Chapter 10: Types of Muscle Contractions and Fibers
Hypertrophy
increase in the diameter of muscle fibers from forceful repetitive muscular activity such as weightlifting
Hypertonia
increased muscle tone; muscles are stiff or rigid
Regeneration of Smooth Muscle
limited capacity for division and regeneration
Isotonic Muscle Contraction
muscle contracts and shortens, and bones MOVE 2 Types: 1. Concentric 2. Eccentric
Isometric Muscle Contraction
muscle contracts but does not shorten, and bones do NOT move
Atrophy
wasting away of muscles due to disuse or severing the nerve supply
Fast Fibers
- F.G. = Fast Glycolytic Skeletal Muscle - WHITE muscle fiber - largest diameter = STRONGEST - fast contraction rate - low fatigue resistance - few mitochondria - Location = arm muscles
Intermediate Fibers
- F.O.G. = Fast Oxidative Glycolytic Skeletal Muscle - WHITE muscle fiber, myoglobin content - mid-sized fiber diameter - fast contraction rate - intermediate fatigue resistance - intermediate number of mitochondria - Location = leg muscles (running/walking)
Slow Fibers
- S.O. = Slow Oxidative Skeletal Muscle - RED muscle fiber (high in Myoglobin content and has many mitochondria) - smallest diameter so least powerful - slow contraction rate - high fatigue resistance - Location: neck muscles, back, and calf muscles
Skeletal Muscle Fiber Types
- a skeletal muscle fiber is either "slow" or "fast" depending on how fast ATP is hydrolyzed in the myosin heads 3 Types 1. Slow Fibers 2. Intermediate Fibers 3. Fast Fibers
Complete Tetanus
- a sustained muscle contraction with NO relaxation between stimuli - muscle is stimulated 80-100 times per second - monogram goes straight up with no stair steps, levels off, and then drops back down when the muscle fatigues
Incomplete Tetanus
- a sustained muscle contraction with partial relaxation between stimuli - muscle is stimulated 20-30 times per second; shows a stair step effect, with each of the first few contractions being a little stronger than the last
Twitch
- brief contraction of ALL muscle fibers in a motor unit in response to a single action potential - during latent period on myogram, the sarcolemma is depolarized and repolarized by the stimulus (action potential) and the SR releases calcium ions, which bind to Troponin allowing contraction phase
Regeneration of Skeletal Muscle
- cannot divide - limited power of regeneration - occasional new cells may be derived from satellite cells
Wave Summation
- increased strength of a contraction resulting from the application of a second stimulus BEFORE the muscle has completely relaxed after a previous stimulus - stair step increase in strength of contraction
Treppe
- increased strength of contraction resulting from the application of a second stimulus AFTER the muscle has completely relaxed subsequent to a previous stimulus - between 10-20 stimuli per second will produce a myogram showing the stair step phenomenon of treppe
Muscle Tone
- maintained due to partial contraction of relaxed portions of skeletal muscles - there are ALWAYS a few muscle fibers within a muscle that are contracted while most are relaxed - this is ESSENTIAL in maintaining posture
Muscles and Aging
- starting at age 30, there is progressive loss of skeletal muscle, which is replaced by fat - muscle reflexes slow, and the strength of muscle decreases
Types of Muscle Contraction
1. Isotonic 2. Isometric
Types of Muscle Contraction based on Stimuli
1. Twitch 2. Wave Summation 3. Treppe 4. Tetanus (Incomplete and Complete)
Regeneration of Cardiac Muscle
cannot divide or regenerate
Hypotonia
decreased or lost muscle tone; muscles are "flaccid"
Concentric (Type of Isotonic)
muscles SHORTEN, bones move, and angle at joint decreases (FLEXION)
Eccentric (Type of Isotonic)
overall length of muscle INCREASES during a muscle contraction, and the angle at joint increases (EXTENSION)
Recruitment
process of INCREASING the number of ACTIVE MOTOR UNITS, which prevents fatigue and provides even muscle contraction rather than a series of jerky movements