muscles degenerate, lose strength, and are gradually replaced by fatty and fibrous tissue that impedes blood circulation, accelerating muscle degeneration in a fatal spiral of positive feedback.
Botulism: A potentially fatal muscular paralysis caused by a toxin produced by the bacterium Clostridium botulinum; the toxin prevents the release of acetylcholine, a muscle-stimulating compound, by muscle-related cells of the nervous system, leading to paralysis.
Cramps: Painful muscle spasms triggered by strenuous exercise, extreme cold, dehydration, salt (electrolyte) imbalance, low blood glucose, or reduced blood flow.
Contracture: Abnormal muscle shortening not caused by nerve stimulation; can result from the inability to remove calcium ions from the sarcoplasm or from the contraction of scar tissue (e.g., in people who have experienced severe burns).
Fibromyalgia: Chronic muscular pain and tenderness often associated with fatigue and sleep disturbances; can be caused by infectious diseases, physical or emotional trauma, or medications.
Crush Syndrome: A shock-like state following massive crushing of the muscles (e.g., in the aftermath of an earthquake, building collapse, or traffic accident); associated with high fever, heart irregularities caused by potassium ions released from the muscles, and kidney failure caused by blockage of the renal tubules with myoglobin released by the traumatized muscles.
Delayed Onset Muscle Soreness (DOMS): Pain, stiffness, and tenderness felt from several hours to a day after strenuous exercise; associated with trauma to the muscles, disruptions in the myofibrils and sarcolemma, and increased levels of myoglobin and muscle-fiber enzymes in the blood.
Myositis: Muscle inflammation and weakness resulting from infection or an autoimmune disease.
Myograms
Myograms measure the force of a muscle contraction in a skeletal muscle with time.
When a muscle is not allowed to relax completely between stimuli, the contraction gradually increases in intensity until it reaches a maximum (tetanus), which is sustained until the muscle fatigues.
Skeletal Muscle Fiber Types
Two main muscle fiber types:
Slow-twitch (Type I): Dark; contain myoglobin and have many surrounding capillaries.
Fast-twitch (Type II): Light; little or no myoglobin and fewer blood vessels.
Slow Twitch Fibres
Contract slowly but resist fatigue.
Produce most ATP aerobically, so tire only when the fuel supply is gone.
Glycogen and fat allow the abundant mitochondria to maintain steady, prolonged ATP production.
Best suited for endurance-type activities (e.g., biking, swimming, long-distance running).
Fast Twitch Fibres
Adapted for rapid generation of power but fatigue quickly.
Rich in glycogen; large number of sarcomeres.
Depend on anaerobic energy production, putting them at risk of lactate accumulation.
Best suited for short-term, power activities (e.g., sprinting, tennis, weight lifting).
Intermediate Fibres
Fast-twitch but high oxidative capacity (fatigues slowly).
The proportion can be increased by endurance training and genetics.
Force & Response Times
Skeletal muscles have different proportions of fast-twitch and slow-twitch fibers. Thus, the force and response times of their contractions differ.
Assignment
Read pages: 344 – 351
Lesson 3 – Check Your Understanding Questions
Quiz: Monday, January 16
Unit Final: Excretory System and Muscles – Tuesday, January 17