Organisms Response to Change - Skeletal Muscles

Question 1

what is the function of skeletal muscles?

Answer 1

voluntary movements

Question 2

what is the structure of a skeletal muscle?

Answer 2

consists of bundles of muscle fibres

Question 3

what is the structure of muscle fibres?

Answer 3

formed from many cells fused together

Question 4

what is a sarcolemma?

Answer 4

the cell membrane of a muscle fibre

Question 5

what is a sarcoplasm?

Answer 5

the cytoplasm of a muscle fibre

Question 6

what is a sarcoplasmic reticulum?

Answer 6

the endoplasmic reticulum of a muscle fibre

Question 7

why do muscle fibres have a banded appearance?

Answer 7

myofibrils

Question 8

what are myofibrils made up of?

Answer 8

protein filaments, which consist of thin and thick myofilaments

Question 9

what is actin?

Answer 9

thin myofilaments

Question 10

what is myosin?

Answer 10

thick myofilaments

Question 11

what does tropomyosin form?

Answer 11

long thin threads that are wound around actin filaments

Question 12

what is a sarcomere?

Answer 12

a section of a muscle fibre, specifically the distance between one Z disc to the next

Question 13

what is the Z disc?

Answer 13

the section of the sarcomere that actin is attached to

Question 14

what is the A band?

Answer 14

section of the sarcomere where myosin and actin is found

Question 15

what is the I band?

Answer 15

section of the sarcomere containing only actin

Question 16

what is the M line?

Answer 16

where myosin is attached

Question 17

what is the H band?

Answer 17

section of the sarcomere containing only myosin

Question 18

what happens to a sarcomere when the muscle contracts?

Answer 18

it gets shorter because the I band slides into the H band

Question 19

what happens to the length of the A, I and H bands during muscle contraction?

Answer 19

A band - stays same

I band - shorter

H band - shorter

Question 20

what does the motor unit do?

Answer 20

supplies all the muscle fibres from a single motor neuron

Question 21

what is released when the action potential reaches the end of a motor neurone?

Answer 21

acetylcholine

Question 22

are neuromuscular junctions excitatory or inhibitory?

Answer 22

excitatory only

Question 23

what is a neuromuscular junction?

Answer 23

point where a motor joint meets a skeletal muscle fibre

Question 24

what are t-tubules?

Answer 24

extensions of the cell surface membrane

Question 25

what is the function of t-tubules?

Answer 25

carry the wave of excitation to the sarcoplasmic reticulum

Question 26

when the wave of excitation reaches the sarcoplasmic reticulum, what occurs?

Answer 26

Calcium ions are activated in the sarcoplasmic reticulum, which then diffuse into the sarcoplasm

Question 27

what are the similarities between neuromuscular junctions and cholinergic synapses?

Answer 27

neurotransmitters transported by diffusion

receptors cause influx of sodium ions

use a sodium potassium pump to repolarise axons

use enzymes to break down neurotransmitters

Question 28

what are the differences between neuromuscular junctions and cholinergic synapses?

Answer 28

neuromuscular only excitatory, cholinergic can be inhibitory too

neuromuscular links neurons to muscles only, cholinergic also links neurons to other organs/effectors

action potential ends at neuromuscular, cholinergic may produce a new one

acetylcholine binds to receptors on muscle fiber in neuromuscular, binds to receptors on membrane of post-synaptic neuron in cholinergic

Question 29

describe the sliding filament theory of muscle contraction

Answer 29

calcium ions cause tropomyosin to move away from actin binding sites, allowing a myosin head to attach and form a cross bridge

myosin head changes angle, pulling actin filament along and releasing ADP

ATP attaches to myosin head, allowing it to detach

ATP hydrolysed allowing myosin head to return to original position

Question 30

what is myosin made up of?

Answer 30

fibrous protein

globular protein

Question 31

what is the structure of the fibrous protein in myosin?

Answer 31

protein arranged into a tail-shaped filament

Question 32

what is the structure of the globular protein in myosin?

Answer 32

two bulbous structures at the end of the protein

Question 33

how is muscle contraction stimulated?

Answer 33

action potential reaches neuromuscular junctions, causing calcium ions to diffuse into the synaptic knob

this causes synaptic vesicles to fuse with the presynaptic membrane and release acetylcholine, which diffuses across

acetylcholine binds to receptors of muscle cell membrane, causing it to depolarise

Question 34

what type of exercise are slow twitch muscle fibres adapted for?

Answer 34

endurance over a long period of time

Question 35

what are the adaptations of slow twitch muscle fibres?

Answer 35

contracts slowly and less powerfully

lots of mitochondria for aerobic respiration

rich supply of blood vessels and myoglobin

Question 36

what is myoglobin?

Answer 36

red molecule that stores oxygen for respiration

Question 37

what type of exercise are fast twitch muscle fibres adapted for?

Answer 37

short and intensive exercise

Question 38

what are the adaptations of fast twitch muscle fibres?

Answer 38

contract rapidly and powerfully

lots of thick myosin filaments

high conc of glycogen as well as enzymes needed for anaerobic respiration

stores of phosphocreatine

Question 39

what is phosphocreatine?

Answer 39

a molecule that can rapidly produce ADP in anaerobic conditions by donating a phosphate group