Lecture 1: Skeletal muscle part 1

Question 1

Are skeletal muscles striated?

Answer 1

yes

Question 2

Are skeletal muscles under voluntary control?

Answer 2

yes

Question 3

Shape of skeletal muscle

Answer 3

multiple peripheral cells

Question 4

Shape of a skeletal muscle?

Answer 4

long, cylindrical cells, single

Question 5

What are the three main types of muscle?

Answer 5

skeletal
cardiac
smooth

Question 6

What are skeletal muscles?

Answer 6

attached to bones and is responsible for movement

Question 7

What are cardiac muscles?

Answer 7

forms the bulk of the heart mass and its contraction ejects blood from the organ

Question 8

Smooth

Answer 8

mainly lines hollow organs, iris, blood vessels (regulates their dimensions)

Question 9

Are cardiac muscles under voluntary control?

Answer 9

no

Question 10

Are cardiac muscles striated?

Answer 10

yes

Question 11

What are the shape of cardiac muscle cells

Answer 11

branched cells with 1-3 central nuclei

Question 12

How are cardiac muscles connected?

Answer 12

they are connected by intercalated discs

Question 13

Where are cardiac muscles located?

Answer 13

in the heart ONLY

Question 14

What control are smooth muscles under?

Answer 14

involuntary

Question 15

what is the shape of a smooth muscle?

Answer 15

spindle shaped, uninucleated cells

Question 16

Are smooth muscle cells striated?

Answer 16

no

Question 17

Where are smooth muscle cells found?

Answer 17

in the gut, respiratory system, blood vessels

Question 18

What is a motor unit?

Answer 18

a group of muscle cells which is innervated by a single motor neuron

Question 19

what are the two major groups of proteins which are responsible for muscle contractions in all 3 muscle types?

Answer 19

actins

myosins

Question 20

List in order the skeletal muscle is packaged

Answer 20

1.) skeletal muscle is attached to the bone by a tendon
it is wrapped by epimysium
2.) the skeletal muscle contains bunches of fascicles (perimysium surrounded)
3.) fascicles encase bundles of muscle fibres/cells (endomysium)
4.)muscle fibres encase myofibrils
5.) myofibrils encase filaments

Question 21

What is the structure of a muscle cell?

Answer 21

sarcolemma (plasma membrane)

sarcoplams (like cytoplasm)

t tubule (invaginations of the sarcolemma towards the centre of the myofibril; open to sarcoplasm)

Question 22

Structure of a myofibril?

Answer 22

surrounded by a sarcoplasmic reticulum (SR); stores Ca2+

triad is formed when 2 terminal cisternae and a T tubule meet

Question 23

What is the sarcomere?

Answer 23

the smallest unit of contraction

from Z to Z band

Question 24

Describe cross bridge formation, what are the 4 stages?

Answer 24

Cross bridge formation
power stroke
detachment
energization of myosin head

Question 25

What happens during cross bridge formation?

Answer 25

the energized myosin head binds to a receptor site on the actin molecule forming a cross bridge inorganic phosphate is released the bond between actin and myosin become stronger

Question 26

what happens during power stroke?

Answer 26

ADP is released the inactivated myosin head pivots sliding the thin myofilament toward the centre of the sarcomere

Question 27

What happens during cross bridge detachment?

Answer 27

ATP binds to the myosin head the link between the actin and myosin weakens the myosin head detaches

Question 28

What happens during the reactivation of myosin head?

Answer 28

ATP is hydrolyzed to ADP and inorganic phosphate on the myosin heaed the energy released during hydrolysis reactivates the myosin head returning it to cocked position

Question 29

What is the structure of thick filaments?

Answer 29

composed of molecules of myosin mainly has a tail and a head the tail is oriented towards the M line

Question 30

What are thin filaments made of?

Answer 30

double stranded helical actin chain accesory proteins which regulate them: troponin tropomyosin

Question 31

What is the sliding filament model?

Answer 31

the Z line is pulled to the M line the I band and the H zone become narrower as sarcomeres shorten A bands do not change in length

Question 32

How does calcium regulate contraction?

Answer 32

as the sarcoplasm is depolarized Ca2+ channels will open in the SR thus releasing ions into the sarcoplasm, increasing the Ca2+ levels this will cause more Ca2+ to bind to troponin to enable it to change its conformation, to enable tropomyosin to expose myosin binding sites on actin

Question 33

What influences the muscle contaction?

Answer 33

the amount of Ca2+ in the cytosol

Question 34

What is the optimum length of sarcomere for max tension?

Answer 34

2. 2 micro metres | 2. 0 - 2.2 micrometres

Question 35

What happens when the length of a sarcomere is less than 2.2 micro metres?

Answer 35

the Z discs will crumple the thick filaments, less myosin head will be able to bind to actin

Question 36

What happens when the length of a sarcomere is greater than 2.2 micro metres?

Answer 36

there will be either no thin filaments that myosin heads will binds to, or decrease of binding to actin thus overall, force generated is reduced