Muscle V

Question 1

Why does small stimulus not not cause AP in larger diameter motor neuron

Answer 1

• longer distance, more resistance (cytoplasmic resistance)
• more leakage
• more decay

Question 2

What is the size principle

Answer 2

Size of motor neuron determines type of muscle fibre that exists within motor unit
Small diameter= small diameter muscle fibers

Question 3

What do smaller motor neurons innervate

Answer 3

Least number of (small diameter) muscle fibers (slow-oxidative) constituting small motor units

Question 4

What do intermediate size motor neurons tend to innervate

Answer 4

Intermediate number (medium diameter) muscle fibers (fast-oxidative-glycolytic) establishing intermediate sized motor units

Question 5

What do large motor neurons tend to innervate

Answer 5

A large number of (large diameter) muscle fibers (fast-glycolytic) making up large motor units

Question 6

What is asynchronous recruitment

Answer 6

During submaximal contraction the CNS modulates firing rates of upper motor neurons to allow different motor units to maintain contraction and prevent fatigue

Question 7

What is tension

Answer 7

Force tending to pull the attachment points of a muscle toward one another (skeletal muscle)

Question 8

What is an isotonic contraction

Answer 8

Muscle contracts, shortens, creates enough force to move load

Question 9

What is isometric contraction

Answer 9

Muscle contracts but does not shorten. Force created cannot move load

Question 10

What are two types of isotonic contractions

Answer 10

Concentric: muscle shortens while generating force
Eccentric: muscle lengthens while generating force

Question 11

How do sarcomeres shorten during isometric contraction without muscle changing length?

Answer 11

• elastic elements in tendons, elastic and connective tissue in and around muscle fibres
• every contraction begins with isometric one
• stretch first allowing for shorten

Question 12

What are 3 skeletal muscle adaptations?

Answer 12

1. Hypertrophy/atrophy
2. Increase in ATP synthesizing capacity
3. Neural adaptations

Question 13

How do you increase ATP synthesizing capacity

Answer 13

Increase in mitochondria size and number
Increased capillary density
Increase in glycolytic enzyme

Question 14

What are neural adaptations involved in muscle adaptation?

Answer 14

Increased ability to recruit motor units
Reduced inhibitory input from golgi tendon organs

Question 15

How is muscle mass remodeled?

Answer 15

Changing rates of contractile protein synthesis and degradation

Question 16

What causes changing rates of protein sysnthesis and degradation

Answer 16

Regulated by pathways that are influenced by mechanical stress, physical activity, availability of nutrients, growth factors and age

Question 17

How do we increase muscle mass

Answer 17

Protein sysnthesis>protein degradation

Question 18

What are the two proposed mechanisms of increasing muscle mass

Answer 18

Hypertrophy (increase diameter) and hyperplasia (increase number)

Question 19

What do myosatellite cells do in humans

Answer 19

Muscle repair

Question 20

How do satellite cells respond to an injury

Answer 20

1. Become activated and proliferate
2. Migrate to damaged region
3. Depend on severity, fuse to muscle fiber to cause regeneration

Question 21

What is muscle hypertrophy

Answer 21

Increase in size of sarcomeres and number of contractile proteins (myosin + actin)
Increased myofibrils
Increased Sarcoplasmic storage (glycogen)

Question 22

What type of fiber shows greater rate of hypertrophy

Answer 22

Type II
- ratio is genetically predetermined

Question 23

What is skeletal muscle atrophy

Answer 23

Protein degradation>protein synthesis
Reduction in cross sectional area of entire muscle, and decrease in myofibrillar proteins

Question 24

Why does atrophy happen

Answer 24

Immobilization
Bed rest
Unloading (astronauts)
Food deprivation
Age (sarcopenia)