Part 3: Muscle Growth and Repair Flashcards Preview

SF1.12 Muscle Physiology (ZACHOW) > Part 3: Muscle Growth and Repair > Flashcards

Flashcards in Part 3: Muscle Growth and Repair Deck (37)
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The three types of muscle:

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


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

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


Type 1 Muscle:

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


Type 2a Muscle:

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


Type 2b Muscle:

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


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

What is the order?

  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.


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

  • The isometric to isotonic transition.


Eccentric phase of muscle contraction is:

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


Concentric phase of muscle contraction is:

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


The two types of muscle stress sensors:

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


Golgi tendon organs (GTO):

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


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

  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.


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

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


Muscle spindles monitor:

  • 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.


Muscles fibers consist of:

extrafusal and intrafusal fibers


Muscle spindles are located in:

  • intrafusal fibers of muscle fibers


Muscle spindles (intrafusal fibers) contain:

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


Role of type 1a afferent neurons in muscle spindles: 

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


Role of type 2 afferent neurons in muscle spindles: 

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


Role of gamma motor neurons in muscle spindles: 

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


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

  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


Muscle hypertrophy: 

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


Muscle hyperplasia: 

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


In response to sufficient work, muscle will:

  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


Satellite cells in muscle become active when?

  • 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 


Myostatin (GDF-9):

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


Process of muscle repair following work:

  • 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


Myokines have what kinds of functions?

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


Myokines stimulate:

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


Myokines negatively influence:

  • neurodegeneration