Muscles

Question 1

Describe how muscles work

Answer 1

Work in antagonistic pairs and pull in opposite directions e.g. biceps / triceps. One muscle contracts, pulling on bone, producing force
and one muscle relaxes

Question 2

Describe the gross and microscopic structure of skeletal muscle

Answer 2

Made of many bundles of muscle fibres packaged together, attached to bones by tendons. Muscle fibres contain:
* Sarcolemma (cell membrane) which folds inwards
(invagination) to form transverse (T) tubules
* Sarcoplasm (cytoplasm)
* Multiple nuclei
* Many myofibrils
* Sarcoplasmic reticulum (endoplasmic reticulum)
* Many mitochondria

Question 3

Describe the ultrastructure of a myofibril

Answer 3

Made of two types of long protein filaments, arranged in parallel
* Myosin - thick filament
* Actin - thin filament
They are arranged in functional units called sarcomeres. The ends form the Z-line, and the middle forms the M-line. The H zone contains only myosin

Question 4

Draw and label a sarcomere

Answer 4

https://images.squarespace-cdn.com/content/v1/5c5aed8434c4e20e953d6011/1603109977095-PM783BB7QO4TM798P4XZ/sarcomere.jpg

Question 5

Explain the banding pattern to be seen in myofibrils

Answer 5

• I-bands - light bands containing only thin actin filaments
• A-bands - dark bands containing thick myosin filaments (and some actin filaments)
• H zone contains only myosin
• Darkest region contains overlapping actin and
  myosin

Question 6

Give an overview of muscle contraction

Answer 6

Myosin heads slide actin along myosin causing the sarcomere to contract. Simultaneous contraction of many sarcomeres causes myofibrils and muscle fibres to contract. When sarcomeres contract (shorten),
* H zones get shorter
* I band get shorter
* A band stays the same
* Z lines get closer

Question 7

Describe the sliding filament theory

Answer 7

FINISH THIS

Question 8

Describe the role of phosphocreatine in muscle contraction

Answer 8

It is a source of inorganic phosphate (Pi), rapidly phosphorylates ADP to regenerate ATP. ADP + phosphocreatine → ATP + creatine. Runs out after a few seconds → used in short bursts of vigorous exercise

Question 9

Compare the structure, location and general properties of slow and fast skeletal muscle fibres

Answer 9

Slow Twitch:
* General Properties: Specialised for slow, sustained contractions (eg. posture, long distance running). Obtains ATP mostly from aerobic
respiration, which releases energy slowly. They fatigue slowly.
* Location: High proportion in muscles used for posture e.g. back, calves. Found in legs of long distance runners.
* Structure: They have a high conc. of myoglobin, which stores oxygen for aerobic respiration. Also have many mitochondria for a high rate of aerobic respiration. Also have many capillaries to supply high conc. of oxygen / glucose for aerobic respiration and to prevent build-up of lactic acid causing muscle fatigue

Fast Twitch:
* General Properties: Specialised for brief, intensive contractions (e.g. sprinting). Obtains ATP mostly from anaerobic respiration, which releases energy quickly. They fatigue quickly due to high lactate conc.
* Location: High proportion in muscles used for fast movement e.g. biceps eyelids. Found in legs of sprinters.
* Structure: They have low levels of myoglobin, and lots of glycogen which is hydrolysed to provide
glucose for glycolysis / anaerobic
respiration which is inefficient so large quantities of glucose is required. There is a high conc. of enzymes involved in anaerobic respiration within the cytoplasm, They also store phosphocreatine