Skeletal Muscle Flashcards
What is the largest tissue in the body that is responsive to insulin?
Skeletal muscle
When seen in the blood, what enzyme is indicative of some form of damage to the structural integrity of a muscle?
Creatine kinase
What sign of lower extremity weakness is seen as children push themselves up?
Gower sign
How does a mutation in the dystrophin gene contribute to increased creatine kinase blood levels?
Dystrophin complexes links actin of the muscle fibril to the extracellular matrix to provide strength and support to the cell membrane, and when thisis mutated the cell membrane will lose integrity and creatine kinase will leak out
In which condition does an individual developm antibodies to cholinergic receptors?
Myasthenia Gravis
To which cholinergic receptor will ACh bind on the motor plate?
Nictonic (N1) receptor
Binding of acetylcholine to its receptor on the motor plate triggers what immediate event?
The opening of ligand-gated Na+ channel
The influx of what ion into the axon terminal is required for synaptic release of acetylcholine?
Ca2+
What structure of the skeletal muscle cell is especially helpful in propagating an action potential?
T-tubules
The influx of what ion into the muscle cell is responsible for depolarization? What channels are subsequently opening by the wave of depolarization?
Sodium; Opens votalge-gated Na and K channels
Where are dihydropyridine (DHP) receptors located within the cell? What type of channel are they?
The sarcolemma; L-type voltage-gated Ca channel
What is the biochemical function of dihydropyridine receptors?
Activation of ryanodine (RyR2) receptors
Where are ryanodine (RyR2) receptors located within the cell? What type of receptor is it?
The sarcoplasmic reticulum; Calcium channels?
What is the chemical result of the opening of ryanodine receptors?
A 100-fold increase in cytosolic [Ca++]
What causes the depolarization to end?
Degradation of ACh by acetylcholinesterase
What is the advantage of having action potentials that are as narrow as those in muscle depolarization?
It allows the membrane to be stimulated again and elicit another action potential that wil lincrease the strength of contraction
What displaces tropomyosin I from the myosin-binding site on actin filaments?
Cytosolic calcium binds to troponin C, which undergoes a conformational change and causes a drop in tropinin I concentration attached to actin and displaces tropomyosin
The binding of ATP to the myosin head causes what conformational change?
The release of myosin from actin
What causes the rapid formation of the cross bridge and the subseqeunt power stroke?
The release of Pi from the myosin head
When is ADP released from the mysoin head? What is the subsequent action?
It is released at the end of the power stroke and then the myosin goes back to a rigor state
What biochemical event results in muscle relaxation?
Decrease in cytosolic calcium
What is the mechaism of cytosolic calcium decrease?
Sodium/ calcium exchanger on the plasma membrane, and reuptake into the sarcoplasmic reticulum
True or false: Energy is required for muscle relaxation?
True
What chaperone proteins bind Ca2+ in the sarcoplasmic reticulum?
Calsequestrin and calreticulin
What are the early symptoms of malignant hyperthermia?
Muscle rigidity, tachycardia, hyperthermia, metabolic acidosis, tachypnea, sweating
Malignant hyperthermia can be caused by genetic defect in what two kinds of molecules?
CACNA1s: DHP receptor and RyR1: ryanodine receptor
What is the physiology underlying malignant hyperthermia?
The release of Ca2+ into the cytosol is exaggerated and reuptake into the SR is delayed
What is the most common form of motor neuron disease in adults?
Amyotrophic Lateral Sclerosis
What causes ALS?
Progresssive motor neuron degeneration
What is the pharmologic mechanism of curare?
Competitive inhibition of ACh receptor
What is the mechanism of botox?
Interferes with ability of ACh containing vesicles to bind to presynaptic plama membrane, decreasing synaptic release of ACh and preventing muscle contraction
What are the two ways skeletal muscle increases strength of contraction?
Temporal and spatial summation
What is temporal summation? What is the result of no relaxation between stimuli?
An increase in the frequency of stimulation; tetanus
What is spatial summation?
An increase in the number of motor units recruited
What physical characteristic of a muscle is related to the tension of a muscle fiber? When is tension maximal?
Length of the muscle fiber; tension is maximal at resting length
What is the maximal resting length of skeletal muscle?
The point where the number of cross-bridges is maximized
What are the three sources of ATP for skeletal muscle contraction?
ATP phosphorylation (creatine kinase), Oxidative phosphorylation, glycolysis
Most energy used in working out skeletal muscles comes from where?
Oxidative phosphorylation
What is the preferred energy source of red muscle fibers?
Oxidative phosphorylation
What is the preferred energy source of white muscle fibers?
Glycolysis
What are the two main factors used to categorize skeletal muscle fibers?
Energy metabolism and rate of force production and shortening velocity (how quickly cells contract)
What are type I skeletal muscle fibers?
Slow-twitch oxidative
What are type IIA skeletal muscle fibers? Type IIX?
Fast-twtich oxidative; Fast-twitch glycolytic
What property determines whether or not a skeletal muscle is slow or fast twitch?
Myosin-ATPase
At approximately what point in continuous moderate exercise will fat be utilized in significant amounts to fuel skeletal muscle?
After 30 min
What is muscle fatigue?
The decreased skeletal muscle tension following previous contractile activity
What type of skeletal muscle fibers are the most resistant to fatigue?
Slow -twitch oxidative fibers
What type of skeletal muscle fiber would be primarily used in sprinting?
Fast glycolytic
What is the effect of obesity and Type 2 diabetes on skeletal muscle?
Decreases the oxidative capacity and increases triglyceride content
True or false: Skeletal muscle cells have gap junctions?
False
