Muscles Flashcards
How are sarcomeres positioned
Run adjacent to eachother
Along length of myofibril
Example of an antagonistic pair
Bicep
Tricep
What is dystophin
Prevents membrane damage when muscle contracts
What is duchenne muscular dystrophy
A genetic mutation, X linked recessive disease
Causes dystrophin to be extremely short
Usually lacking dystroglycan binding end
So every time muscle contracts small rips appear in membrane
Allowing for diffusion of molecules
Calcium diffuses in and activates enzymes called proteases that break down proteins
Instead of breaking old and non functional proteins they also break down new functional proteins
Creatine kinase leaks out of myocyte and into blood and can be uses to identify DMD
Meaning less energy storage occurs
What type of neurone stimulates muscle contraction
Motor neurone
What is the power stroke
The myosin head changes angle and bends to pull the actin filament a short distance over itself
What is the recovery stroke
When ATP is hydrolysed into ADP and Pi by ATP hydrolase
And the energy released re cocks the myosin head
Advantages of using aerobic respiration instead if anaerobic to provide ATP in a long distance race
Waste product carbon dioxide is easily removed from body during aerobic respiration
Aerobic respiration releases/produces more ATP
Lactate will not accumulate in the body so avoids cramps
Why does converting pyruvate into Lactate allow the continued production of ATP by anaerobic respiration
Regenerates NAD
Glycolysis continues
ATP can be produced via substrate level phosphorylation
Why can’t cross bridges between actin and myosin be broken after death
No respiration after death
ATP required to break cross bridges
What happens to the length of the I band and A band when sarcomeres contract
Neither change in length
3 types of muscle
Smooth; contracts without conscious control, in walls of internal organs like stomach and intestines
Cardiac; contracts without conscious control, myogenic, only found in the heart
Skeletal; striated muscle used in locomotion like biceps and triceps and work in antagonistic pairs
What are antagonistic pairs
Pair of muscles
As one contracts the other relaxes
Since muscles can only pull
How are skeletal muscles attached to bone
Tendons
Fibrous proteins
Key structures of the skeletal muscle
Bone Tendon Muscle: Sarcolemma Sarcoplasm Myofibril Myofilament Actin and myosin
How are muscle cells specialised
Long thin cells
Several nuclei
Sarcolemma
Each muscle fibre is surrounded by this thin cell membrane
Epimysium
Protective layer surrounding muscles that protects from friction against other muscles and bones
Continues at the end of the muscle go form tendons along with other connective tissue that connects muscle to bone
Endomysium
Fibrous connective layer of tissue covering each muscle fibre
Insulates each fibre
What can be found on the Sarcolemma
Acetylcholine receptors
Sarcoplasm
Contains a large number of mitochondria, organelles, nuclei, sarcoplasmic reticulum
Myofibrils
Run parallel to each other along the length of muscle cells
Surrounded by sarcoplasmic reticulum
Made of myofillaments that are divided into thick (myosin) and thin (actin) myofilaments
What are sarcomeres
Run adjacent to eachother along the length of the myofibril
Contractile units made of mypfilaments actin and myosin
Sarcoplasmic reticulum
Stores and releases calcium ions for muscle contraction
Striated
Under light microscopes dark bands are visible across the muscle fibre
Under electron microscopes dark bands are visible across each myofibril
Each darcomere had a distinctive banding pattern due to the presence or absence of thick and thin filaments
What is the result of the sliding filament theory
Sarcomere shortens Z lines closer Actin pulled over myosin Increased overlap means appears darker Filaments the same size
Explain a relaxed myofibril
Tropomyosin covers the binding site on actin filament which myosin attaches to
Explain the sliding filament theory
Muscle fibre excited by a motor neurone
Ca²+ released from sarcoplasmic reticulum
Into sarcoplasm
Ca²+ diffuses and binds to troponin
Conformational change in shape
Causes tropomyosin to move
Exposing myosin heads binding sites on actin filament
Myosin head binds and forms a cross bridge
Nods and bends to pull actin filament over itself in the power stroke
