2/22: Skeletal Muscle and Reflexes Flashcards
Where do muscle fibers run?
Length of skeletal muscle
What is the dark band?
A band
What is the light band?
I band
What is the functional unit of cardiac and skeletal muscle?
Sarcomere
What components makes up skeletal muscle?
A. Whole muscle
B. Muscle fascicles
C. Muscle fibers (cells)
D. Myofibrils
E. Myofilaments (thick and thin) arranged in sarcomeres
What do alternating A bands and I bands create?
Striated appearance in skeletal and cardiac muscle
What is the composition of A band?
Entire length of thick filaments
What is the composition of I band?
Only thin filaments
What is the composition of H zone?
Only thick filaments
What is the composition of Z line?
Thin filaments anchored here
What is the composition of M-line?
Link the central regions of thick filaments
When do sarcomeres shorten?
During contraction
What does the muscle look like during contraction?
- zone of overlap increases
- I band decreases
- H zone decreases
- A band stays the same
What is the thin filament composed of?
Actin (with G-actin molecules), tropomyosin, and troponin
What is the active site which binds myosin?
G-actin molecules
What does troponin bind?
Actin, tropomyosin, and calcium
What makes up thick filaments?
Myosin
Describe the cross-bridges of the thick filament?
Multiple cross-bridges where the “heads” can bind to the G-actin molecule
What functions as an ATPase enzyme?
Myosin
What are the globular proteins of troponin?
T, C, and I
What does dystrophin protein connect?
Thin filaments to glycoproteins in sarcolemma
What does dystrophin-glycoprotein complex provide?
Scaffolding for sarcomeres
What are muscular dystrophies?
A. Duchenne
B. Beckers
C. Myotonic
D. Oculopharyngeal
E. Limb girdle
What does the alpha motor neuron release?
ACh
What does the alpha motor neuron bind to?
A nicotinic ACh receptor on the muscle fiber
What does botulinum toxin A inhibit?
The release of ACH at the neuromusclar junction
What is botox used for in dentistry
Bruxism, sialorrhea, masseteric hypertrophy
What are the 3 phases of a muscle twitch?
Latent, contraction, relaxation
What must happen for contraction to occur?
The intracellular calcium in the muscle fiber must increase
What does tropomyosin prevent in resting muscle?
A strong bond between the myosin head and G-actin molecules
What happens when troponin binds to cytosolic Ca++?
Tropomyosin is pulled away from the myosin binding site, and allows for the power stroke
What is released from the sarcoplasmic reticulum?
Calcium
What is the sarcoplasmic reticulum?
Modified ER that sequesters Ca2+
What is transverse (T)-tubules?
Invaginations of sarcolemma
What is terminal cisternae?
Portion of SR that contact T-tubule
Where does the AP travel?
Down T-tubules and activates voltage-sensitive dihydropyridine (DHP) receptors on the T-tubules
What happens when the voltage-sensitive dihydropyridine receptors are activated?
The calcium channels (ryanodine receptors) open on the SR
What happens when the calcium channels open?
Goes from SR to the sarcoplasm
What does the intracellular structure of myocytes ensure?
The spread of action potential (and calcium) throughout the cell
What is ATP necessary for?
Contraction
What does ATP binding to the myosin head cause?
A break in the cross-bridge (connection between actin and myosin)
What does energy release from ATP hydrolysis by the myosin head provide?
Energy for cocking the myosin head (myosin is now in the high energy form)
What does release of inorganic phosphate from the myosin head provide energy for?
The power stroke
What is the power stroke?
Myosin head pulling actin towards the center of the sarcomere
What shortens the sarcomere?
The power stroke
Muscle cells only have enough ATP for how many twitches?
~8
What produces ATP for muscle fibers?
A. Aerobic and anaerobic metabolism
B. Phosphocreatine
What does contribution of aerobic and anaerobic metabolism on each specific muscle depend on?
(1) the metabolic enzymes are present in the cell (ex. glycolytic
fibers versus oxidative fibers)
(2) the intensity of the exercise
What are measurements of creatine kinase levels in the blood done to determine?
If damage to muscle tissues (skeletal and cardiac) has occurred (ex: heart attack or muscular dystrophy)
What 3 things are associated with fatigued muscles?
1.have decreased tension generation,
2.take longer to contract
3.relax more slowly and may not completely
relax
What are theories that lead to fatigue?
1.Change in membrane potential
2.Decreased ACH
3.Blockage of blood flow
4.Central Fatigue
5.Increased metabolic byproducts
6.Depleted glycogen
What must be present for cross-bridge cycling?
both calcium AND ATP
Describe the steps of the cross-bridge cycling (sliding filament theory)
A. Rigor State: myosin and actin are tightly bound
B. ATP binds myosin, decreases its affinity for
actin, and the two separate
C. Myosin head moves in the direction of the Z line,
ATP is hydrolyzed
D. Myosin binds the next actin (one closer to Z line)
and power stroke occurs (pulls actin toward the
M Line)
E. ADP is released and the actin and myosin
resume the brief rigor state
