Part 3: Muscle Growth and Repair

Question 1

The three types of muscle:

Answer 1

• Type 1 (slow twitch)
• Type 2A (fast twitch)
• Type 2B (fast twitch)

Question 2

Maximal generation of force following contraction for each muscle fiber type:

Answer 2

• Type 1: 100 msec
• Type 2a: 50 msec
• Type 2b: 25 msec

Question 3

Type 1 Muscle:

Answer 3

• Endurance
• Oxidative
• Well vascularized
• Small diameter
• “Slow twitch”

Question 4

Type 2a Muscle:

Answer 4

• Power and speed
• Some oxidative capacity
• “Fast twitch”

Question 5

Type 2b Muscle:

Answer 5

• Power and speed
• Anaerobic
• Less vascularized
• Large diameter
• “Fast twitch”

Question 6

When a muscle contracts, there will also be an orderly and sequential recruitment of motor units to accomplish this.

What is the order?

Answer 6

1. Slow twitch fibers are first initiated and begin to contract.
2. Fast twitch muscles type 2a and 2b recruited.
3. Type 2b muscles contract and max out quickly.
4. Type 2a contract and max out relatively quickly.
5. Type 1 fibers contract and max out over time.

Question 7

All contractions begin as isometric. What causes the displacement of load?

Answer 7

• The isometric to isotonic transition.

Question 8

Eccentric phase of muscle contraction is:

Answer 8

• Muscle lengthening to resist the force of gravity.
• Load is greater than the muscle force (afterload > preload).
  
  • e.g. downward movement of a squat

Question 9

Concentric phase of muscle contraction is:

Answer 9

• Muscle contraction/shortening.
• Muscle force greater than the load (preload > afterload).
  
  • e.g. upward movement of the squat.

Question 10

The two types of muscle stress sensors:

Answer 10

1. Golgie tendon organs (GTOs)
2. Muscle spindles

Question 11

Golgi tendon organs (GTO):

Answer 11

• located within tendons
• monitor the amount of tension a muscle is undergoing

Question 12

Process of Golgi tendon organs (GTO) stress information relay to the CNS:

Answer 12

1. GTOs detect muscle tension in the tendons.
2. GTOs relay the amount of tension in a muscle via type 1b afferent neurons.
3. CNS processes information and then either inhibits the lengthening of muscles or recruits ipsilateral muscles to slow the rate of muscle lengthening and decrease tension.
4. CNS sends its response to the muscle via alpha motor neurons.

Question 13

1. GTOs send information to the CNS regarding muscle tension via _______.
2. CNS responds to GTOs via ________.

Answer 13

• GTOs send via: type 1B afferent neurons
• CNS responds via: inhibitory or stimulatory interneurons linked to alpha motor neurons.

Question 14

Muscle spindles monitor:

Answer 14

• the change in length and the rate of change in length of muscles.
• determine the upper limit of how far a muscle can be contracted.
• muscle position in 3D space.

Question 15

Muscles fibers consist of:

Answer 15

extrafusal and intrafusal fibers

Question 16

Muscle spindles are located in:

Answer 16

• intrafusal fibers of muscle fibers

Question 17

Muscle spindles (intrafusal fibers) contain:

Answer 17

• bag fibers
• chain fibers
• type 1a afferent neurons
• type 2 afferent neurons
• gamma motor neurons

Question 18

Role of type 1a afferent neurons in muscle spindles:

Answer 18

• afferent fibers
• monitor length of the muscle and the changes in length.

Question 19

Role of type 2 afferent neurons in muscle spindles:

Answer 19

• afferent fibers
• monitor the static length of muscles.
• used in determining position in 3D space.

Question 20

Role of gamma motor neurons in muscle spindles:

Answer 20

• efferent fibers.
• increases the tension of the muscle spindle to reset type 1a fibers as sensors.

Question 21

Process of muscle spindle monitoring of muscle length and length rate of change:

Answer 21

1. onset of contraction
2. Type 1A fibers sense change
3. Bag fibers slacken
4. gamma motor neurons fire to increase tension and reactivate Type 1A fibers
5. Continued contraction
6. Type II fibers are slow adapting and provide constant monitoring

Question 22

Muscle hypertrophy:

Answer 22

• an increase in muscle fiber diameter
• the dominant form of muscle growth

Question 23

Muscle hyperplasia:

Answer 23

• an increase in the number of muscle fibers
• the lesser form of muscle growth

Question 24

In response to sufficient work, muscle will:

Answer 24

1. Secrete myokines
2. Grow:
   
   • Hypertrophy
   • Hyperplasia
3. Increase in:
   
   • microvasculature
   • mitochondrial enzyme content
   • the phosphagen system (i.e. creatine kinase)
   • glycogen stores
   • triglyceride stores

Question 25

Satellite cells in muscle become active when?

Answer 25

* via IGF-1 in response to work and injury * once active, they become myoblasts, accumulate onto muscle tears, and are the main source of muscle regeneration and growth

Question 26

Myostatin (GDF-9):

Answer 26

* blocks cell cycle progression within satellite cells * loss-of-function is associated with enhanced muscle mass in humans and some other mammalian species

Question 27

Process of muscle repair following work:

Answer 27

* **_initial response:_** * elevation in proteolytic genes, muscle injury broken down * **_hours later:_** * elevation in cytokines and supression of myostatin * satellite cells form myoblasts, accumulate on damaged muscle

Question 28

Myokines have what kinds of functions?

Answer 28

* Autocrine, paracrine, and/or endocrine functions * released in response to muscle work

Question 29

Myokines stimulate:

Answer 29

* lipolysis * gluconeogenesis * insulin secretion * osteogenesis * glucoregulatory proteins * anti-inflammatory

Question 30

Myokines negatively influence:

Answer 30

* neurodegeneration

Question 31

Lower intensity endurance training results in an increase in:

Answer 31

* an increase in type 1 muscle fiber: * oxidative capacity * mitochondria * capillary density

Question 32

Physical training at high levels of resistance will result in:

Answer 32

* hypertrophy of type 2 muscle fibers (fast-twitch) with a modest effect on the aerobic (oxidative) capacity of these fibers.

Question 33

Two anabolic androgenic steroids:

Answer 33

* testosterone and dihydrotestosterone * effects mediated through the activation of the androgen receptor

Question 34

What occurs when anabolic androgenic steroids bind to androgen receptors?

Answer 34

* anabolic (proteogenic) effects * anti-catabolic (competitive binding to glucocorticoid receptor) effects

Question 35

Anabolic (proteogenic) effects of testosterone and dihydrotestosterone binding to androgen receptors:

Answer 35

* Stimulation of: * satellite cell proliferation * growth hormone (GH) secretion * insulin-like growth factor-1 (IGF-1) expression

Question 36

Growth hormone (GH) secretion site and function:

Answer 36

* secreted from somatotropes (anterior pituitary) * induces positive nitrogen balance and proteogenesis * stimulates hepatic IGF-1 production

Question 37

Insulin-like growth factor-1 (IGF-1) secretion site and function:

Answer 37

* ubiquitously expressed in skeletal muscle * stimulates proteogenesis * stimulates regeneration (induces satellite cell mitosis)