Muscles Flashcards
if the response needed is movement, the CNS sends
signals aling neurones to tell skeletal muscles to contract.
skeletal muscle is made up of
large bundles of long cells called muscle fibres (cell membrane is called the sacrolemma)
bits of the sacrolemma fold inwards acorss the muscle and stick into the sacroplasm - these folds are called?
transverse (T) tubules that help spread electrical impulsed throughout the sactoplasm so they reach all parts of the muscle fibre.
a network of internal membranes called..
sacroplasmic reticulum runs through the sacroplasm which stores and releases calcium ions that are needed for muscle contraction.
muscle fibres have lots of
long cylindrical organelles called myofibrils made up pf proteins and are highly specialised for contraction.
muscle fibres have a lot of mitocondria to
provide ATP needed for muscle contraction
under a microscope dark bands and light bands are visible which contain
dark bands contain the thick myosin filaments and some overlap with actin filaments - A bands
light bands contain thin actin filaments only - i bands
myofibrils contain thick and thin myofilaments that move past eachother to make muscles contract:
thick: made up of the protein myosin
thin: made up of the protein actin
the ends of each sacromere is marked with a
Z line.
a myofibril is made up of many short units called
sacromeres
the middle of each sacromere is an
M line - middle of myosin filaments
around the M line is the
H zone - only contains myosin filaments
actin filaments have binding sites bro
myosin heads called actin myosin binding sites
myosin and actin filaments do what
slide over one another to make the sacromeres contract.
the simultanious contraction of lots of sacromeres means
the myofibrils and muscle fibres contract
contracted sacromeres:
what happens to the A , I and H zones
sacromere hets shorter - a bands stay the same length, I bands get shorter and H zones get shorter.
myosin filaments have
globular heads and binding sites one for actin and one for ATP.
2 other proteins called
tropomyosin and troponin between actin filaments - they are attached to eachother and help myofilaments move past each other.
in a resting muscle, the actin myosin site
is blocked by tropomyosin which is held in place by troponin - myofilaments cant slide because the myosin heads cant bind to the actin filaments.
when an action potential from a motor neurone stimulates a muscle cell, it
depolarises the sacrolemma and it spreads down the T-tubules to the sacroplasmic reticulum.
1 - depolarisation causes the sacroplasmic reticulum to release
stored calcium ions into the sacroplasm
2 - calcium ions bind to troponin, causing it
to change shape - pulls the attached tropomyosin out of the action-myosin binding site on the action filament
3 - exposed binding site allows
myosin head to bind
4 - the bond formd when a myosin head binds to an
actin filament is called action-myosin cross bridge.
5 - calcium ions activate the enzyme
ATPase which breaks down ATP into ADP and Pi to provide the energy needed for muscle contraction.
6 - the energy released from ATP moves the myosin head which
pulls the actin filament along in a kind of rowing action.
7 - atp also provides the enrgy to
break the actin-myosin cross bridge so the myosin head detaches from the actin filament after its moved.
8 - the myosin head then reattaches to
a different binding site further along the actin filament - a new actin-myosin cross bridge is formed and the cycle is repeated
9 - many cross bridges form and break rapidly
pulls the actin filament along and shortens the sacromere causing the muscle to contract
10 - the cycle continues as long as
calcium ions are present to bound to troponin
when excitation stops…
1 - when the muscle stops being stimulated,
calcium ions leave their binding site on the troponin molecules and are moved by active transort back into the sacroplasmic reticulum
when excitation stops…
2 - the troponin molecules return to their original shape,
pulling the attached troponin molecules with them - tropomyosin molecules block the actin-myosin cross briges.
when excitation stops…
3 - muscles arent contracted because
no myosin heads are attached to action filaments
when excitation stops…
4 - the actin filaments
slide back to their relaxed position which kengthens the sacromere.
energy is needed for muscle contraction as ATP gets used up quickly - theres 3 ways it can be continually generated so excersize can continue
1 - aerobic respiration
2 - anareobic respiration
3 - ATP - Creatine Phosphate system
aerobic respiration
most ATP is generated via
oxidative phosphorylation in the cells mitochondria - it only wors when theres oxygen so ita good for long periods of low intensity excersize
anareobic respiration
4 points
ATP made rapidly by glycolysis
end product of glycolysis is pyruvate - converted to lactate by fermentation
lactate can quickly build uo in the muscles and cause muscle fatigue
good for short periods of hard excersize
atp-creatine phosphate
4 points
ATP is made by phosphorylating ADP - adding a phosphate group taken from CP.
CP is stored inside cells and the ATP-CP system generates ATP quickly
CP runs out after a few seconds - used during short burts of vigorous excersize
ATP-CP system is anaerobic and alactic
neuromuscular junctions
1 - neuromuscluar junction is…
a synapse between a motor neurone and a muscle cell.
neuromuscular junctions
2 - neuromuscular junctions use the neurotransmitter
ACh - binds to receptors called nicotinic cholinergic receptors
neuromuscular junctions
3 - neuromusclular junctions work in the same way as
synapses between neurones they release neurotransmitters which trigger depolarisation in thepost synaptic cell
neuromuscular junctions
4 - depolarisation of a muscle cell always causes it to
contract if the treshold level is reached
neuromuscular junctions
5 - acetylcholinesterase stored in the celfts of the post synaptic membrane is
released to break down acetlycholine after use
neuromuscular junctions
sometimes a chemical may block the release of a neurotransmitter or affect the way it
binds to the receptirs on the postsynaptic membrane - prevents action potential from being passed onto the muscle so it wont contract.
neuromuscular junctions
if muscles cant contract, ventilation cant take place
and the organism cant respire aerobically
