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80 Cards in this Set

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What are DHPR's and what is their role?
V-gated Ca2+ channels located in the T-tubule.
Closely associated with RyRs
Open with depolarization and activate RyRs
What are RyRs and what is their role?
Macromolecular proteins in the junctional SR.
Function as Ca2+ release channels.
Span the gap between SR and T-tubules.
Mechanically activated by DHPRs in T-Tubules.
Describe the arrangement of myofilament proteins.
Lattice of thick (myosin) and thin (actin) filaments arranged in sarcomeres.
Z-lines connect __?
Actin filaments
A-bands?
Dark A-bands of sarcomere indicate overlap of myofilaments.
Contraction in muscle is produced by sliding of ___ past each other causing the ___ to shorten.
Myofilaments
Sarcomere
Myosin globular heads bind to ?
Actin
What provides the E for the power stroke in muscle contraction?
ATP hydrolysis
What triggers contraction in skeletal muscle?
A rise in the concentration of Calcium inside the myofibril.
What property do all muscle types have in common?
All muscles TRANSDUCE chemical or electrical commands into mechanical responses. (contraction)
What are DHPR's and what is their role?
V-gated Ca2+ channels located in the T-tubule.
Closely associated with RyRs
Open with depolarization and activate RyRs
What are RyRs and what is their role?
Macromolecular proteins in the junctional SR.
Function as Ca2+ release channels.
Span the gap between SR and T-tubules.
Mechanically activated by DHPRs in T-Tubules.
Describe the arrangement of myofilament proteins.
Lattice of thick (myosin) and thin (actin) filaments arranged in sarcomeres.
Z-lines connect __?
Actin filaments
A-bands?
Dark A-bands of sarcomere indicate overlap of myofilaments.
Contraction in muscle is produced by sliding of ___ past each other causing the ___ to shorten.
Myofilaments
Sarcomere
Myosin globular heads bind to ?
Actin
What provides the E for the power stroke in muscle contraction?
ATP hydrolysis
What triggers contraction in skeletal muscle?
A rise in the concentration of Calcium inside the myofibril.
What property do all muscle types have in common?
All muscles TRANSDUCE chemical or electrical commands into mechanical responses. (contraction)
Broad functions of muscle types:
1) Skeletal
2) Cardiac
3) Smooth
1) Posture, Voluntary Movement
2) Rhythmic contraction to maintain BP
3) Peristalsis, Vascular Tone, Sphincter Muscles
What physiological properties should be considered regarding the suitability of a particular muscle type for its function?
1) Velocity of contraction
2) Duration of contraction
3) Fatigability of contraction
Skeletal muscle-
Velocity?
Duration?
Fatigability?
Rapid force development.
Relatively long duration.
Variable fatigue.
Cardiac muscle-
Velocity?
Duration?
Fatigability?
Rapid force development.
Very short duration.
No fatigue.
Smooth Muscle-
Velocity?
Duration?
Fatigability?
Slow force development and range of forces.
Some long duration.
No fatigue.
How does electrical excitation occur in skeletal muscle?
Electrical excitation is achieved here by motor nerve activation.
How does electrical excitation occur in cardiac muscle?
Initiated from SA node.
Cells electrically coupled via gap junctions.
Nerves only MODULATE contraction.
How does electrical excitation occur in smooth muscle?
Can be excited by nerves or by electrical coupling to neighboring cells.
ECC = ?
Excitation- Contraction Coupling
How electrical excitation leads to rise in Calcium resulting in contraction.
The process of ECC is ___ amongst the 3 basic muscle types.
Different
How is an action potential produced in skeletal muscle from the release of ACh at the motor end plate?
ACh causes activation of nAChRs at postsynaptic membrane of the muscle causing EPP causing AP if threshold is reached.
This is more organized in skeletal muscles than in cardiac muscles.
Myofibrils
What are the 3 noticeable features of skeletal muscle ultrastructure?
1) T-Tubules
2) Sarcoplasmic Reticulum
3) Organization of Myofibrils
What is the function of T-tubules in skeletal muscle?
Invaginations of muscle sarcolemma at A-I junctions (Z-lines in cardiac) where AP is projected down into muscle.
This is much more extensive in skeletal muscle than cardiac muscle.
Sarcoplasmic Reticulum
What is the function of the SR in skeletal muscle?
Storage of Calcium for contraction.
What is a triad?
T-tubules form tight junctions with two terminal cisternae.
Cisternae
end of sarcoplasmic reticulum
What is the equivalent structure to a triad called in cardiac muscle?
Dyad
Only 1 terminal cisternae adjoining T-tubules.
These are the "feet" connecting the T-tubules to the SR.
Ryanodine Receptors (RyRs)
Broad functions of muscle types:
1) Skeletal
2) Cardiac
3) Smooth
1) Posture, Voluntary Movement
2) Rhythmic contraction to maintain BP
3) Peristalsis, Vascular Tone, Sphincter Muscles
What physiological properties should be considered regarding the suitability of a particular muscle type for its function?
1) Velocity of contraction
2) Duration of contraction
3) Fatigability of contraction
Skeletal muscle-
Velocity?
