Skeletal Musle Contraction

Question 1

CapZ and A actinin?

Answer 1

Serve to anchor the thin filament to the Z line

Question 2

What is desmin?

Answer 2

extends along the Z line to integrin proteins. It contributes to keeping lateral sarcomeres on the same axis (alignment of sarcomeres across muscles) and the lateral transmission of force.

Question 3

What are myotendinous junctions?

Answer 3

They transmit force of contraction longitudinally to the tendon. It’s very important because the nature of muscle changes, going from muscle cells to elastic cells. Malfunctions of this region can lead to muscular dystrophy. It transmits the force longitudinally together with the titin protein.

Question 4

What are costameres?

Answer 4

They transmit the force of contraction laterally to the connective tissue

Question 5

What do Titins do?

Answer 5

Anchors thick filaments to the Z line. It’s an elastic protein that extend from the Z line to the center of the sarcomere. Its main role is to align sarcomeres, together with desmin

Question 6

what is SERCA?

Answer 6

a pump connected to the membrane of the SR and plays an important role in removing the Ca+2 from inside the cell and to the reticulum

Question 7

what is triad?

Answer 7

In the histology of skeletal muscle, a triad is the structure formed by a T tubule with a sarcoplasmic reticulum (SR) known as the terminal cisterna on either side. Each skeletal muscle fiber has many thousands of triads, visible in muscle fibers that have been sectioned longitudinally

Question 8

H-zone

Answer 8

only thick filaments (myosin). Shrinks during contraction

Question 8

A- band

Answer 8

actin and myosin together overlapping (whole length of thick filaments)

Question 9

I-band

Answer 9

only thin filaments (actin). Shrinks during contraction.

Question 9

The binding of cytosolic Calcium (Ca inside of the cell) with __________, promotes the movement of tropomyosin, uncovering the sites for the interaction between thin and thick filaments and contraction can start. At this point the myosin head interacts with the active site

Answer 9

troponin C

Question 9

M-line

Answer 9

myosin connecting. Contains proteins critical for the alignment of the thick filaments in the sarcomere.

Question 10

Control of neurotransmitter concentration in the synaptic cleft in 3 mechanisms:

Answer 10

Reuptake.
Enzymatic degradation.
Diffusion away from the synapse.

Question 10

to which receptors do Acetylcholine molecules bind in the muscles?

Answer 10

Nicotinic receptors

Question 10

______________- drug indirect antagonist of Ach, causing muscle paralysis. It also blocks the Ach vesicles with presynaptic membrane blocking their release. Produced by Chlostridia

Answer 10

Botulinum toxin

Question 10

Z- line

Answer 10

connection of thin filaments. provide a structural role, since all the actin filaments are linked to it.

Question 10

structure of Actin filaments?

Answer 10

it is formed by G-actin (monomer), they assemble to form F-actin. F-actin consists of two stranded helical filaments, that contain troponin and tropomyosin.

Question 11

Structure of Myosin filaments?

Answer 11

Two large “heavy” chains that form a double helix and constitute the tail of the myosin molecule.
Four small “light” chains that stabilize the structure of the myosin heads or cross-bridges.
Myosin light chains (MLCs), which can be classified into two groups: essential or alkali MLC (MLC1 or ELC) and regulatory MLC (MLC2 or RLC).
A single myosin molecule consists of two myosin heavy chains (MYHs), which interact with two pairs of myosin regulatory light chains and myosin essential light chains to form a hexamer

Question 12

Mechanism mediated by calcium. As the action potential reaches the T tubule, it leads to a change of the potential inside the T tubule, detected by the _______________ receptor (L‐type voltage‐gated Ca2+ channel), located inside the T tubule. This receptor changes the conformation and is directly related (physically coupled) to the ____________receptor, located at the level of the membrane of terminal cisternae (Ca+2) storage, allowing the efflux of calcium

Answer 12

DHP (dihydropyridine), RyR (ryanodine)

Question 12

Troponin complex is composed of 3 subunits:

Answer 12

A- binds to affinity for actin.
T- binds to tropomyosin.
C- binds to Calcium.

