muscles

Question 1

types of muscle

Answer 1

• skeletal
• cardiac
• involuntary

Question 2

skeletal muscle

Answer 2

• make up bulk of body muscle tissue
• responsible for movement
• striated
• regularly arranged so muscle contracts in 1 direction
• rapid contraction speed
• short length of contraction
• fibres are tubular and multinucleated

Question 3

cardiac muscle

Answer 3

• only found in heart
• myogenic- contract without the need for nervous stimulus causing heart to beat regular rhythm
• specialised striated- much fainter than in skeletal muscle
• cells branch and interconnect resulting in simultaneous contraction
• intermediate contraction speed
• intermediate length of contraction
• fibres are branched and uninucleated

Question 4

involuntary muscle

Answer 4

• smooth muscle
• e.g. walls of stomach, bladder, blood vessels, digestive tract where they move food along gut through peristalsis
• non striated
• no regular arrangement- different cells contract in different directions
• slow contraction speed
• can remain contracted for relatively long time
• fibres are spindle shaped and uninucleated

Question 5

what are skeletal muscles made of

Answer 5

• bundles of muscle fibres

Question 6

sarcolemma

Answer 6

plasma membrane of muscle fibres

Question 7

sarcoplasm

Answer 7

shared cytoplasm within a muscle fibre

Question 8

nuclei in muscle fibres

Answer 8

• longer than in normal cells
• as they are formed by many individual embryonic muscle cells fusing together
• so makes muscle stronger, as junction between adjacent cells would act as point of weakness

Question 9

transverse/T tubules

Answer 9

• parts of the sarcolemma which fold inwards
• helps spread electrical impulses throughout the sarcoplasm
• ensures whole of the fibre receives impulse to contract at the same time

Question 10

what do muscle fibres have lots of

Answer 10

mitochondria to provide ATP needed for muscle contraction

Question 11

sarcoplasmic reticulum

Answer 11

• extends throughout the muscle fibre
• contains calcium ions required for muscle contraction

Question 12

myofibrils

Answer 12

• each muscle fibre contains them
• long cylindrical organelles made of protein
• specialised for contraction
• provide no force on their own but collectively powerful
• lined up in parallel to provide maximum force when all contract together

Question 13

what protein filaments are myofibrils made of

Answer 13

• actin
• myosin

Question 14

actin

Answer 14

thinner filament consists of 2 strands twisted around each other

Question 15

myosin

Answer 15

thicker filament consists of long rod-shaped fibres with bulbous heads that project to one side

Question 16

light bands in myofibrils

Answer 16

• areas appear light as actin and myosin dont overlap
• I bands

Question 17

dark bands in myofibrils

Answer 17

• appear dark because of presence of thick myosin filaments
• edges are particularly dark as myosin overlaps with actin
• A bands

Question 18

Z line

Answer 18

• found in centre of each light band
• distance between adjacent Z lines is a sarcomere

Question 19

sarcomere

Answer 19

• functional unit of myofibril
• when muscle contracts, sarcomere shortens

Question 20

H zone

Answer 20

• lighter region in centre of each dark band
• only myosin filaments present

Question 21

sliding filament model

Answer 21

muscle contraction where actin and myosin filaments slide past each other

Question 22

what happens to a sarcomere during contraction

Answer 22

• myosin filaments pull actin filaments inwards towards centre of sarcomere
• light bands shorten
• sarcomere shortens
• H zone shortens
• dark bands stay the same

Question 23

structure of myosin

Answer 23

• globular hinged heads to allow them to move back and forth
• on head is binding site for actin and ATP
• tails of several hundred myosin molecules align together to form myosin filament

Question 24

structure of actin in relation to myosin

Answer 24

• actin filaments have actin-myosin binding site for myosin heads
• when relaxed, they are blocked by tropomyosin protein which is held in place by troponin
• so myosin heads cant bind to actin so filaments can slide past each other

Question 25

why are there many neuromuscular junctions along muscle

Answer 25

- to ensure all the muscle fibres contract simultaneously - if only 1 existed, muscle fibres would not contract together therefore contraction of the muscle would not be as powerful - it would be much slower, as wave of contraction would have to travel across the muscle to stimulate the individual fibres to contract

Question 26

motor unit

Answer 26

- all muscle fibres supplied by a single motor neurone - if strong force is needed then large number of motor units are stimulated

Question 27

what happens after depolarisation of sarcolemma

Answer 27

- travels into muscle fibre through T tubules - contact with sarcoplasmic reticulum which contains stored calcium ions actively absorbed from sarcoplasm - when action potential reaches sarcoplasmic reticulum it stimulates calcium ion channels to open and calcium ions diffuse down conc gradient into sarcoplasm - calcium ions bind to troponin causing change in shape - pulls tropomyosin moving it away from actin myosin binding site on actin filament - myosin head exposed to actin binds to it forming cross bridge - myosin head flexes which pulls actin filament along and ADP is released from myosin head - ATP binds to myosin head which causes head to detach from actin filament - calcium ions in sarcoplasm activate ATPase activity of myosin - this hydrolyses ATP to ADP and phosphate releasing energy which myosin head uses to return to og position - cycle is repeated and continues as long as muscle remains stimulated

Question 28

M line

Answer 28

the middle of a sarcomere- middle dark line of the H zone