Muscles

Question 1

A band

Answer 1

Length of myosin
-Never changes length

Question 2

H zone

Answer 2

Just myosin no actin
-H zones decreases when muscle contract

Question 3

I band

Answer 3

Just actin
-Relaxed muscle has a big I band
-Contracted muscles have a smaller I band

Question 4

Z lines

Answer 4

Start and end of one sarcomere

Question 5

Why are muscles so strong

Answer 5

-Each muscle is made up of tiny fibres called myofibrils
-These fibres are bundled up

Question 6

Myofibrils are made of

Answer 6

-Actin: a thin filament consisting of 2 strands wrapped around each other
-Myosin: thicker, consists of long rod shaped fibres with bulbous heads that project to the side

Question 7

How a muscle contracts

Answer 7

1. Calcium ions diffuse into myofibrils from the sarcoplasmic reticulum
2. Calcium ions cause movement of tropomyosin
3. This movement causes exposure of the myosin binding sites on the actin
4. Myosin heads attach to the binding site on the actin, forming cross-bridges between the two filaments
5. This causes myosin heads to bend, pulling actin towards the centre of the sarcomere
6. Attachment of a new ATP to the myosin head causes the myosin head to detach from actin
7. Hydrolysis of ATP re-cocks myosin heads so myosin heads can reattach to a binding site further along the actin (processes repeats)