Skeletal Muscle Contraction

Question 1

What is the structure of skeletal muscle?

Answer 1

Composed of cylindrical muscle fibers
Bundle of fibers - fascicle
Endomysium surrounds each fascicle

Question 2

Where do the striations arise from?

Answer 2

Repeating pattern of light and dark bands due to arrangement of thick and thin filaments within myofibril

Question 3

What do thin filaments contain?

Answer 3

Actin
Anchored to Z lines at each end of a sacromere

Question 4

What do thick filaments contain?

Answer 4

Myosin
In A band at center of sacromere

Question 5

Which band is the dark and light band?

Answer 5

A - dark band
I - light band

Question 6

What is the mechanism of contraction?

Answer 6

Thin filaments propelled toward center of their sarcomere by movements of myosin cross bridges that bind to actin

Question 7

What do the 2 globular heads of each cross bridge contain?

Answer 7

Binding site for actin and enzymatic site that splits ATP

Question 8

What are the 4 phases of the cross bridge cycle?

Answer 8

1. Cross-bridge formation; release of Pi
2. Power stroke, ADP released, myosin undergoes conformational change
3. ATP binds myosin, detachment of myosin from actin, cross-bridge dissociates
4. ATP hydrolysis occurs, cocking myosin head

Question 9

What is the function of tropomyosin?

Answer 9

Tropomyosin protein coils around Actin helically and attaches via Troponin complex
Ca2+ is trigger

Question 10

What is the function of the Ca2+ ions?

Answer 10

Bind to troponin, producing a change in shape transmitted via tropomyosin to uncover binding sites on actin, allowing cross bridges to bind to thin filaments

Question 11

How is the action potential propagated?

Answer 11

Along t tubules to sarcoplasmic reticulum where it releases Ca2+

Question 12

What is relaxation caused by?

Answer 12

Active transport of cytosolic calcium ions back into SR

Question 13

What is an adaption to t tubules?

Answer 13

Presence of continuous invaginations along SR allows for effective contraction

Question 14

What is the structure of the triad junction?

Answer 14

Central t-tubular element flanked on either side by a terminal cisternae
Occurs at every Z line

Question 15

How does depolarization occur?

Answer 15

Voltage dependent activation and conformational change of subunits of the L-type Ca2+ channel or DHPR

Question 16

What are L-type voltage gated Ca2+ channels linked to?

Answer 16

RyR receptors

Question 17

What is the role of DHPR?

Answer 17

Voltage sensor
Transmits signal to RyR four subunits

Question 18

What is the role of the alpha 1 subunits?

Answer 18

Voltage sensing and pore forming subunit

Question 19

What is the role of the beta 1a subunit?

Answer 19

Indispensible for EC coupling
Surface expression of DHPRs and tetrad formation

Question 20

What are the 4 main proteins responsible for Ca2+ cycling and storage within SR?

Answer 20

DHPR, RyR1, SERCA pump and calsequestrin

Question 21

What is calsequestrin?

Answer 21

High capacity Ca2+ binding protein found in terminal cisternae of SR

Question 22

What is the Ryanodine receptor?

Answer 22

Ligand gated channel and forms a homotetramer
Largest known ion channel
Highly clustered

Question 23

What does the N-terminal domain of RyR receptors contain?

Answer 23

Binding sites

Question 24

What does the C-terminal domain of RyR receptors contain?

Answer 24

Transmembrane domains
Ion-conducting pore

Question 25

What are the junctional feet of the SR?

Answer 25

Possibly communicate between surface and internal membranes
4 DHPRs link to a subunit of an underlying foot