Muscle Part 3 Flashcards
The speed of contraction of slow or fast fibers is determined by
The speed at which myosin ATPases split ATP
Metabolic pathways for ATP synthesis
- Oxidative fibers—use aerobic pathways
- Glycolytic fibers—use anaerobic glycolysis
What is the first source of energy used in the muscle?
Glycolysis
What are the three types of muscle fibers?
- Slow oxidative fibers, type 1 (small in diameter)
- Fast oxidative-glycolytic fibers type 2A (Intermediate in diameter)
- Fast glycolytic fibers type 2X (large in diameter)
Slow Oxidative Fibers, type 1
-Primary source of ATP: Oxidative phosphorylation
-Many mitochondria
-Small diameter
-High myoglobin content
-Slow contraction velocity and rate of fatigue
-Low Myosin-ATPase activity
Fast Oxidative-Glycolytic Fibers, type 2
-Oxidative phosphorylation
-High myoglobin content
Fast Glycolytic Fibers
-Gylcolysis
-Few mitochondria
-Low myoglobin content
-High glycolytic enzyme activity
-High myosin ATP-ase activity
Is weight lifting fast or slow twitch?
Fast twitch
Muscle Tone
Constant, slightly contracted state of all muscles
1) Due to spinal reflexes
2) Groups of motor units alternately activated in response to input from stretch receptors in muscles
Subthreshold stimuli
Threshold stimulus
Maximal stimulus
no observable contractions, only graded potential, not enough to open Na+ gated potential to generate an AP
stimulus strength causing first observable muscle contraction
strongest stimulus that increases contractile force
Recruitment works on size principle
Motor units with smallest (in diameter) muscle fibers recruited first
Beyond maximal stimulus
no increase in force of
contraction
Force of contraction depends on
number of cross bridges attached
Affected by:
1) Number of muscle fibers stimulated
2) Relative size of fibers– hypertrophy of cells increases strength
3) Frequency of stimulation
4) Degree of muscle stretch
Shortening velocity of a whole muscle depends upon
- Load
- Motor unit type (slow or fast twitch)
- Number of motor units recruited
Disuse atrophy
– Result of immobilization
– Muscle strength declines 5% per day
Denervation atrophy
– Without neural stimulation muscles atrophy to 25% initial size
– Fibrous connective tissue replaces lost muscle tissue= rehabilitation impossible
Adaptations to Exercise: Low-Intensity Exercise
Endurance (aerobic) exercise such as distance running
Slow-twitch fibers recruited
– Leads to increased
* Muscle capillaries
* Number of mitochondria
* Myoglobin synthesis
– May convert fast glycolytic fibers into fast oxidative fibers
– Results in greater endurance, strength, and resistance to fatigue
Adaptations to Exercise: High-Intensity Exercise
Resistance exercise (anaerobic) such as weight lifting
Fast-twitch fibers recruited
* results in
– Muscle hypertrophy
* Due primarily to increase in fiber size
* More myofibrils= more x-bridges= more strength
* More glycolytic activity
– May convert fast oxidative fibers (Type 2A) into fast glycolytic fibers(Type 2X)
– Results in powerful muscles but with little capacity for endurance and fatigue rapidly
Motor endplate disease
Also known as NMJ disease.
The neuromuscular junction (NMJ) is the chemical synapse where motor neurons and muscle fibers meet. Motor endplates (MEPs) are specialized structures within the NMJ that receive electrical signals from motor neurons and trigger muscle contractions. Motor endplate disease (MED) is a condition that impairs the maturation of the neuromuscular junction.
Includes botulism and myasthenia graves- Destruction of nicotinic Ach-receptor proteins of the motor
end plate
Myopathy
Affects the muscle itself.
Includes Duchenne muscular dystrophy.
Neurological disorder
Affects the nerves.
Can result from damage to the myelin sheath.
Includes ALS.
Muscular Dystrophy
Affects one in every 3,500 males (fewer females)
* Absence or defect in costameres in striated muscle
– Costameres link the Z-disks of the outermost myofibrils to the sarcolemma and extracellular matrix.
* Progressive degeneration of skeletal and cardiac muscle fibers
* Death from respiratory or cardiac failure
Hypocalcemic Tetany
Involuntary tetanic contraction
Low extracellular Ca2+ hypocalcemia)= less +++ charge
in the ECF= more Na+ channels open in sarcolemma= depolarization= spontaneous action potentials