Duration?
Fatigability?
Rapid force development.
Relatively long duration.
Variable fatigue.
Cardiac muscle-
Velocity?
Duration?
Fatigability?
Rapid force development.
Very short duration.
No fatigue.
Smooth Muscle-
Velocity?
Duration?
Fatigability?
Slow force development and range of forces.
Some long duration.
No fatigue.
How does electrical excitation occur in skeletal muscle?
Electrical excitation is achieved here by motor nerve activation.
How does electrical excitation occur in cardiac muscle?
Initiated from SA node.
Cells electrically coupled via gap junctions.
Nerves only MODULATE contraction.
How does electrical excitation occur in smooth muscle?
Can be excited by nerves or by electrical coupling to neighboring cells.
ECC = ?
Excitation- Contraction Coupling
How electrical excitation leads to rise in Calcium resulting in contraction.
The process of ECC is ___ amongst the 3 basic muscle types.
Different
How is an AP produced in skeletal muscle from the release of ACh at the motor end plate?
ACh ->
Activation of nAChRs at postsynaptic membrane of the muscle ->
EPP ->
AP if threshold is reached
This is more organized in skeletal muscle than in cardiac muscle.
Myofibril organization.
What are the 3 noticeable features of skeletal muscle ultrastructure?
1) T-Tubules
2) Sarcoplasmic Reticulum
3) Organization of myofibrils
What is the function of T-Tubules in skeletal muscle?
Invaginations of muscle sarcolemma at A-I junctions (Z-lines in cardiac) where AP is projected down into muscle
What is the function of Sarcoplasmic Reticulum in skeletal muscle?
Store of Calcium for contraction.
What is a triad?
T-Tubules form tight junctions with two terminal cisternae.
Cisternae
End of Sarcoplasmic Reticulum
What is the structure equivalent to a triad in cardiac muscle?
Dyad
Only 1 terminal cisternae adjoining T-Tubules.
These "Feet" connect the T-Tubule to the Sarcoplasmic Reticulum.
RyRs
Where are RyRs located?
What is their function?
Location- spanning the gap between the SR and T-Tubules.
Function- Calcium release channels. Pass calcium from SR to T-Tubules.
What are the important dimensions of a RyRs?
Extends 12 nm from SR membrane.
Gap between SR and T-Tubule is 15 nm so RyRs goes almost the entire distance.
What type of receptor is a Dihydropyridine Receptor?
DHPRs
L-Type Calcium Channels
What is the structure and location of DHPRs?
Arranged in clusters of 4.
Positioned over every other RyRs. (Not random!)
What is the overall ratio of RyRs to DHPRs?
1:2
What is the mechanism of ECC coupling in skeletal muscle?
The DHPR and RyRs are mechanically coupled.
How does an AP in the T-Tubule lead to Calcium release?
Deplarization in T-Tubule ->
Opens DHPRs (mechanically coupled to RyRs) ->
Opens RyRs ->
Calcium Release
What part of the DHPR interacts with the RyR?
II-III Intracellular Loop
Is Calcium entry through DHPRs required to trigger Calcium release from the RyR?
NO. Its the physical interaction of the proteins that matters, not the Calcium entry.
In what sense is EC coupling in skeletal muscle V-Dependent?
We have to depolarize to open DHPRs which in turn open RyRs.
In what sense is EC coupling in skeletal muscle not V-Dependent?
Once DHPRs are open.
With large depolarizations, we -> Nernst potential for Calcium. It becomes more and more positive inside the cell. The driving force for Calcium decreases, but is irrelevant because Calcium entry is not required.
Because Calcium entry is not required for contraction in skeletal muscle, this implies that ____ is the primary source of Calcium for contraction.
Sarcoplasmic Reticulum
(We dont care about Calcium coming into the cell because its already in the cell in the SR.)
Not all RyRs are coupled with DHPRs. How are these uncoupled RyRs activated?
Calcium induced Calcium release.
How does Calcium induced Calcium release work?
Unpaired RyRs are triggered by the release of Calcium from neighboring coupled RyRs.
This is extremely important in Cardiac muscle and less so in skeletal.
Calcium induced Calcium release.
How is contraction terminated?
By removing Calcium from the cytosol.
How is calcium pumped out of the cytosol to terminate muscle contraction?
Pumped back into SR via Calcium-ATPase. (aka SERCA because its also found in smooth ER)
What are the triggereing agents of Malignant Hyperthermia?
Succinylcholine or volatile anesthetics such as halothane
What are the symptoms of Malignant Hyperthermia?
Tachypnea
Low plasma O2, high CO2
Tachycardia
Rigidity
Swings in BP
Muscle Breakdown
What is the cause of Malignant Hyperthermia?
Basically high intramuscular Calcium release.
Mutation in RyRs causes increased activation/ reduced deactivation so ATP is consumed pumping out the Calcium from the cytosol leading to the generation of heat.
Compared to cardiac muscle, the ultrastructure of skeletal muscle is different in what way?
The SR is more extensive in skeletal muscle.