6.3 Skeletal Muscles Flashcards
(8 cards)
How do muscles work
In antagonistic pairs - pulling in opposite directions (biceps/triceps)
One will contract(agonist)pulling on bone
The other will relax (antagonist)
Skeleton is incompressible so muscles can transmit force to bone
Describe strive of skeletal muscle
Made of many bundle of muscle fibres
Attached to bones via tendons
Muscles fibres contain:
-sarcolemma which folds inwards to form transverse (T) tubules
-sacroplasm
-multiple nuclei
-many myofibrils
-sarcoplasmic reticulum (ER)
-many mitochondria
Structure of myofibril
Made of 2 types of protein filaments:
-myosin (thick)
-actin(thin)
Arranged in sacromeres:
-ends are Z lines
- middles is M line
- H zone contains only myosin
Banding pattern in myofibrils
I bands - light bands, only thin actin
A-bands, dark with thick myosin (and some actin)
H zone contains only myosin
Darkest region is the myosin and actin overlapping
Over view of Muscles contraction
Myosin heads slide actin along myosin causing the sarcomere to contract
Lots of contrast of many sarcomeres causes myofibrils and muscles fibres to contract
When sarcomeres contract:
-H zones get shorter
-I band gets shorter
-A band stays the same
- Z lines get closer
Explain muscle contraction
Depolarisation speeds down sarcolemma via T tubes causing Ca to release from SR which diffuse into myofibrils
Calcium binds to tropomyosin causing it to move, this exposes the binding sites on actin
Myosin heads (with ADP) bind to the binding sites on actin forming an actinomyosin cross bridge
Myosin heads change angle pulling along myosin (ADP realised) using energy from ATP hydrolysis
New ATP binds to myosin heads change angle causing it to detach from actin
Hydrolysis of ATP (ATPhydrolase activated by Ca ions) releases energy energy from myosin head to return to original position
Myosin reattaches to diffrent binding sites further along action
This cycle continues as long as calcium conc is high
Role of phosphocreatine in muscle contraction
A source of inorganic phosphates rapidly phosphorylates ADP to regenerate ATP
-ADP to phosphocreatine = ATP and creatine
Runs out after a few seconds - used in shorts bursts of exercise
Anaerobic and alactic
Structure, location and properties of slow and fast twitch
Slow:
-slow sustained contractions (long distance running)
-produces ATP slowly from aerobic respiration
-fatigues slowly
Location:
-posture (back calves)
-legs of long distance runners
Structure:
-high conc of myoglobin (stores O for aerobic respiration)
-lots of mitochondria
-lots of capillaries (supply high conc of O and glucose) and prevents build up of lactic acid
Fast:
-fast intensive contractions (sprints)
-produce less ATP faster (anaerobic)
-fatigues quickly (high lactate conc)
Location:
-fast muscles (biceps and eyelids)
Structure:
-low levels of myoglobin
-lots of glycogen (hydrolysed for glucose for anaerobic)
-high conc of enzymes for anaerobic
-store phosphocreatine