ADP and Pi released from myosin head
New ATP binds and breaks the cross bridge
Myosin separates from actin
ATP hydrolysed to ADP and Pi by ATP hydrolase
Energy released re-cocks the myosin head in recovery stroke
Process repeats to pull actin over myosin a bit more each time
Shortening of sarcomere
FINISH
Explain Ca²+ in muscles
Actively transported back into the sarcoplasmic reticulum
Activate ATP hydrolase
Bind to troponin and cause a conformational change in shape to tropomyosin to uncover the myosin head binding site
Why can producing less ATP mean people aren’t able to maintain strong muscle contractions during exercise
ATP is needed for attachment and cross bridges between actin and myosin
Power stroke in which myosin head bends to pull actin over it from ATP hydrolysis
Dectachment of myosin heads when new ATP binds
Myosin heads move back to original position in recovery stroke
Describe the role of tropomyosin and myosin in myofibril contractions
Tropomyosin:
Moves out of the way when calcium ions bind to troponin
Allowing myosin head to bind and form cross bridge
Myosin:
Myosin head inds to actin and performs power stroke to pull actin over itself
Myosin head detaches and resets in recovery stroke
Uses ATP
Why do mitochondria in muscles contain many cristae
Large face area for the electron transport stem/oxidative phosphorylation
Provides ATP needed for muscle contraction
Why does increased cardiac output give an advantage in exercise
In exercise more energy released/more respiration/more oxygen for aerobic respiration
Higher cardiac output means more oxygen supplied to muscles
Increased glucose supply to muscles
Increased carbon dioxide removed and more lactate removed
Increases heat removal for cooling
Importance of ATP hydrolase in muscle contraction
Hydrolyses ATP yielding energy
Used to break cross bridges
What are the advantages of using aerobic rather than anaerobic respiration to provide ATP for long distance races
Aerobic respiration releases more energy/produces more ATP
Little/no lactate produced so doesn’t accumulate
Avoiding cramps and muscle fatigue
CO2 removed easily from the body by breathing
A muscle fibre contracts when it is stimulated by a motor neurone
How does transmission occur across the synapse between the motor neurone and a muscle fibre
Calcium ion channel proteins open
Calcium ions enter neurone by facilitated diffusion
Vesicles move towards and fuse with presynaptic membrane
Release the neurotransmitter via exocytosis
Neurotransmitter diffuses across the synaptic cleft
Binding to receptor on post synaptic membrane
Sodium ion channels open and sodium ions enter
Why do cross bridges between actin and myosin remain firmly bound after death and lead to rigor mortis
Respiration stops
No more ATP produced
ATP needed to break the actin and myosin cross bridges
Describe the role of phosphocreatine
Provides a phosphate
Phosphorylating ADP
To produce ATP
Describe fast twitch muscle fibres
Used for rapid and brief and powerful contractions
Phosphocreatine used up rapidly during contraction to make ATP
Anaerobic respiration involved
ATP used to reform phosphocreatine
Lots of phosphocreatine in fast muscle fibres
Describe the role of calcium ions in the contraction of a sarcomere
Binds to binding site on troponin and causes tropomyosin to move
Exposing myosin head binding sites on actin
Allowing myosin head to bind to actin and form a crossbridge
Activates ATP hydrolase to hydrolyse ATP and provide energy needed for power stroke
Use of ATP other than in power stroke and recovery stroke
Active transport of calcium ions back into the sarcoplasmic reticulum
A muscle fibre can only store enough ATP to sustain muscle contraction for how long
3 to 4 seconds
How long does regeneration of ATP by anaerobic respiration take
10 seconds
This is too long in fight or flight instances
Even longer if aerobic
Is phosphocreatine a source of ATP
No
Source of Pi
Which is used to create ATP from ADP and Pi
What is phosphocreatine
A molecule stored in fast twitch muscle fibres
That can donate a Pi to phosphorylate ADP and produce ATP in the short term
Replenished during relaxation
Slow twitch muscle fibres
Slow sustained contractions over long periods of time with a slower rate of contraction
Lots found in legs and those involved in maintaining posture
