skeletal muscle 3.6

Question 1

name the three types of muscle in the body and where they are located

Answer 1

cardiac: exclusively found in the heart
smooth: walls of blood vessels and intestines
skeletal: attached to incompressible skeleton by tendons

Question 2

what is an antagonistic pair of muscles

Answer 2

muscles can only pull
so they work in pairs to move bones around joints
pairs pull in opposite directions

Question 3

what is the structure of skeletal muscle

Answer 3

muscle cells are fused together to form bundles of parallel muscle fibres (myofibrils)

Question 4

myofibrils

Answer 4

site of contraction

Question 5

sarcoplasm

Answer 5

shared nuclei and cytoplasm
lots of mitochondria and endoplasmic reticulum

Question 6

sarcolemma

Answer 6

fold inwards towards sarcoplasm
to form transverse tubules

Question 7

what is the Z line

Answer 7

boundary between sarcomeres

Question 8

what is the I band

Answer 8

only actin

Question 9

what is the A band

Answer 9

overlap of actin and myosin

Question 10

what is the H zone

Answer 10

only myosin

Question 11

which band is light

Answer 11

I band (only actin)

Question 12

what band is dark

Answer 12

A band (actin and myosin)

Question 13

how is muscle contraction stimulated

Answer 13

action potential at neuromuscular junction
voltage-gated Ca2+ channels open
vesicles move towards and fuse with presynaptic membrane
exocytosis of acetylcholine
diffuses across synaptic cleft
acetylcholine binds to receptors on Na+ channel proteins on skeletal muscle cell membrane
influx of Na+ = depolarisation

Question 14

explain role of Ca2+ ions in muscle contraction

Answer 14

action potentials move through T-tubules in the sarcoplasm
Ca2+ channels in sarcoplasmic reticulum open
Ca2+ binds to troponin
triggers change in tropomyosin
exposes binding sites on actin filaments
so actinomyosin bridges can form

Question 15

what is the sliding filament theory

Answer 15

myosin head with ADP attached forms cross bridge with actin
myosin head changes shape and loses ADP
pulls actin over myosin
ATP attaches to myosin head
causes it to detach from actin
ATPase hydrolyses ATP so myosin head can return to original position
myosin head reattaches to actin further along filament

Question 16

what does ATPase hydrolyse ATP to

Answer 16

ADP and Pi

Question 17

how does sliding filament action cause a myofibril to shorten

Answer 17

myosin heads flex in opposite directions
actin filaments are pulled towards each other
distance between adjacent Z lines shortens

Question 18

state 4 pieces of evidence that support the sliding filament theory

Answer 18

H zone narrows
I band narrows
Z lines get closer
A zone remains the same width

Question 19

what does Z lines getting closer show

Answer 19

the sarcomere shortens

Question 20

what does the A zone remaining the same width prove

Answer 20

myosin filaments do not shorten

Question 21

what happens during muscle relaxation

Answer 21

Ca2+ is actively transported back into endoplasmic reticulum
tropomyosin once again blocks actin binding sites
myosin cannot bind
antagonistic muscles can pull actin filaments out from between myosin

Question 22

explain the role of phosphocreatine in muscle contraction

Answer 22

phosphorylates ADP directly to ATP when oxygen for aerobic respiration is limited

Question 23

how could a student calculate the length of one sarcomere

Answer 23

view thin slice of muscle under optical microscope
calibrate eyepiece graticule
measure distance from middle of one light band to middle of another

Question 24

where are slow twitch muscle fibres found in the body

Answer 24

sites of sustained contraction eg calf muscle

Question 25

where are fast twitch muscle fibres found in the body

Answer 25

sites of short term, rapid, powerful contraction eg biceps

Question 26

what is the role of slow twitch muscle fibres

Answer 26

long duration contraction well-adapted to aerobic respiration to prevent lactate buildup

Question 27

what is the role of fast twitch muscle fibres

Answer 27

powerful short term contraction well adapted to anaerobic respiration

Question 28

explain the structure and properties of slow-twitch muscle fibres (4)

Answer 28

glycogen store - many terminal ends can be hydrolysed to release glucose for respiration contain myoglobin - higher affinity for oxygen than haemoglobin at lower partial pressures many mitochondria - aerobic respiration produces more ATP surrounded by many blood vessels - high supply of oxygen and glucose

Question 29

explain the structure and properties of fast twitch muscle fibres (5)

Answer 29

large store of phosphocreatine more myosin filaments thicker myosin filaments high concentration of enzymes involved in anaerobic respiration extensive sarcoplasmic reticulum - rapid uptake and release of Ca2+

Question 30

what is a motor unit

Answer 30

one motor neuron supplies several muscle fibres which act simultaneously as one functional unit