Muscles Flashcards
What are the 3 types of muscles in the body?
Skeletal = makeup bulk of body –> responsible for movement
Cardiac = only in heart –> myogenic
Smooth = found in the walls of organs + vessels
Describe structure of skeletal muscle:
Made of bundles of muscle fibres enclosed in plasma membrane (sarcolemma)
Contain number of nuclei
Longer than normal cells
Shared cytoplasm = sarcoplasm
Lots of mitochondria = ATP to contract
Sarcoplasmic reticulum = Ca+ required for contraction
What are T-tubules
Parts of sarcolemma folded inwards
–> help spread electrical impulse throughout sarcoplasm
Ensures whole fibre receives impulse to contract at same time.
What are myofibrils?
Long cylindrical organelles made of proteins –> specialised for contraction.
Parallel= max force
What are myofibrils made out of?
Actin –> thinner filament –> two strands twisted around each other
Myosin –> thicker filament –> long rod-shaped fibres with bulbous heads that project to one side
What are the different bands in skeletal muscles?
Light bands = actin + myosin do not overlap
Dark bands = presence of thick myosin filaments
—–>edges particularly dark as myosin overlap with actin (A band)
Z-line = found in centre of each light band.
–> distance between each adjacent Z-line = sarcomere
H-line= ligher region found in cenre of each dark band
–> only myosin filaments present
What does the sarcomere do?
Shortens when muscle contracts
What happens to the H-zone when muscle contracts?
Decreases
Summarise the structures once more pls :>
Sarcomere –> basic functional unit of fibre
Sarcolemma –> plasma membrane around fibre
Sarcoplasm –> shared cytoplasm within fibre
Sarcoplasmic reticulum –> endoplasmic reticulum in sarcomere
Describe structure of actin:
Actin filament wrapped around by tropomyosin
Held in place by troponin
–> bind to Ca2+ = conformational change
Dents in filament = actin-myosin binding site
Describe structure of myosin
Myosin head binds to actin filament
ADP bind to head
Has ATPase component
–> forms cross-bridges with actin at AM binding site
What happens in the stimulation stage of sliding filament model?
AP arrives
AP depolarises sarcolemma + sarcoplasmic reticulum
Voltage-gated Ca2+ on SR open to release Ca+ into sarcoplasm
Ca2+ binds to troponin
Causes conformational change
—> pulls on tropomyosin —> exposes actin-myosin binding site.
What happens in attachment stage of sliding filament model?
Myosin head binds to A-M binding site forming cross-bridges
Myosin filament flexes—> pulls actin along
Releases ADP
What happens in the detachment stage of sliding filament model?
ATP binds to myosin head –> causes it to detach from A-M binding site on actin
Ca2+ activates ATPase in myosin head
ATP hydrolysed to form ADP + Pi
Energy released from ATP hydrolysis returns myosin head back to OG position
What is a neuromuscular junction?
where a motor neurone
and a skeletal muscle fibre meet
