Skeletal Muscles Flashcards
What are the different types of Muscles?
Skeletal
Smooth
Cardiac
What is the job of the Skeletal Muscle?
Moves the body’s skeleton
When the muscle contracts (shortens) the tendon pulls on joints causing movement
Structure of Skeletal Muscle
Basic structure = sarcomeres made up of actin and myosin, actin is thin and has tropomyosin wrapped around it
Myosin is thick and has heads, when the sarcomere contracts the whole muscle contracts, contracts/shortens by the sliding filament mechanism
Many sarcomeres = myofibril
Many myofibrils = muscle fibre
Surrounded by a membrane called the sarcolemma
contains myofibrils, fluid called sarcoplasm, and tubes called the sarcoplasmic reticulum
Many muscle fibres = bundle of his
many bundles = whole muscle
Locations in a Sarcomere
A band = location of myosin [no change in contraction]
I band = location between the myosin [shortens in contraction]
H zone = location between the actin [shortens in contraction]
Z line = end line of sarcomere [moves closer together in contraction]
What occurs in the Sliding Filament Mechanism?
How the sarcomere shortens
The myosin heads pull the actin inwards
The motor neurone connects to the skeletal muscle via a neuro-muscular junction
Releases acetylcholine that binds to complementary receptors on the muscle fibre membrane (sarcomere)
Na+ channels open, Na+ ions enter the muscle fibre causing depolarisation
a wave of depolarisation travels through sarcoplasmic reticulum
causes the release of Ca2+ ions into the sarcoplasm (fluid surrounding sarcomeres/myofibril)
This moves the tropomyosin on the actin, which exposes binding sites on the actin
Myosin heads now bind to the actin (form actin-myosin cross bridge) with the myosin pulling the actin inwards
ATP attaches to the myosin head so it detaches
ATP broken down by ATPase to release energy, which causes myosin head to go back to its original position
So it reattaches, pulling the actin further inwards
Role of Ca2+ ions and ATP in muscle contraction
Ca2+ ions cause the tropomyosin to move exposing binding sites on actin
Ca2+ ions stimulate ATPase
ATP causes the myosin head to detach
ATP releases energy so the myosin head returns to its original position
ATP actively transports Ca2+ ions back into the sarcoplasmic reticulum when the muscle is relaxed
How do Fast Twitch Muscle Fibres work?
Provide powerful but short-lasting contractions
found in biceps and sprinters
adapted for anaerobic respiration
has thicker myosin for powerful contractions
contains more enzymes for anaerobic respiration
contains phosphocreatine, provides phosphate to ADP to reform ATP
How does Slow Twitch Muscle Fibres work?
Provide less powerful but long-lasting contractions
Found in thigh muscles and marathon runners
adapted for aerobic respiration
has a rich blood supply
contains many mitochondria
contains glycogen
contains myoglobin (stores oxygen)
