6.4 - Skeletal muscles Flashcards
Describe features of skeletal muscles (sometimes called striped or striated)
- voluntary
- joined to bones by tendons
What feature do all muscles share?
pairs are antagonistic
Name the 2 main proteins present in a myofibril and describe them
actin: thin and myosin: thick
What is the sarcolemma?
membrane of a muscle fibre
What is the sarcoplasm?
cytoplasm of a muscle fibre
What is the sarcomere?
one contractile unit of a muscle fibre
What is the A band?
total width of myosin
What is the H zone?
where there is myosin only
What is the I or light band?
where there is actin only
What is the M line?
middle point of myosin
What do Z lines indicate?
the parameters of one sarcomere
Describe what happens to the parts of a myofibril during contraction
- A band stays same
- H zone and I band shorten
- Z lines move closer together
Does the A band ever change?
no, it always stays constant
Describe fast twitch muscles fibres
- fast contractions
- rapid release of energy
- lots of thick myosin filaments
- high glycogen conc -> hydrolysis of glycogen to glucose
- high conc of enzymes involved in anaerobic respiration
- high conc of phosphocreatine to rapidly generate ATP from ADP (quicker production of ATP than slow twitch)
Describe slow twitch muscle fibres
- slow contractions
- long periods of exercise
- large store of myoglobin
- rich blood supply
- lots of mitochondria
- mainly aerobic respiration
Describe the role of phosphocreatine
combines with ADP to form ATP for muscle contraction
Describe how skeletal muscle contracts
- A.P arrives at neuromuscular junction
- Ca2+ ions diffuse into myofibrils from sarcoplasmic reticulum
- causing movement of tropomyosin on actin, exposing actin’s actin-myosin binding sites
- myosin heads attach to binding sites on actin, forming actinomyosin cross bridges
- hydrolysis of ATP on myosin heads causes them to bend, pulling actin molecules in a power stroke
- new ATP molecule attaches to each myosin head
- so myosin heads detach from sites
- ATPase in sarcoplasm (activated by Ca2+ ions) hydrolyses ATP on myosin head so it returns to original position; no more Ca2+ released from sarcoplasmic reticulum
- when no more contraction needed, Ca2+ ions actively transported back into sarcoplasmic reticulum
What else is ATP needed for?
active transport of Ca2+ ions into sarcoplasmic reticulum
Where are fast and slow twitch muscle fibres found?
fast: limbs e.g biceps; human eyelids
slow: calf muscle, back muscle etc.
How does muscle fatigue occur?
- phosphocreatine stores run out
- cell uses ATP made by glycolysis (anaerobic)
- produces lactate, builds up, causes muscle fatigue
