Lecture 12: Muscle 6 Flashcards
Fatigue
the decreased capacity of a muscle to do work and its reduced efficiently of performance that normally follows a period of activity
Three main types of fatigue
- Muscle
- Neuromuscular
- Central
Muscle fatigue
Occurs when exercising muscle can no longer respond to stimulation with the same degree of contractile activity
Two possible causes of muscle fatigue
- Accumulation of lactic acid
- Depletion of energy stores
Accumulation of lactic acid may inhibit
key enzymes in the energy-producing pathways or excitation-contraction process
Depletion of energy stores
ATP is not present in sufficient amounts
Muscle fatiguw time of onset varies with
- Type of muscle fiber
- Intensity of muscle activity
Where does neuromuscular fatigue occur
neuromuscular junction
Neuromuscular fatigue
- Also called synaptic fatigue
- Active motor neurons are not able to synthesize Ach rapidly enough to sustain chemical transmission of action potentials from motor neurons to muscle
What type of fatigue is rare under normal conditions?
neuromuscular fatigue
Central fatigue
-Occurs when CNS no longer adequately activates the motor neurons supplying the working muscle
Also known as psychological fatigue
What three things happen during intense muscular activity
- Blood vessels in muscles dilate
- Blood flow increase
- Oxygen delivery increase
When muscular exertion is very great, oxygen cant be supplied to muscles fast enough which means
cellular respiration cant produce enough atp. It starts to get derived from non-oxidative sources such as anaerobic glycolysis
Oxygen debt
Recovery period where after intense muscular activity has stopped, the rate of breathing accelerates and continues for a period of time and O2 consumption is above resting level
Extra O2 is used to restore metabolic conditions to the resting level
The extra O2 in oxygen debt is used to (3)
- Convert lactic acid to pyruvic acid then to glucose in the liver. Glucose is used to help restore glycogen levels in muscle fibers and liver. Pyruvic acid is used for ATP production
- Resynthesize creatine phosphate
- Replace the O2 removed from myoglobin
Three steps in contraction-relaxation process the require ATP
- Splitting of ATP by myosin ATPase provides the energy for the power stroke of the cross-bridge
- Binding (but not splitting) of a fresh molecules of ATP t myosin permits detachment of bridge from the actin filament at the end of a power stroke so that the cycle can be repeated. This ATP is subsequently split to provide energy for the next stroke of the cross bridge
- Active transport of Ca back into the SR
Three sources of ATP
- Creatine phosphate
- Oxidative phosphorylation
- Glycolysis
Creatine phosphate
- First energy storehouse tapped at the onset of contractile activity
- Supports short bursts of high-intensity contractile effort such as sprints
Where does oxidative phosphorylation take place
in mitochondria, if sufficient O2 is present
ATP yield of oxidative phosphorylation
36 per glucose molecule
O2 required by oxidative phosphorylation is delivered by
the blood
Increased O2 is made available by (4)
- Deeper, more rapid breathing
- Heart contracts more rapidly and forcefully
- Dilated of blood vessels supplying active muscle
- In some muscle fibers (red), there is an abundance of myoglobin which stores O2 and increases the rate of O2 transfer from blood into muscle fibers
Glycolysis ATP yield
2 per glucose
Does glycolysis require O2?
no
Glycolysis is associated with
Lactic acid production - fall in muscle pH - muscle fatigue
Skeletal muscle varies in color depending on
the content of myoglobin (red)
Skeletal muscle fibers with high myoglobin vs low
red muscle fibers vs white mf
Red muscle fibers have more
mitochondria and blood capillaries
Skeletal muscle fibers contract and relax with different
velocites
Whether a fiber is slow twitch or fast depends on
how rapidly it splits ATP
