specialised tissues

Question 1

function of skeletal muscle

Answer 1

connect bones and allow movement

Question 2

name both muscles within an antagonistic pair

Answer 2

flexor and extender

Question 3

define isotonic contraction

Answer 3

muscle length changes, tension remains the same

Question 4

define isometric contraction

Answer 4

muscle length remains the same, tension changes

Question 5

whate are myofibres and what do they do

Answer 5

cylindrical, multinucleated bundle of cells packed with myofibrils which extend length

Question 6

why is skeletal muscle striated

Answer 6

divided into alternating dark and light bands

Question 7

A-band

Answer 7

dark bands interesected by darker region (H-zone)

Question 8

I-band

Answer 8

light bands intersected by dark line (Z-line)

Question 9

Z-line

Answer 9

made up of a-actin and CapZ; defines lateral boundaries of sarcomere

Question 10

define sarcomere

Answer 10

functional unit of muscle lying between two Z-lines

Question 11

what does desmin do

Answer 11

links Z-lines of adjacent myofibrils

Question 12

actin

Answer 12

polymeric thin filament of two twisted a-helices; displays polarity

Question 13

myosin

Answer 13

thick filaments (motor proteins); contain numerous globular heads that interact with actin

Question 14

titin

Answer 14

very large spring-like filaments anchoring myosin to Z-line; associated with thick and thin filaments in relaxed muscle

Question 15

nebulin

Answer 15

large filaments associated with actin

Question 16

CapZ and tropomodulin

Answer 16

associated with +ve (nearest Z-line) and -ve (furtherst Z-line) ends of actin respectively

Question 17

sarcomere diagram

Answer 17

diagram from tissues 7

Question 18

T-tubules

Answer 18

membrane invaginations into EC fluid

Question 19

sarcoplasmic reticulum

Answer 19

stores of IC Ca2+

Question 20

skeletal muscle excitation-contraction coupling

Answer 20

action potential propagates along sarcolemma and down T-tubules → depolarisation activates dihyropiridine receptors (DHPR) → conformational change → ryanodine receptors (RyR) on SR open → Ca2+ released

Question 21

isotonic contraction: tension and force

Answer 21

tension is greater than force exerted by load so Z-lines become closer

Question 22

isotonic contraction: sliding filament theory

Answer 22

Ca2+ binding to troponin causes movement of troponin from tropomyosin chain → exposes myosin binding sites on actin chain → charged myosin heads bind to exposed site on actin filament → binding and discharge of ATP causes myosin head to pivot (power stroke) → actin filament pulled towards sarcomere centre → ATP binds → releases myosin head from actin chain → ATP hydrolysed → energy to recharge myosin head

Question 23

isometric contraction: tention and force

Answer 23

tension is equal to force exerted by load so muscle doesn’t shorten

Question 24

isometric contraction: sliding filament theory

Answer 24

myosin heads attach at same point as actin pulled in and out; ATP still required to charge heads

Question 25

define motor unit

Answer 25

single motor neurone all ats its muscle fibres

Question 26

define recruitment

Answer 26

increasing number of “active” motor units

Question 27

what does increasing recruitment cause

Answer 27

increase in force

Question 28

what effect does increasing speed of filament sliding have on number of cross-bridges

Answer 28

fewer cross-bridges