muscles Flashcards
what are the 3 types of muscle
-smooth
-cardiac
-skeletal
what is smooth muscle
-contracts and relaxes automatically
-autonomic control
-not striped
what is cardiac muscle
-muscle of the heart
-myogenic - own electrical impulse
-contracts and relaxes automatically
what is skeletal muscle
-stripped appearance and voluntary muscle
-we have direct control over it
what a are skeletal muscles joined to the bone by and what are the types
tendons
-2 types of tendon
-origin - attaches muscle to the stationary bone
-insertion - attaches muscle to the bone that moves
how are muscles antagonistic pairs
-the muscle that contracts is the agonist/prime mover
-the muscle that relaxes is the antagonist
-one muscle that acts as an agonist for one movement acts as the antagonist for the opposite movement
-muscles can only contract and relax - they cannot push
what are muscles that cause joints to bend called
flexors
what muscle causes joints to straighten called
extensors
how do the biceps and triceps show antagonistic muscle action
-when bicep contracts - elbow joint bends
-at the same time the triceps relaxes and becomes longer
-when the triceps contracts it straightens the elbow joint and pulls the bicep to make it longer
what is the structure of the muscle
-main body is known as the muscle belly
-muscle belly is surrounded by a large layer of connective tissue - contains nerves and blood vessels and eventually forms tendons
-muscle belly made up of fasiculi - each fasiculus is a bundle containing long cylindrical muscle cells called muscle fibres
-can be up to 10-100 nm and 30 cm long
what is the membrane in a muscle cell known as
sarcolemma
what does each muscle cell contain
-sarcoplasm - cytoplasm of muscle cell
-many nuclei as each cell is formed from many cells fused tg
-many mitochondria to produce ATP
-glycogen stores for energy generation
-myoglobin stores for extracting oxygen from the blood
-protein fibres called myofibrils giving the muscle a striped appearance
what is the role of myoglobin
-to pick up oxygen from haemoglobin as it has a higher affinity for oxygen that Hb
what are the 2 things that make up myofibrils
-myosin
-actin
what is myosin
thick filaments that are 15nm in diameter
-around 200 joined tg
-has long tail and double head which can attach to binding sites on the actin
-heads contain ATPase which hydrolyses ATP into ADP and Pi
-the long tails form the bulk of the thick filament and the heads stick out from the surface
-when the myosin is relaxed the heads have ATP attached to them
what is actin
-thin filaments 7nm in diameter
-2 threads of actin coiled around each other
-at each twist there is a myosin binding site where myosin can become attached to the actin
-in relaxed muscle these binding sites are covered by two other proteins called troponin and tropomyosin - these can block the myosin binding sites
what is the actin and the myosin arranged into
-sacromeres - which is the smallest contracting unit of the skeletal muscle
-this causes a banding pattern which can be seen on an electron microscope
what are the colours of the bands of myofibrils that can be seen
-where myosin and actin overlap = dark band
-myosin only = lighter band
-actin only = even lighter band
what are the M and Z lines in a myofibril diagram
-Z is where the actin takes place
-M is where the myosin is anchored in place
what are letters given to the bands in a myofibril diagram
-I band = actin filament only
-H band = myosin only
-A band = actin and myosin overlap
-sacromere = distance bwt the Z lines
what is the theory given to muscle contraction
-sliding filament theory
describe the sliding filament theory - detailed
-contraction is initiated by a nerve impulse arriving at a neuromuscular junction
-this causes the release of acetylcholine at the synapse of the neuromuscular junction
-this diffuses across the synaptic cleft and binds to specific comp receptors in the sarcolemma which is then depolarised
-the sarcolemma forms a series of infoldings called t-tubules and the wave of depolarisation spreads across these tubules and onto the sarcoplasmic reticulum inside the muscle
-the sarcoplasmic reticulum releases Ca2+ ions into the sarcoplasm this has 2 effects
-the Ca2+ ions change the shape of the troponin and tropomyosin causing them to fall of the actin filaments exposing the myosin binding sites
-the Ca2+ ions directly act on myosin activating it so that it breaks down the ATP via ATPase to release energy - this cause the myosin head to tilt forward towards the exposed binding sites on the actin filament
-cross bridges form bwt the myosin heads and the actin filaments
-as the cross bridges form the myosin heads rotates and they change position - the attached actin filament is pulled past the myosin - tis change in conformation of the myosin releases the bound ADP and Pi so the myosin returns to it starting position and attaches to the next binding site - known as ratchet movement
-actin filament is moved along by the myosin
-the actin filaments are detached from the myosin heads and both return to the original positions
-when this stops the Ca2+ ions are pumped back into the sarcoplasmic reticulum and troponin and tropomyosin move back to their original positions blocking the active site - the myosin can no longer bind so both the sacromeres move back to the original position and the muscle relaxes with the help of the antaganostic muscle
what happens when the nerve impulse to the muscle stops
-the acetylcholine is released from the receptor on the sarcolemma by the action of acetylcholinesterase
-the sarcolemma then repolarises and Ca2+ ions are actively pumped back into the sarcoplasmic reticulum
