Part 3: Muscle Growth and Repair Flashcards
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?
- Slow twitch fibers are first initiated and begin to contract.
- Fast twitch muscles type 2a and 2b recruited.
- Type 2b muscles contract and max out quickly.
- Type 2a contract and max out relatively quickly.
- 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:
- Golgie tendon organs (GTOs)
- 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:
- GTOs detect muscle tension in the tendons.
- GTOs relay the amount of tension in a muscle via type 1b afferent neurons.
- 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.
- CNS sends its response to the muscle via alpha motor neurons.
- GTOs send information to the CNS regarding muscle tension via _______.
- 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:
- onset of contraction
- Type 1A fibers sense change
- Bag fibers slacken
- gamma motor neurons fire to increase tension and reactivate Type 1A fibers
- Continued contraction
- 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:
- Secrete myokines
-
Grow:
- Hypertrophy
- Hyperplasia
-
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
Lower intensity endurance training results in an increase in:
- an increase in type 1 muscle fiber:
- oxidative capacity
- mitochondria
- capillary density
Physical training at high levels of resistance will result in:
- hypertrophy of type 2 muscle fibers (fast-twitch) with a modest effect on the aerobic (oxidative) capacity of these fibers.
Two anabolic androgenic steroids:
- testosterone and dihydrotestosterone
- effects mediated through the activation of the androgen receptor
What occurs when anabolic androgenic steroids bind to androgen receptors?
- anabolic (proteogenic) effects
- anti-catabolic (competitive binding to glucocorticoid receptor) effects
Anabolic (proteogenic) effects of testosterone and dihydrotestosterone binding to androgen receptors:
- Stimulation of:
- satellite cell proliferation
- growth hormone (GH) secretion
- insulin-like growth factor-1 (IGF-1) expression
Growth hormone (GH) secretion site and function:
- secreted from somatotropes (anterior pituitary)
- induces positive nitrogen balance and proteogenesis
- stimulates hepatic IGF-1 production
Insulin-like growth factor-1 (IGF-1) secretion site and function:
- ubiquitously expressed in skeletal muscle
- stimulates proteogenesis
- stimulates regeneration (induces satellite cell mitosis)
