Muscle contraction Flashcards
what are the 3 actions proteins are responsible for
contractile proteins, regulatory proteins, structural proteins
what are contractile proteins
myofibrils- myosin and actin, myosin binds to actin allowing thin filaments to slide between the tick filaments during muscle contraction
what are regulatory proteins
they turn contractions on and off, troponin and tropomyosin- under resting condition covers up the binding sites on the actin protein- prevents binding, for contraction to occur these 2 proteins need to move position (allowing binding)
what are structural proteins
they provide alignment, elasticity, and extensibility to the sarcomere,e.g. TITIN, myomesin, nebulin and dystrophin
proteins of the muscle- myosin
thick filaments are composed of myosin, each molecule resembles to golf clubs twisted together, they are held in place by the M line proteins, the tail binds to other myosin molecules
what is the head of myosin made off
it is made of 2 globular protein subunits, reaches the nearest thin filaments
what happens to myosin during contraction
myosin heads interact with actin filaments, forming cross bridges- head pivots, producing motion
proteins of the muscle- actin
thin filaments are made of actin, ropin and tropomyosin, binding site on each actin molecules is covered by tropomyosin in relaxed muscle, prevents binding of myosin ,
what is the first stage of contraction
the first stage of contraction is for calcium ions to bind to troponin, causing troponin and tropomyosin to move away, allowing cross bridges to for
what holds the thin filaments in place
they are held in place by Z lines, from one Z line to the next is a sarcomere
proteins of the muscle- titin
this anchors thick filaments to the M line and the Z discs, the portion of the molecule between the Z discs and the end of the thick filament can stretch up to 4 times its resting length, and spring back, unharmed
titin role in muscle contraction
role in recovery of muscle from being stretched, therefore important in eccentric muscle contractions
other structural proteins- m line
myoemsin protein, connects to titan and adjacent thick filaments
other structural proteins- nebulin
it is an inelastic protein helps to align thin filaments
other structural proteins- dystrophin
links thin filaments to sarcolemma and transmits tension generated to the tendon
sliding filament mechanism of contraction- 1
myosin cross bridges pull on thin filaments, thin filaments slide inwards towards the M line, between thick filament, z discs move closer together
sliding filament mechanism of contraction- 2
sarcomere shortens. the muscle fibre/ muscle shortens , thick and thin filaments do not change in length- width of A band stays the same
what is the contraction cycle
repeating sequence of events that causes the thin filaments to slide between thick filaments
steps of contraction cycle
exposure of active sites, ATP hydrolysis into ADP and Pi, attachment of myosin to actin forming cross bridges, power stroke- pivoting of the myosin, pulling the thin filaments, detachment of myosin and actin, reactivation of myosin
how long does the contraction cycle go on for
cycle keeps repeating as long as there is ATP available and high Ca+ level nera thin filament
Stages of contraction cycle- 1
nerve impulses arrives at axon terminal motor neuron and triggers release of acetylcholine (ACh)
Stages of contraction cycle- 2
Ach diffuses across synaptic cleft, binds to its receptors in the motor end plate, and triggers a muscle action potential
Stages of contraction cycle- 3
acetylcholinesterase in synaptic cleft destroys ACh so another muscle action potential does not arise unless moreAch is released from the motor neuron
Stages of contraction cycle- 4
muscle AP travelling along T tubule opens Ca2+ release channels in the sarcoplasmic reticulum membrane which allows calcium ions to flood into the sarcoplasm
Stages of contraction cycle- 5
Ca2+ binds to troponin on the thin filaments, exposing the binding site for myosin.
Stages of contraction cycle- 6
contraction: power strokes use ATP; myosin head bind to actin, swivel, and release: thin filaments are pulled toward center of sarcomere
Stages of contraction cycle- 7
Ca2+ release channels in SR close and Ca2+ active transport pumps use ATP to restore low level of calcium ions in sarcoplasm
Stages of contraction cycle- 8
troponin- tropomyosin complex slides back into position where it blocks the myosin binding sites on actin
steps of relaxation- 1
acetylcholinesterase (AChE) breaks down ACh within the synaptic cleft, muscle action potential increases
steps of relaxation- 2
Ca+ release channels close, Ca+ detaches from troponin
steps of relaxation- 3
active transport pumps Ca+ back into storage in the terminal cisternae of the sarcoplasmic reticulum, Ca+ concentration falls
steps of relaxation- 4
calcium binding protein (calsequestrin) helps hold cA+in the SR, tropomyosin- troponin complex recovers binding site on the actin molecules
steps of relaxation- 5
contraction ends, relaxation occurs, muscle returns passively to resting length
Optimal length of muscle fibre
optimal overlap of thick and thin filaments, produces greatest number of cross bridges and greatest amount of tension
Past optimal length of muscle fibre
as stretch muscle (past optimal length), fewer cross bridges exist and less force is produced
under optimal muscle fibre length
if muscle is overly shortened (less than optimal), fewer cross bridges exist and less force is produced, thick filaments crumpled by Z discs
Normal length of muscle fibre
resting muscle length remains between 70-130% of optimal length
what is the length of tension curve
graph of force of contraction (tension) versus length of sarcomere
length of tension curve explained
optimal overlap at the top of the graph, when the cell is too stretched and little force is produced, when the cell is too short, little force is produced- sarcomere cannot shorten any further- no power stroke
what is ATP used for in cells
it supplies energy for muscle contraction and the active transport of calcium ion pumps in the sarcoplasmic reticulum
3 sources of ATP production within the muscle
creatine phosphate, anaerobic cellular respiration, aerobic cellular respiration
what is excess ATP convert to
excess ATP within resting muscle used to form creatine phosphate
what is creatine phosphate
CP 3-6 times more plentiful than ATP within muscle, it is quickly broken down provides energy for creation of ATP , it sustains maximal concentration for 15 secs
anaerobic cellular respiration
ATP produced from glucose breakdown into pyruvic acid during glycolysis, if no O2 is present, pyruvic converted into lactic acid which diffuses into blood
how long can glycolysis provide energy for
glycolysis can continue to anaerobically tO provide ATP for 30-40 seconds for maximal activity
What is aerobic cellular respiration
ATP for any activity lasting longer than 30 seconds, if sufficient oxygen is available, pyruvic acid enters the mitochondria to generate ATP, water and heat, fatty acids and amino acids can also be used by the mitochondria
What does the aerobic cellular respiration provide energy for
it provides 90% of ATP energy if activity lasts more than 10 minutes
