Lecture 9: Anatomical Components of Muscle (Hayward)

Question 1

what property is common to all muscles?*

Answer 1

contractility

Question 2

why does skeletal muscle have banded appearance?*

Answer 2

regular arrangement of actin and myosin

Question 3

cytoplasm of muscle cell = *

Answer 3

sarcoplasm

Question 4

endoplasmic reticulum of muscle cell = *

Answer 4

sarcoplasmic reticulum

Question 5

muscle cell = *

Answer 5

myofiber

Question 6

components of myofibril*

Answer 6

actin and myosin myofilaments

Question 7

hierarchy of skeletal muscle structure*

Answer 7

myofilament –> myofibril –> myofiber –> muscle fascicle –> muscle belly

Question 8

what are a bunch of myofibrils surrounded by to make a myofiber (muscle cell)?*

Answer 8

endomysial layer

Question 9

what structure surrounds a muscle belly?*

Answer 9

fascia

Question 10

name the bands in a sarcomere*

Answer 10

A (anisotropic), I (Isotropic), M, H, and Z bands

Question 11

What happens to the length of the different bands in a sarcomere during a muscle contraction?**

Answer 11

I and H bands shorten. A and M bands stay the same length. Total sarcomere length (distance between Z bands) decreases.

Question 12

what happens to sarcomere if only one Z band contracts?*

Answer 12

no force is produced. Z bands on both ends of sarcomere must contract to produce force.

Question 13

fx of M-line*

Answer 13

anchors adjacent thick filaments (myosin)

Question 14

fx of Z bands*

Answer 14

anchor thin filaments (actin)

Question 15

H-band is composed of thick and/or thin filaments?*

Answer 15

Thick filaments only

Question 16

What are Z-lines composed of?*

Answer 16

alpha-actinin and Z-line filaments

Question 17

What are M-lines composed of?*

Answer 17

M-line filaments and creatine kinase enzyme

Question 18

intermyofibrillar space*

Answer 18

space between adjacent myofibrils. Contains SR, mitochondria, glycogen, and lipids

Question 19

alpha-actinin*

Answer 19

an anchoring filament that helps anchor thin-line filaments to the Z band

Question 20

3 intermediate anchoring filaments**

Answer 20

vimentin, desmin, and vinculin

Question 21

fx of vinculin*

Answer 21

scaffold protein that connects myofibrils adjacent to the sarcolemma to the sarcolemma

Question 22

fx of vimentin*

Answer 22

scaffold protein that extends b/w Z lines of the same sarcomere

Question 23

fx of desmin*

Answer 23

scaffold protein that hold Z-lines of adjacent myofibrils together

Question 24

fx of titin***

Answer 24

large springy globular protein that anchors M-bands and imparts a portion of passive elastic component of muscle. Connects thick myofilaments with the Z-line. Spans distance between M and Z lines. Elasticity of titin helps restore the stretched sarcomere (muscle) back to its correct length and transfers force down to the tendon.

Question 25

In which band of sarcomere is there never overlap of thin and thick filaments?*

Answer 25

H band region (thick only)

Question 26

fx of T (transverse) tubule system*

Answer 26

an invagination of surface membrane into the muscle cell. Connects to the intracellular SR and facilitates Ca release from SR following a depolarization

Question 27

dystropin**

Answer 27

cytoskeletal protein located on the inner surface of the sarcolemma. Involved in the structural integrity of the sarcolemma (anchors actin, regulates membrane proteins). Main fx = transmission of force to extracellular matrix of muscle cell.

Question 28

what happens to muscle cell in absence of dystropin?*

Answer 28

muscle cell can't generate force and degenerates. Cause of muscular dystrophy

Question 29

what enzyme is a good marker for cardiac disease/muscle death/abnormalities of skeletal muscle?

Answer 29

creatine kinase (will be elevated in muscular dystrophy)

Question 30

myostatin

Answer 30

a SKELETAL muscle growth inhibitor. If inhibited, will facilitate muscle growth. Potential cure for muscular dystrophy. Not effective in cardiac muscle.

