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30 Cards in this Set

  • Front
  • Back
What are the two types of striated muscle?
Two types of striated muscle:

* Cardiac
* Skeletal
List the four characteristics of skeletal muscle.
Skeletal
* Connected, via connective tissue, to bone
* Sarcomeres
* Excitation: Voluntary and neurogenic
* Type of excitation: Excitation-contraction coupling. Depolarization-induced via Ca+2 release.
What types of cells connect cardiac cells to one another?
Intercalated disks containing gap junctions.
What are the four characteristics of smooth muscle?
* Slow sustained contractions
* No sarcomeres
* Lots of joined cells
* Excitation: nerves or hormones, or each other or all three.
What three things does the sarcoplasm contain a lot of?
* Mitochondria
* Glycogen
* Myoglobin
What are the five things that make up skeletal muscle fibers?
* Long cylindrical cells
* Multiple nuclei
* Mitochondria
* Myofibrils
* Sarcoplasm
What is the function of myosin?
Myosin function: Motor protein for actin that utilizes ATP to drive movement.
Is actin a thick or thin filament?
Actin is a thick filament.
Connectins are also known as the "__ disk".
Connectins are also known as the "Z disk".
Desmin is also known as the "__ line".

What is the function of desmin?
Desmin is also known as the "M line".

Function of desmin: Connects adjacent myosin filaments.
Is Titin inelastic or elastic?
Titin is elastic.
Is nebulin elastic or inelastic?

What is nebulin's function?
Nebulin is inelastic.

Function of nebulin: Stabilizes the thin filament.
What does SER stand for?

What are the two functions of the SER?
SER = smooth endoplasmic reticulum

Functions of SER:
* Surrounds each myofibril
* Regulates intracellular levels of Ca+2
* Releases Ca+2 into the system
What is the largest protein we know of? How large is it (in Daltons)?
Titin with a molecular weight of 3E6 Daltons.
What is the sarcolemma?
The surrounding cellular membrane around the myofibrils.
What are t-tubules?
T-tubules are in-foldings within the sarcolemma.
What is the function of the sarcolemma?
Transduces action potentials from the sarcolemma to the sarcomeres.
List the four characteristics of cardiac muscle.
Cardiac
* Connected to other cardiac muscle cells
* Cardiomyocytes (single cells) with sarcomeres
* Excitation: myogenic & involuntary
* Excitation contraction coupling Ca+2 induced Ca+2 released
Myosin is also known as the "__ band".

Is myosin a thick or thin filament?
Myosin is also known as the "A band".
Is myosin a thick or thin filament?
Myosin is a thick filament.
Where is actin exclusively found?
Actin is exclusively found in the I band, and some flows into the A band.
What are the two functions of connectins?
Two functions of connectins:
* Anchors actin filaments
* Connects adjacent myofibrils
What are the two functions of titin?
Two functions of titin:
* holds the myosin filaments in place
* allows the muscle to spring back after stretching
What is the general idea of the "sliding filament theory"?
Thin filaments slide past thick filaments.
Outline the 6 molecular steps that underlie muscle contraction.
1) Myosin head is bound to actin and not bound to ATP. This is the rigor conformation. As in rigor mortis in which muscles of an animal are rigidly fixed in place because of the absence of ATP in death.

2) ATP binds to the myosin head and causes the myosin head to detach from the actin. It is the BINDING of ATP that causes the myosin head to detach from actin. The energy within ATP is not used to detach the myosin head from actin.

3) Myosin head hydrolyses ATP to ADP and inorganic phosphate, and the myosin head cocks into position while the ADP and inorganic phosphate remain bound to the myosin head. (myosin head cocking > myosin/ADP/inorganic phosphate complex). The energy released from hydrolosis of the ATP molecule is stored in the myosin/ADP/inorganic phosphate complex.

4) Inorganic phosphate is released and causes the power stroke which slides the actin past the myosin toward the center of the sarcomere.

5) At the end of the power stroke, ADP is released and the myosin (again) remains tightly bound to the actin until another ATP molecule binds to the myosin head.
What is the function of tropomyosin and troponin?
Tropomyosin and troponin both function to prevent contraction by sterically blocking myosin heads from binding with actin filaments.
What role(s) do/does tropomyosin and troponin play in muscle contraction?
In order for the muscle to contract Ca+2 needs to be present because tropomyosin and troponin physically block the myosin heads from binding to actin at rest. Troponin has a Troponin-C binding site for Ca+2 ions which, when bound to Ca+2, causes a conformational change in troponin and tropomyosin that moves both troponin and tropomyosin out of the way to allow formation of the myosin cross-bridges (myosin heads binding to actin filaments in preparation for the power stroke).
What is "excitation-contraction coupling"?
The relationship between contraction and depolarization.
Why does rigor mortis occur?
* The amount of Ca+2 in the cytoplasm remains because the dying cells of the sarcoplasmic reticulum can no longer take up the ions.

* Dead cells do not produce ATP (which releases the myosin head from binding sites on actin).
Describe all the molecular steps that occur in excitation-contraction coupling.
1) Action potential in the motor neuron triggers exocytosis of vessicles containing acetylcholine. Acetylcholine diffuses across the synaptic cleft to the motor end plate.

2) Acetylcholine binds to ligand-gated channels and open. Na+ enters the cell and causes depolarization of the motor endplate.

3) The action potential travels over the sarcolemma and eventually depolarizes the t-tubules (transverse tubules).

4) The dihydropyridine (DHPR) channels of the t-tubule change conformation in response the t-tubule having been depolarized.

5) The conformation change of DHPR causes ryanodine receptors (RYR) on the sarcoplasmic reticulum (SR) to open. Open RYR channels cause Ca+2 to flow into the cytoplasm.

6) Ca+2 in the cytoplasm binds to troponin which moves tropomyosin out of the way of cross-bridge linking between actin and myosin heads.

7) The SR uses ATP to pump Ca+2 back into the SR.

8) The decrease in cytoplasmic Ca+2 causes troponin-Ca+2 to dissociate from one another. DHPR reverts to original conformation which causes RYR closure.