Common Muscle Disorders Flashcards
What do muscle fibers use for contraction?
Muscle fibers use ATP for contraction
How is ATP generated by the muscle cell?
ATP is generated by the muscle cell from:
- creatine phosphate
- glucose & glycogen
- fatty acids
What is direct phosphorylation?
The transfer of a phosphate group from creatine phosphate to ADP, which generates ATP.
What is oxidative metabolism?
The primary energy source for muscle through oxidative phosphorylation, which generates 34 ATP per glucose.
What is glycolytic metabolism?
The primary energy source for muscle through anaerobic glycolysis, which generates 2 ATP per glucose.
What happens if the muscle doesn’t have enough oxygen delivered to it by myoglobin?
If the effort is strong and sustained:
- the muscle might not have enough oxygen delivered to it by myoglobin
- resulting in anaerobic glycolysis
- with only 2 ATP formed per glucose and synthesis of lactic acid
What is the demand for ATP in a resting muscle fiber?
The demand for ATP is low in a resting muscle fiber
How is ATP generated in a resting muscle fiber?
By the breakdown of fatty acids in the mitochondria
What is the fate of glucose in a resting muscle fiber?
Some of the mitochondrial ATP is used to convert glucose to glycogen
What is creatine phosphate (CP)?
Creatine phosphate (CP) is a high-energy molecule that can be rapidly converted to ATP.
What is the role of mitochondria in a resting muscle fiber?
- generate ATP from the breakdown of fatty acids
- use some of this ATP to convert glucose to glycogen & creatine to creatine phosphate
- thus building up energy reserves in the muscle
What happens to the demand for ATP during moderate activity?
The demand for ATP increases
Is there still enough oxygen for the mitochondria to meet the increased demand during moderate activity?
Yes, there is still enough oxygen for the mitochondria to meet the increased demand
Is excess ATP produced during moderate activity?
No, there is no excess ATP produced during moderate activity
What is the primary source of ATP generation during moderate activity?
ATP is generated primarily by aerobic metabolism of glucose from stored glycogen
What happens if the glycogen reserves are low during moderate activity?
If the glycogen reserves are low, the muscle fiber can also break down other substrates, such as fatty acids.
What is all of the ATP being generated during moderate activity used for?
All of the ATP being generated is used to power muscle contraction.
What happens to the demand for ATP during peak activity?
The demand for ATP is enormous
Why can’t oxygen diffuse into the muscle fiber fast enough during peak activity?
Oxygen cannot diffuse into the fiber fast enough for the mitochondria to meet the enormous demand for ATP.
How much of the cell’s ATP needs can be met by the mitochondria during peak activity?
Only a third of the cell’s ATP needs can be met by the mitochondria during peak activity.
Where does the rest of the ATP come from during peak activity?
The rest of the ATP comes from glycolysis
What happens when pyruvate is produced faster than the mitochondria can utilize it during peak activity?
The pyruvate builds up in the cytosol
What happens to pyruvate in the cytosol during peak activity?
The pyruvate is converted to lactate
Why do hydrogen ions from ATP hydrolysis not get absorbed by the mitochondria during peak activity?
mitochondria is not able to keep up with the rate of H+ production
What is the consequence of the buildup of hydrogen ions during peak activity?
The buildup of hydrogen ions increases cytosol acidity, which inhibits muscle contraction, leading to rapid fatigue.
Question: What are slow fibers?
Muscle fibers that have:
- a smaller diameter
- appear darker due to myoglobin
- have lots of mitochondria; fatigue resistant
- extra capillaries
What are fast fibers?
Muscle fibers that have:
- a larger diameter
- appear paler in color; less myoglobin
- are easily fatigued due to fewer mitochondria and do more glycolysis
- fewer capillaries
What is muscle fatigue?
A decline in the ability of the muscle to sustain the strength of contraction.
What are the causes of muscle fatigue?
- rapid build-up of lactic acid
- decreased neurotransmitter at the synapse
- decrease in oxygen supply
- decrease in energy supply (glucose, glycogen, fatty-acids)
- psychological causes
How does exercise affect muscles?