How are slow twitch muscle fibres adapted/specialised
Use aerobic respiration to regenerate ATP so have many large mitochondria and some just under the sarcolemma to provide the ATP needed for active transport of calcium ions, and some deep between the myofibrils
High concentrations of myoglobin act as oxygen stores and give the slow twitch muscle fibres their red colour
Very closely associated with large number of capillaries to provide a good oxygen supply to increase amount of oxygen for oxidative phosphorylation to produce lots of ATP for muscle contraction
Less extensive sarcoplasmic reticulum since less calcium ions required at any one time
Less glycogen as glucose broken down fully by aerobic respiration
How are fast twitch muscle fibres adapted/specialised
To use PC-ATP anaerobic respiration energy systems to regenerate ATP so have fewer smaller mitochondria
Low myoglobin concentration since primary energy systems are anaerobic
Fewer capillaries associated with fibres
Extensive sarcoplasmic reticulum since more calcium ions required at one time for rapid, intense contraction
More glycogen as more glucose required as anaerobic respiration yields less ATP per glucose
Key points to discuss when comparing slow and fast twitch (9)
Colour Contraction speed Activity Duration Fatigue Power Storage Mitochondria Sarcoplasmic reticulum
SMS CDC PAF
Similarities between slow and fast twitch
Both follow sliding filament theory
Both use ATP hydrolase
Both produce ATP
Both allow for shortening of sarcomere
Compare colour for slow and fast twitch
Slow; Red due to oxidative phosphorylation and myoglobin as an oxygen store
Fast; White due to less oxygen and myoglobin
Compare duration for slow and fast twitch
Slow; Longer, more energy provided due to oxidative phosphorylation
Fast; Shorter, cannot be sustained for a long time
Compare conduction speed for slow and fast twitch
Slow; Slow
Fast; Fast
Compare storage for slow and fast twitch
Slow; Triglycerides
Fast; ATP, phosphocreatine, glycogen
Compare Mitochondria for slow and fast twitch fibres
Slow; more, longer
Fast; less, shorter
Compare sarcoplasmic reticulum for slow and fast twitch fibres
Slow; Smaller since less calcium ions needed at any one time
Fast; extensive since more calcium ions required at one time for rapid intense contraction
Compare power for slow and fast twitch
Slow; stronger, more ATP means more energy to contract all at the same time
Fast; weaker, less ATP means less energy and not enough power to contract all at the same time
Compare activity for slow and fast fibres
Slow; aerobic respiration
Fast; anaerobic respiration
Compare fatigue for slow and fast twitch fibres
Slow; resistant due to enough energy to contract for a long time in aerobic respiration without anaerobic to produce lactate
Fast; easily fatigue due to anaerobic respiration producing lots of lactate
Why do both slow and fast need ATP
To break the cross bridges between actin and myosin
To be hydrolysed to provide the energy needed for the power stroke
To actively transport calcium ions back into the sarcoplasmic reticulum
What is the role of ATP in myofibril contraction
Breaks actin and myosin cross bridge
Provides energy to move the myosin head in the power stroke
Role of tropomyosin in muscle contraction
Moves out of the way when calcium ions bind to troponin
Allowing the myosin head to bind to actin and form a cross bridge
Role of myosin in muscle contraction
Myosin head binds to actin and moves/bends to pull actin past it in power stroke
Myosin detaches from actin and retest/moves further along actin
Explain the banding pattern of a single sarcomere
Light band where there is only actin
H zone where there is overlap so darkest
Dark band where only myosin
Describe the advantage of the Bohr effect in intense excercise
Increased dissociation of oxygen
For aerobic respiration at the tissues and muscle cells
So anaerobic respiration is delayed
And less lactate so less muscle fatigue
Why does converting lactate to pyruvate allow the continuous production of ATP by anaerobic respiration
Regenerates NAD (Oxidises reduced NADP) So glycolysis can continue and ATP can still be produced
Slow twitch blood
Rich blood supply
Many mitochondria
Large store of myoglobin
Where is phospbocreatine found
Fast twitch