Question 13

What does Nebulin do?

Answer 13

extends from the Z line along the length of thin filament and may participate in regulation of its length

Question 13

What does Tropomodulin do?

Answer 13

located at the end of thin filaments, toward the center of the sarcomere, and participate in setting the length of the thin filaments.

Question 14

Fatigue of the neuromuscular junction- if fiber Stimulation is higher than _____ pulses/sec it may diminish the number of Ach vesicles in a rate that causes impulses fail to pass into the muscle fiber

Answer 14

100

Question 15

The resting membrane potential of skeletal muscles is _____mV more negative than in neurons, so around _______mV

Answer 15

10-20, 80-90

Question 15

__________- drug direct antagonist of Ach, inhibiting Ach receptors by binding to them. Could cause muscle paralysis

Answer 15

Curare poison

Question 15

________ receptor is a complex of 5 subunit proteins(2 binding sites)

Answer 15

Acetylcholine

Question 16

Enzymatic degradation- ____________ destroys Ach. These processes prevent continued muscle re-excitation after the muscle fiber has recovered from its initial action potential. The few msec Ach remains in the synaptic space is enough to excite the muscle fibers

Answer 16

acetylcholinesterase

Question 17

_____________ protein- has a kind of storing function, allowing the accumulation of Ca+2 close to the terminal cisternae, where it is then released

Answer 17

Calsequestrin protein

Question 17

___________another Na+-Ca+2 antiporter (ATPase) located on the sarcolemma pumps calcium to the ECF

Answer 17

NCX-

Question 18

________________- Ca+2 pump, involved in the uptake of Ca, moving it from the sarcoplasm to the SR, allowing the decrease of Ca+2 in the extracellular space, by using ATP

Answer 18

SERCA protein

Question 19

Each ____ induces 1 simple twitch (contraction- relaxation cycle). It depends on movement period because maintaining Ca+2 intracellular concentration induces further cycling

Answer 19

AP

Question 19

__________ has 4 binding sites for Ca

Answer 19

Troponin C

Question 19

steps of muscle contraction:

Answer 19

1) Ca released from the SR binds to troponin which then releases tropomyosin from the actin 2) myosin heads bind to the actin 3) it then releases ADP and P which causes the power stroke 4) ATP binding to myosin decreases the affinity to actin, causing it to release from it

Question 20

_________ and _________- bind both RYR and calsequestrin. Both regulate Ca+2 release, ensuring efficient release and avoiding excess (controlled release).

Answer 20

Triadin, junctin

Question 21

what is rigor mortis?

Answer 21

hardening of skeletal muscles due to the absence of ATP

Question 22

isometric contraction?

Answer 22

measuring the tension of muscle at a certain length (muscle does not shorten during contraction).

Question 23

isotonic contraction?

Answer 23

measuring the length of muscle at a certain tension. (muscle shortens)

Question 24

what determines the muscle strength?

Answer 24

Number of actin‐myosin cross‐bridges, Diameter of the fibers. Length of the sarcomeres. Amount of calcium that binds to troponin. The myosin isoforms (type I/type II). -The passive tension generated by the elastic structures of the fiber. -Diameter of the fibers- sarcomeres arranged in parallel

Question 25

optimal length of sarcomeres?

Answer 25

2-2.2 μm

Question 26

The total force developed by a muscle is the sum of the tension generated by the ___________ and ____________ generated by the elastic structures of the fiber (connective tissue).

Answer 26

sarcomeres, the passive tension

Question 27

what determines the velocity of sarcomere shortening?

Answer 27

Applied load. Myosin ATPase activity. -Applied load- A fiber can shorten if the applied load is less than the maximum isometric force it is capable of generating (force-velocity relationship).

Question 28

Also [Ca2+] in the muscle plays a role in determining which myosin isoform is expressed in the muscle fiber. -E.g. lateral rectus that responds quickly to the arrival action potential is called _____________muscle fibers the soleus, responding within a longer time and relaxes slowly to the arrival of the same action potential, is called______________muscle fibers

Answer 28

fast twitch, slow twitch