Muscular System: Contraction Mechanics, Disorders, and Energy Sources

Comprehensive vocabulary flashcards covering neuromuscular junction disorders, length-tension properties, motor unit activation, twitch mechanics, stimulus frequency effects, isotonic vs. isometric contractions, and muscle energy systems.

Botulism

A form of food poisoning usually acquired from improperly canned foods in which the bacterium Clostridium botulinum blocks the release of ACh, inhibiting nerve transmission and causing muscle paralysis that can lead to death from respiratory failure.

Myasthenia gravis

A disease in which the body produces antibodies against acetylcholine (ACh) receptors, impairing nerve transmission and resulting in profound muscular weakness.

Tetanus ("lockjaw")

A disease caused by the bacterium Clostridium tetani that causes motor neurons to fire excessively, resulting in overstimulation, severe muscle spasms, and sustained contractions typically affecting jaw muscles first.

Curare

A poison once used on arrows and now used in anesthesia to relax skeletal muscles by binding to ACh receptor sites and blocking nerve transmission, causing paralysis that necessitates mechanical ventilation.

Length-tension relationship

The physiological principle stating that the strength of a muscle contraction depends directly upon the length of the fibers before contraction begins, with maximum tension occurring at an optimal resting length where thick and thin filaments partially overlap.

Muscle tone

A continuous state of partial contraction maintained by the nervous system stimulating fibers just enough to achieve optimal resting length, essential for maintaining posture and reacting quickly to balance disturbances.

Motor unit

A single motor neuron together with all of the individual muscle fibers it stimulates, which are scattered throughout the muscle to spread the force of contraction.

Threshold

The minimum electrical voltage or stimulus strength required to cause a muscle fiber to contract.

Twitch

A single, brief contraction and relaxation cycle that occurs when a muscle fiber receives an electrical stimulus at or above threshold.

Rigor mortis

A postmortem state of muscle rigidity resulting from the cessation of ATP production, which leaves myosin heads locked onto actin filaments; it peaks about $12\,\text{hours}$ after death and fades over the following $48\,\text{hours}$.

Slow-twitch (type I) fibers

Muscle fibers that respond slowly to stimuli, contain abundant mitochondria and a rich blood supply, utilize oxygen efficiently to produce ATP, and resist fatigue during long-duration endurance activities.

Fast-twitch (type II) fibers

Muscle fibers adapted for short bursts of speed or power that have fewer mitochondria and a poorer blood supply, but can absorb and release calcium rapidly to contract quickly, fatiguing faster than slow-twitch fibers.

Treppe

Also known as the staircase phenomenon; a condition where each successive muscle twitch is stronger than the previous one because the sarcoplasmic reticulum does not have sufficient time to fully reabsorb released calcium ions between rapid stimuli.

Incomplete tetanus

A condition of rapid muscle contractions with only partial relaxation between successive nerve impulses, causing subsequent contraction forces to build on prior ones.

Complete tetanus

A state of prolonged, sustained contraction that occurs when stimulation frequency is so high that the muscle fiber has no opportunity to relax between impulses.

Recruitment

The process of calling an increasing number of motor units into action as stimulus intensity increases, thereby generating a progressively stronger muscle contraction.

Isometric contraction

A type of contraction in which internal tension in the muscle increases while its overall length remains unchanged (meaning "same measurement").

Isotonic contraction

A type of contraction in which muscle tension remains constant while the muscle changes length to move a load (meaning "equal tension").

Creatine phosphate (CP)

A high-energy compound stored in muscle tissue that is broken down to rapidly regenerate waning ATP supplies at the onset of exercise, supplying fuel for about $20\,\text{seconds}$ of high-energy activity or $1\,\text{minute}$ of moderate activity.

Anaerobic fermentation

A metabolic pathway for glucose breakdown that operates without oxygen to rapidly generate ATP during intense bursts of activity, producing lactic acid as a byproduct.

Aerobic respiration

A metabolic process requiring oxygen that breaks down fatty acids at rest and glucose during sustained moderate activity (after about $10\,\text{minutes}$), generating large amounts of ATP along with non-toxic byproducts (carbon dioxide and water).

Oxygen debt

The extra oxygen consumed during heavy breathing following strenuous exercise to fuel the liver's conversion of accumulated lactic acid back into glucose.