Muscles

Question 1

What are muscles

Answer 1

Specialised effectors that bring about movement through muscle contraction

Question 2

Explain the structure of muscles

Answer 2

-consist of many muscle fibres branched together
-each fibre- surrounded by a sarcolemma
-each fibre- multinucleate-nuclei inside sarcolemma
-fibre- specialised cell- contains cell organelles typically found in any cell- particularly rich in mitochondria
-at intervals, sarcolemma folds deeply inwards- transverse tubules
-bulk of muscle fibre, filled with highly specialised contractile units

Question 3

Name the two types of protein that make up a myofibril

Answer 3

-myosin
-actin

Question 4

What is the m-line

Answer 4

thin disc that links myosin- runs perpendicular to the orientation of the myosin filaments

Question 5

What is the z-line

Answer 5

actin filaments slot between outer edges

Question 6

What is the sarcomere

Answer 6

-a section of myofibril between two z-lines

Question 7

what is the a-band

Answer 7

areas where thinner actin penetrates between myosin filaments

Question 8

What is I-band

Answer 8

areas that contain only actin

Question 9

What is the h-zone

Answer 9

centre of the a-band- contains just myosin

Question 10

Explain muscle contraction

Answer 10

1. An action potential stimulates the muscle fibre as it travels through its extensive system of t-tubules.
2. The action poteitnal causes the calium ion channels in the sarcoplasmic reticulum to open
3. This causes the calcium ions that have been stored in the sarcoplasmic reticulum to diffuse into the sarcoplasm, down a concentration.
4. Calcium ions cause the ancillary protein tropomyosin, which normally covers the binding sites of the actin filaments to be moved, enabling the myosin bulbous heads to link with the actin binding sites- forming actomyosin bridges
5. Once attached, the myosin heads change angle- rock back 45 degrees- pulling the actin filaments over the adjacent myosin filaments
6. An ATP molecule attaches to each myosin head, and the energy released from its hydrolysis, enables the myosin heads to detach from the stationary actin binding site, and return to its original position.
7. The detached myosin head repeats the process, of attachment, rotation and release, around 5 times every second
8. The cycle continues as long as the muscle fibre receives nervous stimulation and calcium ions are present.

Question 11

What changes occur in the myofibril when contracted

Answer 11

-Sarcomere shortens
-h zone becomes shorter
-i band becomes shorter
-a band remains the same length