MUSCLES

Question 1

ANTAGONISTIC PAIR

Answer 1

muscles acts in antagonistic pairs against an incompressible skeleton.

Question 2

sarcolemma

Answer 2

the cell membrane of the muscle fiber cells is called the sarcolemma.

Question 3

transverse tubules

Answer 3

sarcolemma folding inwards and sticking to the sarcoplasm is called transverse tubules,
- helps to spread electrical impulses throughout the sarcoplasm.

Question 4

sarcoplasmic reticulum

Answer 4

stores and releases calcium ions needed for muscle contraction.

Question 5

myofibrils

Answer 5

long, cylindrical organelles in the muscle fibres which are made up of proteins and are highly specialised for muscle contraction.

Question 6

proteins in myofibrils

Answer 6

actin( thin filaments) and myosin ( thick filaments) that makes up the sacromere.

Question 7

dark bands

Answer 7

dark bands contain thick myosin filaments overlapped by some actin filaments - these are called the A bands.

Question 8

i bands

Answer 8

the light bands contain only thin actin filaments which is called the i band.

Question 9

sacromeres

Answer 9

a myofibril is made up of many short units called sacromere.

Question 10

z line

Answer 10

ends of sacromere are marked with a z line.

Question 11

m line

Answer 11

m line is the middle of the myosin filaments.

Question 12

h zone

Answer 12

h zone only contains myosin filaments.

Question 13

sliding filament theory

Answer 13

myosin and actin filaments slide over each other to make the sacromere contract - the myofilaments dont contract themselves - the sacromeres get shorter when muslces are contracted.

Question 14

myosin filaments and globular heads

Answer 14

• myosin filaments have globular heads.
• each myosin head has a binding site for ATP and actin.
• actin filament have binding sites for myosin heads called the actin myosin cross bridge.
• a protein called tropomyosin is found between actin filaments which helps myofilaments move past each other.

Question 15

tropomyosin

Answer 15

when muscles are relaxing, the actin - myosin binding site is blocked by tropomyosin so thr myofilaments canmnot slide past each other.

Question 16

muscle contraction and influx of calcium ions

Answer 16

• when an action potential from a motor neuron stimulates a muscle cell, it depolarises the sarcolemma and depolaridation spreads down the t - tubules to the sarcoplasmic reticulum.
• which causes the sarcoplasmic reticulum to release the stored calcium ions into the sarcoplasm.
• calcium ions binds to a protein attatched to tropomyosin causing it to change its shape which pulls tropomyosin out of the actin myosin binding sites.
• now the binding sites are exposed and the myosin head can now bind to actin. the bond formed when a myosin head binds to the actin filament is called the actin myosin cross bridge.

Question 17

muscle contraction and atp and calcium ions ( more )

Answer 17

• ca+2 ions also activates the enzyme atp hydrolase which hydrolyses the enzyme atp into adp and pi providing the energy needed for muscle contraction.
• the energy relesed causes myosin head to bend which pulls the actin filament in a rowing action.
• another atp molecule provides energy to break the actin myosin cross bridge so the myosin head detatches from the actin filament.
• the myosin head then reatttaches to a different binding site and a new cross bridge is formed and the cycle is repeated .
• sacromeres are shortened causing the muscles to contract. the cycle continues as long as there is the presence of calcium ions.

Question 18

calcium ions and muscle relaxation

Answer 18

when muscles are not stimulated, calcium ions leave their binding sites and are moved by active transport back to the sarcoplasmic reticulum which also requires atp.
- tropomyoisn molecules moves back blocking the actin myosin binding site.
- no muscle contraction as there is no binding between myosin head and actin filaments.
- actin filaments slides back to its original position and the sacromere lengthens.

Question 19

what provides the energy for muscle contraction

Answer 19

atp and phosphocreatine

Question 20

3 ways in which atp is generated

Answer 20

• aerobic respiration, anaerobic respiration and atp phosphocreatine system.