Skeletal Muscle Physio II Flashcards
What is an Isotonic contraction?
Muscle changes length, keeping a constant tension
Can be concentric or eccentric
What is a concentric contraction?
Muscle decreases length against opposing load, i.e. lifting weight up
What is an eccentric contraction?
Muscle increases in length as it resists load, i.e. pushing something down
What is an isometric contraction?
Muscle does not shorten and tension builds up
What is the amount of active tension generated dependent on and why?
Muscle length
Depends on the number of crossbridges that are able to form
Too long - too little cross bridges
Too short - actin filaments push on each other, distorting the filaments and weakening cross bridges
What is the optimal length?
The length of muscle where maximum force is generated
What is passive tension?
Tension generated by the structure of the muscle fiber itself, caused by resistance of muscle’s elasticity to stretch
Also called preload
What is total tension?
Sum of active and passive tension
Generated when muscle is stimulated to contract at different preloads
What is active tension?
Generated by the contractile process
What is the force-velocity relationship?
As you increase the load, the velocity decreases
Velocity is determined by the active tension generated
What are type I fibers?
Slow-twitch, slow myosin ATPase
Loaded with mitochondria - use ox phos
Rich in myoglobin
Resistant to fatigue
What are type IIa fibers?
Fast-twitch, fast myosin ATPase
Loaded with mitochondria
Use ox phos and glycolysis
Rich in myoglobin
moderately fatigue-resistant
What are type IIb fibers?
Fast-twitch, fast myosin ATPase
Rich in glycogen
Depend on glycolysis
Fatigue easily
Low in myoglobin
What is a motor unit?
Group of muscle fibers innervated by the same motor neuron
What is the innervation ratio?
Number of fibers innervated by a motor unit
What is a Type I motor unit?
Innervate Type I muscle fibers
Few muscle fibers innervate - small IR
Slower-conducting
Fine, graded movements
What is a Type II motor unit?
Innervate Type II muscle fibers
More muscle fibers innervate - large innervation ratie
Faster-conducting
Coarse movments
What are two ways that the tension of the entire muscle can be increased via motor units?
Recruitment- increasing number of motor units (Slow
–> fast)
Summation - increasing frequency of individual motor unit firing
What is fatigue?
Decline in the ability of muscle to generate force
Glycogen and creatine phosphate stores depleted
ATP levels do not decrease substantially
What factors could cause fatigue?
Decreased motor neuron firing
Decreased oxygen
Impaired Ca release from sarcoplasmic reticulum
What happens to motor units in aging?
Decrease in total number
Increase in number of fibers/motor unit
What occurs to muscles with aging?
Atrophy - decrease in muscle mass
Decrease in max force and power of contraction
Decrease in total number of fibers
Decrease in number of mitochondria
What is sarcopenia?
Decrease in muscle mass and strength
Fewer satellite cells
Describe muscular dystrophy.
Progressive skeletal muscle weakness, defects in muscle proteins, and death of muscle cells and tissue
Major forms are Duchenne and Becker’s
Both involve defects in dystrophin
How does a defect in dystrophin cause muscular dystrophy?
Lead to instability of the sarcolemma which leads to damage of muscle during contractions
Describe myopathy
Primary symptoms muscle weakness, but cramps, stiffness, and spasms can occur
Causes: congenital, genetic abnormalities in mitochondria, mutations in glucose metabolizing genes
Prognosis varies
What is Cachexia?
“Wasting Syndrome”
Loss of weight, muscle atrophy, fatigue, weakness and loss of appetite
Seen in patients with chronic diseases
Similar to sarcopenia
What is myostits?
Inflammation of the muscles
Results in muscle weakness and pain, particularly in trunk
Caused by injury, infection or autoimmune disease
What is Rhabdomyolysis?
Breakdown of muscle fibers resulting in the release of muscle fiber contents, particularly myoglobin, into the circulation
Can cause kidney damage (muscle contents release)
Most common causes are crush injury, overexertion, alcohol abuse, statins, and toxins
What is Malignant hyperthermia?
Defects in RYR1 channel that causes it to channel to open more easily and close more slowly
Activated by certain anesthetics and muscle relaxers
Leads to uncontrolled release of Ca
Muscles contract abnormally, leading to rigidity and heat production
