Muscle V Flashcards
Why does small stimulus not not cause AP in larger diameter motor neuron
- longer distance, more resistance (cytoplasmic resistance)
- more leakage
- more decay
What is the size principle
Size of motor neuron determines type of muscle fibre that exists within motor unit
Small diameter= small diameter muscle fibers
What do smaller motor neurons innervate
Least number of (small diameter) muscle fibers (slow-oxidative) constituting small motor units
What do intermediate size motor neurons tend to innervate
Intermediate number (medium diameter) muscle fibers (fast-oxidative-glycolytic) establishing intermediate sized motor units
What do large motor neurons tend to innervate
A large number of (large diameter) muscle fibers (fast-glycolytic) making up large motor units
What is asynchronous recruitment
During submaximal contraction the CNS modulates firing rates of upper motor neurons to allow different motor units to maintain contraction and prevent fatigue
What is tension
Force tending to pull the attachment points of a muscle toward one another (skeletal muscle)
What is an isotonic contraction
Muscle contracts, shortens, creates enough force to move load
What is isometric contraction
Muscle contracts but does not shorten. Force created cannot move load
What are two types of isotonic contractions
Concentric: muscle shortens while generating force
Eccentric: muscle lengthens while generating force
How do sarcomeres shorten during isometric contraction without muscle changing length?
- elastic elements in tendons, elastic and connective tissue in and around muscle fibres
- every contraction begins with isometric one
- stretch first allowing for shorten
What are 3 skeletal muscle adaptations?
- Hypertrophy/atrophy
- Increase in ATP synthesizing capacity
- Neural adaptations
How do you increase ATP synthesizing capacity
Increase in mitochondria size and number
Increased capillary density
Increase in glycolytic enzyme
What are neural adaptations involved in muscle adaptation?
Increased ability to recruit motor units
Reduced inhibitory input from golgi tendon organs
How is muscle mass remodeled?
Changing rates of contractile protein synthesis and degradation
What causes changing rates of protein sysnthesis and degradation
Regulated by pathways that are influenced by mechanical stress, physical activity, availability of nutrients, growth factors and age
How do we increase muscle mass
Protein sysnthesis>protein degradation
What are the two proposed mechanisms of increasing muscle mass
Hypertrophy (increase diameter) and hyperplasia (increase number)
What do myosatellite cells do in humans
Muscle repair
How do satellite cells respond to an injury
- Become activated and proliferate
- Migrate to damaged region
- Depend on severity, fuse to muscle fiber to cause regeneration
What is muscle hypertrophy
Increase in size of sarcomeres and number of contractile proteins (myosin + actin)
Increased myofibrils
Increased Sarcoplasmic storage (glycogen)
What type of fiber shows greater rate of hypertrophy
Type II
- ratio is genetically predetermined
What is skeletal muscle atrophy
Protein degradation>protein synthesis
Reduction in cross sectional area of entire muscle, and decrease in myofibrillar proteins
Why does atrophy happen
Immobilization
Bed rest
Unloading (astronauts)
Food deprivation
Age (sarcopenia)
