Muscles Flashcards
Skeletal muscle description
Voluntary muscle that is striated
Attached to bones by tendons
Contracts in response to release of acetylcholine from a motor neurone
Muscles only pull so opposing muscle group needed that pull in the opposite direction
Muscle group contracting called - agonist
Muscle group relaxing called - antagonist
Structure of skeletal muscle
Composed of many muscle fibres bound together by connective tissue muscle fibres are highly specialised
Long thin cells that contain many nuclei
Each muscle fibre surrounded by sarcolemma and nuclei are just beneath it
Cytoplasm is called sarcoplasm which has a lot of mitochondria
Muscle fibres contain large number of myofibrils surrounded by sarcoplasmic reticulum
Divided into thick and thin myofilaments
Why does the sarcoplasm have a large number of mitochondria
Lots of atp needed for muscle contraction
Role of the sarcoplasmic reticulum
Delivers calcium ions inside myofibrils to cause contraction
Sarcomere
Embedded throughout whole structure
Unit of contraction
Shortening = contraction
Thin and thick filaments
Actin(thin)
Myosin(thick)
What happens to each element as sarcomere contracts
A band - stays the same
I band - shortens
H zone - shortens
Z lines - get closer together
Sarcomere - shortens
When does sliding filament theory occur
If muscle fibre is excited by a motor neurone sliding filament theory can occur
Sliding filament theory
- ca2+ released from the sarcoplasmic reticulum into sarcoplasm
- ca2+ diffuse and causes tropomyosin to move exposing myosin head binding site on actin filaments
- myosin heads bind to actin binding site forming actinomyosin cross bridges
- myosin head mods pulling actin filament a short distance ( power stroke)
-adp and pi are released from myosin head - new atp binds to myosin head
- this breaks cross bridge and separates it from actin
-atp hydrolysed to adp and pi and energy released recocks myosin head (recovery stroke) - process repeats pulling actin along myosin filament a bit more each time
What is atp required for in muscles
Sliding of filaments during contraction
Active transport of calcium ions into sarcoplasmic reticulum
What happens if not enough atp can be made for muscle contraction
An alternative biochemical pathway is found
Phosphocreatine can donate a phosphate to adp regenerating atp in the short term
Phosphocreatine can be regenerated using atp when it can’t be supplied via aerobic respiration
Slow twitch fibres
Produce slow sustained contractions over long periods but have slow rate of contraction
Slow to fatigue
Found in muscles in the leg and those involved in maintaining posture
Specialised slow twitch fibres
-Use aerobic respiration energy system to regenerate atp
Have many large mitochondria just under sarcolemma to provide atp for active transport
- High concentrations of myoglobin - acts as oxygen store
- closely associated with large number of capillaries to provide good oxygen supply
- less extensive sarcoplasmic reticulum - less calcium ions needed at one time
- less glycogen as glucose broken doesn’t fully via aerobic respiration
Fast twitch fibres
Rapid strong contractions as have faster speed of contraction only sustained over short time periods
Fast to fatigue due to build up lactate
Specialised fast twitch fibres
- specialised to use / PC-ATP anaerobic respiration energy systems to regenerate atp
-have fewer smaller mitochondria - low conc of myoglobin as primary energy systems are anaerobic
- fewer capillaries associated with fibres
- extensive sarcoplasmic reticulum as more ca2+ ions needed as aerobic respiration at one time for rapid intense contraction
- more glycogen as more glucose required as aerobic respiration yields less atp per molecule
