Structure and Function of Skeletal muscle

Question 1

skeletal muscle functions?

Answer 1

move body
control body posture
support and protect
control orifices (voluntary control)
participate in temp regulation
generate peristaltic movement

Question 2

muscle fibre is enveloped by?

Answer 2

by a sheath of connective tissue

Question 3

bundle of muscle fibres are enveloped by?

Answer 3

by a sheath of connective tissue

Question 4

muscle is enveloped by ?

Answer 4

sheath of connective tissue

Question 5

myofibrils are made up of what?

Answer 5

made up of myofilaments

Question 6

what myofilaments are myofibrils made up from?

Answer 6

actin and myosin

Question 7

smallest unit in a myofibril is?

Answer 7

a sarcomere, these are highly aligned

Question 8

myosin filaments are made up of what?

Answer 8

several myosin molecules

Question 9

where are myosin filaments located?

Answer 9

they are centred between z-discs and m-lines by Titin (protein that holds them in place)

Question 10

actin molecules are attached to what protein? allowing?

Answer 10

nebulin, only present in skeletal muscle
ensuring uniformity in length

Question 11

nebulin?

Answer 11

protein only present in skeletal muscle

Question 12

T tubules?

Answer 12

transverse tubules
folds within muscle cell membrane
quick conduction of signals onto muscle cells to allow for quick response
correlated with z discs/run through fibres either side of the z-discs
close contact w/ sarcoplasmic reticulum
rapid conduction of action potentials

Question 13

neuromuscular junction - NMJ?

Answer 13

where nerve cell terminates onto muscle fibre

Question 14

NMJ?

Answer 14

post synaptic membrane is folded - more receptors so can pick up more of signalling molecule - Ach

Question 15

when potential arrives at NMJ?

Answer 15

action potential arises on post synaptic side of membrane

Question 16

when action potential arrives at pre synaptic membrane?

Answer 16

calcium influx due to voltage gated ca channels opening
ach released into synapse
bind to receptors
ion channels open mainly Na
depolarises membrane potential
more positive
forms excitatory post synaptic potential
opening of Na channels further along so ap (action potential) can propagate/move across the whole cell so muscle can start contracting
can only last as long as the ach is binded to receptors

Question 17

muscle contractions - what causes sliding?

Answer 17

sliding filament mechanism - by binding the myosin heads to actin, followed by bending of the heads towards the sarcomere

Question 18

muscle contraction - myosin and actin binding to each other?

Answer 18

form a cross bridge
myosin heads have an ATP binding site which hydrolyses ATP
this releases energy which is stored by myosin heads
calcium is released from sarcoplasmic reticulum allows heads to bind and bend = power stroke
when ADP is released following power stroke myosin heads bind to another ATP molecule, breaking the myosin/actin bond (breaks cross bridge)

Question 19

what controls the muscle contractions?

Answer 19

tropomyosin and troponin
these prevent binding of myosin to actin in resting muscles

Question 20

when tropomyosin binds?

Answer 20

myosin binding site becomes uncovered as troponin moves - so can bind to actin

Question 21

slide 14, week 2 sem 2
summary of everything

Question 22

ion pumps function>

Answer 22

get all calcium back into sarcoplasmic reticulum and can dissociate from troponin so tropomyosin returns to blocking the myosin binding site so muscle can relax

Question 23

What happens during Rigor mortis?

Answer 23

ATP production ceases
ATP-dependent ion pumps in cells stop functioning
Ca levels no longer maintained
Ca leaks into cytosol
Within a few hours of death, Ca levels are high enough to causes binding of myosin heads
Low ATP means these bonds do not break
enzymes can then break muscle tissue down - this is what happens when you can come out of rigor mortis

Question 24

hypocalcaemia in ruminants?

Answer 24

paresis (muscle paralysis)

Question 25

hypocalcaemia in dogs?

Answer 25

tetany (muscle twitching)

Question 26

what does calcium regulate?

Answer 26

regulates the release of Ach in the synapse between the motor neurone and the muscle cell

Question 27

in cows, no calcium?

Answer 27

means no transmission of signals across NMJ

Question 28

in dogs, no calcium?

Answer 28

amount of ACH produced normally is higher so transmission can still occur, only twitching not paralysis

Question 29

spontaneous action potential generation?

Answer 29

low extracellular calcium depolarises all cells, in neurones this is what the result is

Question 30

in dogs - hypocslcaemia?

Answer 30

involuntary contractions occur

Question 31

in cows - hypocalcaemia?

Answer 31

this increased firing frequency of APs due to low extracellular Ca depolarising all cells does not lead to increased muscular activity as the NMJ is blocked

Question 32

some of ATP produced by muscle fibres is used for what?

Answer 32

used to make creatine phosphate

Question 33

reaction for the formation of creatine phosphate?

Answer 33

ATP + Creatine → ADP + Creatine Phosphate

Question 34

What is ATP + Creatine → ADP + Creatine Phosphate catalysed by?

Answer 34

creatine kinase

Question 35

main energy substrate?

Answer 35

glucose from glycogen stores leads to glycolysis if not glycogen stores then use oxidative phosphorylation to get glucose

Question 36

ATP is essential for what during muscle contraction?

Answer 36

energy for power stroke of the cross-bridge ATP must bind to myosin heads to break cross bridge Energy released by hydrolysis of ATP is necessary for pumping calcium back into sarcoplasmic reticulum

Question 37

location of smooth muscle?

Answer 37

attached to bones

Question 38

location of smooth muscle?

Answer 38

walls of hollow organs, blood vessels, eyes, glands, skin

Question 39

location of cardiac muscle?

Answer 39

heart

Question 40

functions of skeletal muscle?

Answer 40

body movements

Question 41

functions of smooth muscle?

Answer 41

transport of food through the digestive tract, emptying of the urinary bladder, regulation of blood vessel diameter etc.

Question 42

function of cardiac muscle?

Answer 42

pumping of blood

Question 43

what is the calcium binding protein for skeletal muscle?

Answer 43

troponin

Question 44

what is the calcium binding protein for smooth muscle?

Answer 44

calmodulin

Question 45

what is the calcium binding protein for cardiac muscle?

Answer 45

troponin

Question 46

Does skeletal muscle have voluntary control?

Answer 46

yes

Question 47

Does smooth muscle have voluntary control?

Answer 47

No

Question 48

Does cardiac muscle have voluntary control?

Answer 48

No

Question 49

How do cells of skeletal muscle communicate?

Answer 49

via NMJ neuromuscular junction

Question 50

How do cells of smooth muscle communicate?

Answer 50

tight junctions

Question 51

How do cells of cardiac muscle communicate?

Answer 51

Via gap junctions

Question 52

What determines the direction of the reaction between ATP + Creatine in order to form ADP + Creatine Phosphate

Answer 52

concentrations of ATP and ADP

Question 53

In resting muscles, describe the concentration of creatine phosphate compared to that of ATP:

Answer 53

Creatine phosphate concentration is much higher than ATP

Question 54

As soon as muscular contractions start, what happens to ATP concentration?

Answer 54

it decreases