L11

Question 1

What are the 3 types of muscles?. briefly describe each.

Answer 1

skeletal : striated , moves voluntarily , each skeletal muscle is supple with its own nerves , vein and artery . there are 640 skeletal muscles in the body

cardiac :also striated , is involuntary , found in the heart

smooth muscle : not striated , found in visceral organs where movement is involuntary .

Question 2

what is the electrically excitable plasma membrane that surrounds individual muscle fibers ?

Answer 2

sarcolemma

Question 3

what are myofibrils?

Answer 3

unit arranged in parallel . they are embedded in intracellular fluid .forms muscle fibers

Question 4

what is the intracellular fluid that myofibrils are embedded in called?

Answer 4

sarcoplasm

Question 5

what is the functional unit of the muscle called?

Answer 5

sarcomere

Question 6

what is the sarcoplasmatic reticulum?

Answer 6

the muscle cells own version of endoplasmic reticulum , it is the cells transport and storage system . it’s walls are loaded with calcium pumps which use ATP to save up calcium ions

also studded with calcium channels that are linked to protein in the membrane of the muscle cell

Question 7

what does the sarcoplasmic reticulum surround ?

Answer 7

The sarcoplasmic reticulum with its transverse (T) tubules and terminal cisterns surrounds each myofibril. The T tubules invaginate from the sarcolemma.

Question 8

describe what is seen under the electron microscope when veiwing the myofibril.

Answer 8

alternating dark and light bands can be seen. these bands are referred to as I and A bands.

Question 9

what are A and I bands of the myofibril?

Answer 9

A bands are dark bands while I bands are light bands

Question 10

what part of the A band is least dense ?

Answer 10

– central region of the A band ( the H zone ) appears less dense than the rest of the band

Question 11

which band Is bisected by the z line?

Answer 11

I band

Question 12

where do thin filaments exist ?

Answer 12

In the I band , it also exists in parts of the A band but not the H zone

Question 13

what proteins do thin filaments contain ?

Answer 13

actin , tropomyosin , and troponin

Question 14

how is the thin filament arranged ?

Answer 14

around the thick filament as a hexagonal array

Question 15

where are the thick bands present?

Answer 15

in the A bands

Question 16

what protein does the thick fillaments have ?

Answer 16

myosin

Question 17

how are thick filaments arranged ?

Answer 17

cross section as a hexagonal array

Question 18

what is G-actin?

Answer 18

monomeric actin that is globular and makes 25% of muscle protein by weight

Question 19

what does G-actin do in presence of Mg2+?

Answer 19

polymerizes to form an insoluable double helical fillament called F actin

Question 20

what is myosin ?

Answer 20

constitue a family of proteins

contributes 55% to muscle protein by weight and it forms thick filaments

Question 21

describe the structure of myosin .

Answer 21

has fibrous tail consisting of 2 intertwined helices

each helix has a globular head portion at one end

Question 22

what are the chains that myosin consists of?

Answer 22

2 heavy chains (H chains ) and 4 light chains (L chains )

Question 23

what so tropomyosin and troponin do?

Answer 23

complex present in thin filaments that block myosin from attaching to actin , this blockage is removed when it is bonded with calcium

Question 24

what is tropomyosin?

Answer 24

fibrous molecule that consists of two chains , alpha and beta , that attach to f actin in the groove between the filaments

it is present in all muscular and muscle like structure

Question 25

describe the troponin complex .

Answer 25

unique to strained muscles and consists of three polypeptides .

Question 26

what are the three polypeptides that troponin consists of?

Answer 26

TpT: Binds to tropomyosin as well as other 2 troponin components TpI: inhibits F actin- myosin interaction and also binds to other components of troponin TpC:calcium binding polypeptide . 4 molecules of calcium ion are bound per molecule of troponin C

Question 27

When highly sensitive assays are used, cardiac-specific isoforms both troponin I and troponin T are detectable in serum as early as 2 hours after Acute Myocardial Infarction. Levels reach their peak at 12 hours and remain elevated for 7 to 10 days. Troponin can therefore be used even for patients with delayed presentations.

Answer 27

0-0

Question 28

list the sequence of events in contraction.(study fromCB yabn el 7alal)

Answer 28

discharge of motor neuron and release of acetylcholine binding of acetylcholine to nicotinic acetylcholine receptors generation of action potential in muscle fibers release of Ca2+ from terminal cisterns of sarcoplasmic reticulum and diffusion to thick and thin filaments binding of ca 2+ to troponin C , uncovering myosin binding sites of actin formation of cross linkages between actin and myosin and sliding of thin on thick filaments producing shortening

Question 29

steps of relaxation : | CB yabni

Answer 29

Ca2+ pumped back into sarcoplasmic reticulum Release of Ca2+ from troponin Cessation of interaction between actin and myosin

Question 30

what is malignant hyperthermia ?

Answer 30

body temp rises when exposed to certain drugs reaction consists primarily of rigidity of skeletal muscles , hyper metabolism and high fever

Question 31

why does mutation in calcium channel protein (RYR1) cause high cytosolic concentration of CA2+ in skeletal muscle ?

Answer 31

when a mutation on the RYR1 gene occurs the mutated channel opens up more easily and stays open for longer , flooding the cytosol with cA2+

Question 32

What does high levels of ca2+ stimulate ?

Answer 32

sustained muscle contraction (rigidity ). it also stimulates breakdown of glycogen , glycosides and eorobic metabolism( resulting in excessive production of heat)

Question 33

what is dystrophin and what is its function?

Answer 33

it is a cytoskeleton protein that connects F-actin to dystroglycan complex

Question 34

what is a dystrophin complex ?

Answer 34

The dystrophin complex acts as an anchor, connecting each muscle cell's cytoskeleton with the framework of extracellular matrix proteins. Also play a role in cell signalling by interacting with chemical signals. absence of dystrophin, plasma membrane of muscle cells gets damaged during contractile process leading to muscle cell death.

Question 35

what diseases is the term muscle dystrophy applied too ?

Answer 35

The term muscular dystrophy is applied to diseases that cause progressive weakness of skeletal muscle.

Question 36

what is Duchenne muscular dystrophy

Answer 36

a serious form of dystrophy in which the dystrophin protein is absent from muscle. It is X-linked

Question 37

what is beer muscular dystrophy ?

Answer 37

Dystrophin is present but altered or reduced in amount.

Question 38

what is sarcopenia ?

Answer 38

Loss of skeletal muscle mass with age Mainly after 5th decade of life Can lead to frailty and loss of functional capacity Regular exercise during middle age reduces sarcopenia