-the levels of Ca2+ ion in the sarcoplasm falls and the troponin and tropomyosin move back into their original position blocking the binding sites`
how does the increasing contraction of the sarcomere change the width of the A and H bands
- A band widens
-H band shortens
how is each muscle connected to the nervous system
by motor neurons
what is a motor unit
each motor neuron combined with the muscle fibres
what does the number of muscle fibres in a motor unit depend on
the degree of control required by the muscle
what is the volume of muscle fibres in a high degree of fine control
-motor neuron
-small or single number of muscle fibres
what is the volume of muscle fibres without a high degree of fine control
many muscle fibres
-large muscles
how does the all or nothing principle relate to muscle fibres
-either contracted or relaxed
-the nervous stimulus recived by the muscles fibres is either strong enoughj to bring about contraction or it isnt
-cannot partially contract
-if the nerve stimulation reaches a critical threshold level the fibres of the motor unit contract
-if not strong enought he motor unit does not respond
what are the 3 ways in which the strength of muscle contarction be altered
-multiple unit stimulation
-temporal stimulation
-synchronisity of motor unit stimulation
how does multiple unit stimulation work
-the more motor units activated the karger the proportion of the muscle which will contract therefore the more powerful movement
how does temporal stimulation work
-the frequency with which the motor units are activated may vary
-muscle twitch occurs when the muscle fibres receive single nerve impulses which exceeds the threshold value then they respond by contracting then relaxing or twitching
-wave summation occurs when the second nerve impulse arrives before the muscle contraction has completed - the muscle fibres not have time to relax before the next contraction starts - add together effective;y to produce a more powerful summation
-muscle tetanus or tetanci contraction occurs went he nerve impulses arrive in quick succession then this leads to a more powerful contraction
how does synchronisity of motor unit stimulation work
-Synchronised contraction occurs when all of the motor units contract simultaneously
-however this means all motor units will become fatigued at the same time and therefore activity can’t be sustained
-asynchronised contraction occurs when different motor units are activated at different times whilst some contract and some relax
-allows muscle activity to be sustained over an extended period of time at a sub-maximal level - so don’t fatigue
describe the sliding filament theory - simpler
-action potential arrives at the neuromuscular junction, aceytlcholine diffuses across the gap and binds to a specific, complementary receptor which opens gated Na+ channels causing depolaristion of the sarcolemma
-the wave of depolarisation spreads down t-tubules causing release of Ca2+ ions from the sarcoplasmic reticulum
-Ca2+ binds to troponin and tropomyosin causing a change in shape moving it away from the actin and expose the myosin binding sites and causes the release of ADP and Pi from the hydrolysis of ATP
-myosin heads bind to actin forming cross bridges
-ADP/Pi falls of myosin causing it to tilt = Powerstroke
-pulls the actin past the myosin
-ATP binds to myosin head causing it to detach from the actin
-ATP is hydrolysed to ADP + Pi
-process repeats with myosin bidnign to next actin site
OVERALL - actin is pulled past the myosin shortening the sarcomere
what are the two main types of muscle fibre
-type 1
-type 2
what are type 1 muscle fibres
-slow twitch fibres
-smaller than type 2 and contract slowly
-dont fatidue as easily as fast ones
-so ideal for low intensity or endurance events
-maintain posture
what are type 2 muscle fibres
-fast twitch fibres
-bigger size
-contract faster producing force more rapidly
-fatgue more easily so they are only useful for short distribution activities with high inensity
type 1 slow twitch characteristics
-small size
-high myoglobin content - pick up lots of oxygen from blood for resp
-high capillary density
-high mitochondrial density -aerobic - oxygen is temrical electron acceptor
-high activity in low intensity
-low glycogen
-low phosphocreatin
-low fatigue
-slow contractile time
-slow relaxation
-slow activity during high intensity
type 2 fast twitch fibre charcateristics
-large size
-low myoglobin
-low capillary density
-low mitochondrial density - anaerobic so glycolysis occurs which is in cytoplasm
-low activity in low intensity
-high glycogen store
-high phosphocreatin level
-high fatigue
-fast contractile time
-fast/high relaxation
-high activity in high intensity
how is the pH of the muscles lowered in vigorous exercise
carbon dioxide is produced
which lowers it
what do slow muscle fibres prefer carb load or creatine
carb load - glycogen store s- so more glucose - more aerobic resp
how does creatine produce ATP
-creatine combines with a phosphate = phosphocreatine/ creatinephosphate
-this then combines with ADP to form ATP
Give two reasons why transmission across a cholinergic synapse is unidirectional.
- (Only) the presynaptic
neurone/knob/membrane releases/has
neurotransmitter/acetylcholine;
2.(Only) the postsynaptic
neurone/membrane has receptors
OR
No receptors in the presynaptic
neurone/membrane;
how does temporal summation trigger a rapid response
(Several/repeated impulses in short
time) provide (enough)
neurotransmitter/acetylcholine to reach
threshold
OR
(Several/repeated impulses in short time)
so (enough) sodium ions enter to reach
threshold
OR
(Several/repeated impulses in short time)
increases membrane potential to reach
threshold;
