muscular system physiology Flashcards
why do skeletal muscles cells contract?
the muscle cells contract in responce to a stimulas from a motor neuron
where do motor neuron communicate with muscle cells?
neuromuscular junction and then the motor unit contracts
what is a motor unit?
motor neuron and the muscle fibres it stimulates
what difference can motor unit have?
some have only a few muscle cells which permits precise motor control and other units have many muscle cells which allows for powerful contractions or gross motor movement
at the neuromuscular junction a motor neuron releases what neurotransmitter?
acetylcholine
what triggers the release of ACh?
Ca+ influx into neuron
at the neuromuscular junction ACh molecules bind to what?
bind to ACh receptor’s on muscle cell membrane
at the neuromuscular junction binding of ACh to muscle cell membrane triggers what?
triggers an action potencial in the muscle cell
what is the muscle cell membrane potencial?
charge difference across cell membrane due to differences in ion distribution which is a form of potencial energy
changes in the membrane potencial can cause what?
can generate an action potencial which is a sudden change in membrane potencial of an editable cell due to Na+ influx which leads to depolarization
muscle cell action potentials occur when?
muscle cells are stimulated by motor neurons
what is excitation?
is an action potencial which through t-tubules triggers Ca+ release which causes crossbridge formation which causes muscle contraction
what is the 1st step in muscle cell excitation?
Na influx causes muscle cell depolarization
action potencial= excitation
what is the 2 step in muscle cell excitation?
action potentials spreads over sacrolemma to t-tubules
what is the 3 step in muscle cell excitation?
a.p triggers Ca+ release from cisternae of sarcoplasmic reticulum
what is the 4 step in muscle cell excitation?
Ca+ causes crossbridge formation between actin and myosin filaments
what is the 5 step in muscle cell excitation?
filaments slide (sacromenes shorten) which gives muscle contraction
how does muscle contraction occur then?
when filaments slide and sacromeres shorten
what happens with relaxed muscles within sliding of filaments?
myosin binding sites on actin are blocked by troponin-tropomyosin complex
what happens after mysoin binding sites are blocked by troponin?
Ca++ release and binds to troponin and the tropomyosin shifts and myosin binding sites are exposed
after myosin binding sites are exposed what is crossbridge formation?
mysoin head latches on and binds to the actin filament
after the myosin head latches on what is the powerstroke?
actin filaments slides along myosin filament and is repeated many times
how does the breaking of crossbridges occur?
triggered by the binding of ATP to myosin
how does the myosin head get recocked?
ATP is used and hydrolized to ADP + P
what does the contraction of a whole muscle require?
requires stimultaneous contraction of many motor units
what is a muscle twitch?
simultaneous contraction of motor units triggered by a single stimulas
what is the latent phase of a muscle contraction?
t-tubules depolarize Ca++ released, muscle cannot respond to another stimulas
what is the contraction phase of a muscle contraction?
sacromeres shorten and tension increases
what is the relaxation phase of a muscle contraction?
Ca++ trasnported back into cisternae of SR
what happens if more motor units are recruited?
more motor units stimulate more muscle fibres which creates a stronger contraction and tension icreases
what is tension?
force excerted by a contracting muscle measured in grams
what affects the amount of tension?
- muscle length (amount of stretch)
- strength of stimulas because of motor unit recruitment
- frequency of stimulas because of motor unit recruitment
steps in muscle cell contraction?
- muscle cell action potencial
- causes Ca++ to release from SR
- causes filaments to slide
- contraction continues as long as Ca++ levels are high
steps in muscle cell relaxation?
- stimulas stops(no action potencial)
- active transport of Ca++ back into sacroplasmic reticulum (ATP used)
- crossbridges can no form (tropomyosin covers binding sites) filaments seperate
- repolarization of muscle cell (Na/k transporter restores resting membrane potencial) ATP used
how does moderate stretch affect tension?
maximum number of crossbridges can form (maximum tension)
how does unstretched muscle affect tension?
fewer crossbridges can form (low tension)
how does overstretched muscle affect tension?
no overlap between actin/myosin, no crossbridges means no tension
how does the strength of the stimulas affect tension?
stronger stimulas= increased motor unit recruitment
smaller motor units recruited first then larger ones
what varries for different motor units?
threshold
