topic 6 muscle contraction Flashcards
what are the three types of muscle?
cardiac, skeletal and smooth
what is skeletal muscle used for?
movement
what do tendons do?
attach muscle to bone
what do ligaments do?
attach bones to bones
why do bones act as levers?
they are incompressible so a lever gives a muscle support to pull against
what is it called when muscles act in pairs?
antagonistic pairs
what is an agonist?
contracting muscle
what is an antagonist?
relaxing muscle
what is an example of an effector?
a muscle
how are muscles stimulated to contract?
by neurons/an action potential
what is skeletal muscle made from?
muscle fibres
what is the sarcolemma?
cell membrane of muscle fibres
what does the sarcolemma do?
folds inwards across muscle fibres and sticks to the sarcoplasm
what is the sarcoplasm?
muscle cell cytoplasm
what are folds of the sarcolemma called?
transverse (T) tubules
what do transverse tubules do?
spread electrical impulses throughout the sarcoplasm to reach all parts of the muscle fibre
what is the sarcoplasmic reticulum?
network of internal membranes that runs through the sarcoplasm, and releases calcium ions for muscle contraction
what organelles do muscle cells have many of?
mitochondria- provide ATP for muscle contraction
multinucleate
what are myofibrils?
long, cylindrical organelles
made up of proteins
bundles of thick/thin myofilaments that move past eachother to make muscles contract
what are thick myofilaments called?
myosin
what are thin myofilaments called?
actin
what can you see when looking at a myofibril under an electron microscope?
alternating light and dark bands
what are the A bands?
thick myosin, some overlapping thin actin
appear dark
what are the I bands?
thin actin, light bands
what is a myofibril made from?
short units known as sarcomeres
what is the end of a sarcomere called?
Z line
what is the middle of a sarcomere called?
M line
what is the H zone?
area either side of the M line
only myosin filaments
what is the sliding filament theory?
myosin and actin filaments slide over eachother which makes sarcomeres contract
simultaneous contractions cause myofibrils and muscle fibres to contract
sarcomeres return to their original length as the muscle relaxes
why do myosin filaments have hinged globular heads?
so they can move back and forth
what do myosin filaments have a binding site for?
actin and ATP
what do actin filaments have a binding site for?
myosin heads, known as the actin-myosin binding sites
where is the protein tropomyosin found?
between actin filaments
helps myofilaments move past eachother
what is the actin-myosin binding site blocked by in a resting muscle?
tropomyosin
what happens because the actin-myosin binding site is blocked in a resting muscle?
myofilaments can’t slide past eachother because myosin heads can’t bind
what are the stages of muscle contraction?
action potential from the motor neuron stimulates the muscle cell
this depolarises the sarcolemma
depolarisation spreads down the transverse tubules to the sarcoplasmic reticulum
so it releases stored calcium ions into the sarcoplasm
calcium ions bind to a protein attached to tropomyosin
so the protein changes shape and pulls attached tropomyosin out of the actin-myosin binding site on the actin filament
this exposes the binding site so the myosin head can bind, forming a bond called the actin myosin cross bridge
calcium ions activate ATP hydrolase which hydrolyses ATP to provide energy for muscle contraction
the energy released from ATP causes the myosin head to bind, and pull along another actin filament
another ATP provides energy to break the actin-myosin cross bridge
the myosin head detaches from the actin filament after it has moved
the myosin head reattaches to a different binding site further along the actin filament
so a new actin-myosin cross bridge is formed and the cycle is repeated
many crossbridges form and rapidly break, which pulls the actin filament along, shortening the sarcomere so the muscle contracts
the cycle continues if calcium ions are present
what happens when excitation stops?
muscle stops being stimulated
calcium ions leave their binding site and move by active transport back to the sarcoplasmic reticulum
what does calcium ions moving back to the sarcoplasmic reticulum do?
causes tropomyosin molecules to move back so they block the actin binding site
muscles aren’t contracted as no myosin heads are attached to actin filaments
no actin-myosin cross bridges formed
actin filaments slide back to their relaxed position which lengthens the sarcomere
which are the three ways ATP can be regenerated for muscle cells?
aerobic respiration
anaerobic respiration
ATP phosphocreatine system
how can ATP be regenerated by aerobic respiration?
regenerated by oxidative phosphorylation in the cell’s mitochondria
happens when oxygen is present
during long periods of low intensity exercise
how can ATP be regenerated by anaerobic respiration?
rapidly made by glycolysis
end product is pyruvate which is converted to lactate by lactate fermentation
lactate quickly builds up resulting in muscle fatigue
during short periods of high intensity exercise
how can ATP be regenerated by the ATP Phosphocreatine system?
phosphorylate ADP by adding a phosphate group from PCr (ATP-Phosphocreatine)
PCr is stored inside cells
the ATP-PCr system quickly regenerates ATP
runs out after a few seconds
used during short bursts of vigorous exercise
anaerobic and alactic system
how do slow twitch muscle fibres contract?
slowly
how do fast twitch muscle fibres contract?
rapidly
what are slow twitch muscle fibres used for?
posture
endurance activities
what are fast twitch muscle fibres used for?
fast movements
short bursts of speed/power
do slow twitch muscles easily tire?
no
do fast twitch muscles easily tire?
yes
which type of respiration do slow twitch muscles perform?
aerobic
which type of respiration do fast twitch muscles perform?
anaerobic
which type of muscle fibres have many mitochondria and blood vessels?
slow twitch
which type of muscle fibres have few mitochondria and blood vessels?
fast twitch
why are slow twitch muscle fibres red?
rich in myoglobin
why are fast twitch muscles fibres white?
little myoglobin
