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73 Cards in this Set

  • Front
  • Back
What is the basic principle on which muscles work?
A lever system
What types of proteins make up muscles?
What are the contractile proteins in muscle?
What are the main structural proteins in muscle?
-Alpha actinin
What does Titin do?
Maintains the spacing between thick filaments and structural alignments of the sarcomere
What does Nebulin do?
Controls the width of thin filaments
What do Cap Z and Alpha Actinin do?
They tie the thin filaments to the Z line.
What is the functional unit of a muscle?
What fuzz covers a muscle cell on micrograph?
Connective tissue
What does connective tissue do to muscle?
Gives it elastic passive force so that if you stretch the muscle it will generate a lot of force just by nature of its passive elasticity.
In the sarcomere, what is the Z-line?
The boundary where Actin is attached
What is the I band?
Region of thin filaments only
What is the A band?
The region where thick/thin filaments overlap
What is the H zone?
The region of only thick filaments
What is the M line?
The center of the H zone where there are structural proteins.
What line disappears when the muscle contracts?
The I band
What is each myosin filament composed of?
Many myosin molecules.
What is a myosin molecule like structurally?
Consists of 6 components:
-2 Heavy chains (helical)
-4 light chains
How are the heavy chains arranged?
Into a tail and head
How many light chains area associated with each head of a myosin molecule?
What are the light chains called?
2 = regulatory
2 = essential
What makes the essential light chains essential?
They are essential for the sliding filament mechanism.
Are regulatory light chains very important in skeletal muscle?
What 3 molecules make up the thin filament?
What is the structure of Actin like?
It is a helical filamentous molecule, made up of 2 globular actins.
Why is Actin important?
Because the active sites for crossbridge formation are on Actin.
How many molecules make up the Actin filament (not molecule)?
-2 Actins (2 gs -> f)
-2 Tropomyosins
-1 Troponin
What is absolutely essential for the sliding mechanism to work?
How does Calcium cause muscle contraction?
It binds Troponin-C, which allows tropomyosin to move out of the way of the active sites on Actin so crossbridges form.
What happens when Calcium binds troponin-C?
Crossbridge formation occurs, then phosphate and ADP are released from myosin.
What must happen after ADP is released from myosin during the sliding filament mechanism?
ATP must bind and be hydrolysed again in order to prevent rigor mortis.
So what are the 3 roles of ATP in skeletal muscle?
1. Providing the chemical energy that ultimately gets converted to muscle force
2. Preventing Rigor mortis and stopping contraction
3. Pumping calcium back out into the SR via maintaining ionic gradients.
What is the sarcolemma?
The external cell membrane of a muscle fiber
What are the internal membrane systems in striated muscle?
-Transverse tubules
-sarcoplasmic Reticulum
What is a Triad?
A t-tubule with the SR's terminal cisternae on either side.
What important exchanger resides in the sarcolemma?
Na/K ATPase
What is the T-tubule system?
An invagination of the external cell membrane
Why is the SR important?
That's where calcium is stored for muscle contraction.
At the NMJ for skeletal muscle what is the:
NT = Acetylcholine
Receptor = nicotinic cholinergic
What is the receptor on smooth muscle for impulses transmitted by the vagus nerve?
Muscarinic cholinergic
What happens for every motor nerve Action potential that crosses the NMJ?
It causes an AP in the muscle fiber that spreads over the cell and leads to coordinated calcium release from the SR.
What is a motor unit?
The combination of the motor nerve and all of the muscle cells that it innervates.
Does one motor nerve innervate just one muscle cell?
No; it innervates many muscle cells, in several different fascicles.
Why is it good that motor nerves innervate multiple muscle fibers?
It ensures that when the signal is sent from the brain to contract the muscle, it will happen.
What are small motor units used for?
Fine-detail tasks like surgery or writing
What are large motor units used for?
Nondetailed movements like walking or pushing your car out of the ditch.
What is ACh stored in at the ends of motor nerves?
What causes the motor nerve to release ACh for contraction?
The opening of voltage-gated Ca channels in the end of the motor nerve axon.
What happens when calcium influxes?
It binds calmodulin and results in vesicle docking to the membrane, exocytosis, and spilling of ACh into the synaptic cleft.
What causes calcium to go into the nerve terminal?
The fact that there's normally a huge gradient for calcium influx bc intracellular calcium is LOW and extracellular Ca is high.
What happens as a result of ACh release into the NMJ?
It binds the ACh receptor, which is a sodium channel that opens, and causes end plate potential to change in the muscle fiber.
Why is such a huge amount of ACh released at the NMJ into such a small area?
To ensure that when ACh is released, it will activate the receptors.
What prevents ACh from hanging around and activating the ACh receptors continually?
What is an anti-cholinesterase?
Nerve gas
Why is nerve gas deadly?
Because NMJ transmission continues to occur and is not stopped.
In what disease is Anti-AChesterase an important therapeutic agent?
Myasthenia gravis
Why give Anticholinesterase for myasthenia gravis?
Because it keeps ACh around longer so that even though receptors are auto-Ab bound and lower in concentration, those that are available WILL get some action.
Do AP's carried by motor nerve axons generate EPPs and IPPs in muscle fibers?
NO; every AP guarantees an AP in the muscle.
2 toxins that block APs at the NMJ:
-Botulinum toxin
What exactly does Curare block?
The nicotinic cholinergic receptor on the muscle cell
What does Botulinum block?
ACh release from the presynaptic terminal
2 things that Excitation-contraction coupling is vitally dependent upon in muscle fibers:
-Changes in membrane potential
-Internal membrane systems of the muscle fiber
What membrane systems are essential for efficient EC coupling in STRIATED muscle?
Which internal membrane system does an AP generated by the NMJ travel down?
The t-tubule
So what drug blocks the ACh receptor? What is it used for?
Curare - used as a muscle relaxant for surgery
What drug is used to treat Myasthenia gravis and why?
Neostigmine - bc it keeps ACh around longer by blocking ACHesterase
What warfare agent is an Anticholinesterase?
Nerve gas
What is the hollywood drug of choice and why?
Botulinum toxin - interferes with ACh release from the presynaptic terminal and keeps your face smooth and paralyzed.
What does the T-tubule do for EC coupling?
It allows the AP to penetrate deeply into the muscle to allow for coordinated contraction of the whole muscle.
How do the T-tubules couple the AP from the sarcolemma to muscle contraction?
When the AP traverses the T-tubule, it opens voltage gated Ca channels which is transmitted by foot proteins to ryanodine sensitive Ca channels in the SR that open and allow calcium influx.
What is calsequestrin?
A protien in the SR that binds calcium as it is resequestered during the end of a contraction so that the CA ATPase pump doesn't need as much energy.
What disease results when the SR calcium channels fail to close properly?
Malignant hyperthermia
When does Malignant hyperthermia become apparent?
Under volatile anesthetic conditions.