Question 31

follistatin

Answer 31

muscle growth activator. Potential cure for M.D.

Question 32

Could myostatin regulate hypertrophy or fibrosis?

Answer 32

No. Thus, myostatin may prevent muscle wasting without causing cardiac dysfunction in cases of cardiac failure.

Question 33

where is T tubule system located?

Answer 33

at interconnection of A and I bands in the sarcolemma

Question 34

fx of Ca in sarcomere

Answer 34

allows actin and myosin to interact

Question 35

describe path of Ca from release to reuptake in sarcomere

Answer 35

wave of depolarization moves down T tubules, conformationally changes the DHP and RyR receptors, allowing Ca to be released from SR, diffuse around cell and bind to regulatory proteins before being re-taken up by longitudinal proteins of the SR via Ca ATPase

Question 36

what stimulates Ca ATPase on SR?

Answer 36

increases in intracellular Ca

Question 37

sliding filament hypothesis

Answer 37

there must be a central component (A band) that doesn't change but has the capacity to pull other bands over it. In other words, globular heads on A bands bind to thin filaments and pull other them inward. This is accomplished by the formation and breaking of bonds between actin and myosin at the crossbridges in the presence of ATP.

Question 38

conductility

Answer 38

the propagation of membrane depolarization over the cell surface

Question 39

What corresponds to the dark staining bands of muscle fibers on light microscope?

Answer 39

A-bands. Composed of parallel arrays of thick myofilaments composed of myosin. Have cross-bridges that extend toward adjacent thin myofilaments

Question 40

What corresponds to the light staining bands of fibers on light microscope?

Answer 40

I bands. (thin filaments of actin). Attach at one end to Z lines.

Question 41

sarcomere =

Answer 41

repeating Z-line to Z-line interval of myofibrils

Question 42

myofilament ratio

Answer 42

6 thin myofilaments to 1 thick myofilament. Each thick filament is surrounded by a hexagonal array of 6 thin filaments.

Question 43

2 main components of muscle membrane system that serve to activate the contractile apparatus

Answer 43

1) transverse (t) tubular system | 2) Sarcoplasmic reticulum

Question 44

What is a triad?

Answer 44

complex of T-tubule flanked by 2 terminal cisternae on the SR. There are 2 triads per sarcomere. Forms a gap which is bridged by junctional feet. A conformational change in the junctional feet leads to Ca release from the SR.

Question 45

components of junctional feet

Answer 45

DHP and RyR receptors

Question 46

sarcotubules

Answer 46

netowork of longitudinally arranged tubular membranes. Fx in re-uptake of Ca back into SR

Question 47

main fx. of SR

Answer 47

reservoir of Ca. Controls the Ca conc. of the sarcoplasm surrounding myofibrils and myofilaments through its ability to concentrate and release Ca.

Question 48

Ca ATPase pumps Ca from where to where?

Answer 48

from sarcoplasm to lumen of SR

Question 49

fx of calsequestrin

Answer 49

binds Ca. Regulated by intracellular concentrations

Question 50

How does the length of thin and thick filaments change during muscle contraction?

Answer 50

They don't change! The filaments slide over one another, but they don't actually change in length

Question 51

general fx of myosin

Answer 51

generates force of contraction, ATPase activity

Question 52

general fx of actin

Answer 52

interacts with myosin for muscle contraction, activates myosin ATPase

Question 53

general fx of alpha-actinin

Answer 53

structural; harnesses thin filaments

Question 54

general fx of tropomyosin

Answer 54

regulation; limits availability of myosin binding sites on actin

Question 55

general fx of troponin

Answer 55

regulation; calcium sensitive "switch" to initiate myosin-actin interactions

Question 56

principal protein comprising thick myofilaments

Answer 56

myosin

Question 57

principal structural protein of thin myofilaments

Answer 57

actin

Question 58

length-tension relationship

Answer 58

tension generated is directly proportional to the number of cross-bridges overlapped by thin filaments

Question 59

state of actin and myosin during rigor mortis

Answer 59

they are bound and unable to disassociate in the absence of ATP