Exercise increases:
- muscle size
- strength
- endurance
What is the effect of aerobic (endurance) exercise on muscles?
Aerobic exercise promotes increased oxidative capacity of the muscle fiber, resulting in:
- increased blood vessel supply
- increased mitochondria
- stronger, more flexible muscles with greater resistance to fatigue
What is the effect of resistance exercise (weight lifting) on muscles?
Resistance exercise increases glycolytic activity, which leads to:
- increased synthesis of glycolytic enzymes & myofibrils
- increased muscle size & strength
What hormones affect muscle growth?
- testosterone
- growth hormone (GH)
- insulin-like growth factor-1 (IGF-1)
- insulin
How does growth hormone (GH) affect muscle growth?
- produced by the pituitary gland
- stimulates the release of insulin-like growth factor 1 (IGF-1)
- which promotes muscle growth & increasing bone density
How does testosterone affect muscle growth?
Increases muscle mass and strength
What are ‘Double-Muscled’ animals?
Animals that have been selectively bred for increased muscle mass and a double-muscling phenotype
What is myostatin?
Myostatin is a protein that regulates muscle growth by inhibiting proliferation (cell growth)
What happens when myostatin is inhibited?
When myostatin is inhibited, muscle growth is increased
Why are some animals naturally double-muscled?
Because they have mutations that either reduce myostatin production or block its activity
What could cause muscle disorders?
Muscle disorders can be caused by:
- failures in signaling in the NS
- problems with synaptic transmission
- issues with the muscle itself
How are muscle cramps caused?
Muscle cramps are caused by hyperexcitability of the somatic motor neuron controlling the muscle
How can muscle cramps be relieved?
Stretching the muscle relieves muscle cramps by sending sensory information back to the CNS to inhibit the motor neurons
What are some consequences of muscle overuse and trauma?
Muscle overuse can result in muscle fatigue and trauma can cause tearing of the muscle tissue
What is muscle disuse?
Muscle disuse occurs when a muscle is not used or immobilized for an extended period
How can muscle disuse affect muscles?
Causes muscle atrophy
What is mucle atrophy?
Where the muscle fibers get smaller, and the blood supply to the muscle diminishes.
- muscle atrophy longer than a year is permanent
What are some examples of acquired muscle disorders?
Acquired disorders can result from:
- infectious diseases (e.g., influenza)
- poisoning by toxins (e.g., botulinum toxin)
- tetanus (e.g. tetanus toxin)
What are inherited muscle disorders?
Include:
- muscular dystrophy
- biochemical defects in glycogen & lipid storage
What is Duchenne muscular dystrophy?
Duchenne muscular dystrophy is a genetic disorder that results in the absence of the cytoskeletal protein dystrophin
What are the consequences of Duchenne muscular dystrophy’s absence of dystrophin?
Leads to tiny tears in the muscle fibers:
- which allow Ca ions to enter & activate enzymes
- that break down fiber components
- resulting in muscle weakness and degeneration
What is myasthenia gravis?
An autoimmune disease where antibodies are produced against the ACh receptors
What are the consequences of the autoimmune response against Ach receptors?
Results in a reduction in the number of Ach receptors at the neuromuscular junction, leading to muscle weakness and fatigue
What is the effect of curare on skeletal muscle?
Curare is a compound that binds to the ACh receptor without activating it, which results in the inhibition of muscle contraction and paralysis
What is the effect of botulism toxin on the synapse?
Botulism toxin prevents the release of the neurotransmitter into the synapse, resulting in the inhibition of muscle contraction and paralysis.
What is the effect of nerve gas on the synapse?
- inhibits AChE present in the synapse
- which leads to the accumulation of ACh & overstimulation of the muscle
- resulting in muscle spasm, convulsions, & paralysis
What is the effect of nerve gas on the synapse?
- inhibits acetylcholinerestase (AChE) present in the synapse
- which leads to the accumulation of Ach & overstimulation of the muscle
- resulting in muscle spasm, convulsions, & paralysis
