Muscles Flashcards
What do muscles act as against an incompressible skeleton (1)
Antagonist pairs
How are skeletal muscles attached to the bone (1)
By tendons
What is a muscle fibre? (3)
Highly specialised
Long thin cells containing several nuclei
Contain a large number of myofibrils
Describe the structure of skeletal muscles (7)
Composed of many muscle fibres bound together by connective tissue
Each muscle fibre is surrounded by a thin cell membrane called a sarcolemma
The cell contains cytoplasm called sarcoplasm
Muscle fibres contain a large number of myofibrils which run parallel to each other throughout the full length of the cell
Each myofibril is surrounded by sarcoplasmic reticulum
Each myofibril is made up of myofilaments, these are divided into thick (myosin) and thin myofilaments (actin)
These myofilaments are arranged into sarcomeres
What does the sarcoplasm contain? (1)
Large number of mitochondria
What are sarcomeres? (1)
Myofilaments arranged into contractile units
What are skeletal muscles often called? (1)
Striated muscles
Describe the sliding filament theory (7)
Ca2+ are released from the sarcoplasmic reticulum into sarcoplasm.
Ca2+ diffuse and bind to troponin (changes the tertiary structure) and cause tropomyosin to move exposing the myosin head binding sites on the actin filament
Myosin heads bind to actin binding sites forming cross bridges.
The myosin head “bends” pulling the actin filament a short distance (over the myosin) [POWER STROKE]
ADP & Pi are released from the Myosin head
A new ATP binds to myosin head. This breaks the cross bridge and separates it from the actin. ATP is hydrolysed to ADP and Pi by ATP hydrolase, the energy released re-cocks the myosin head. [RECOVERY STROKE]
The process repeats pulling the actin along the myosin filament a bit more each time.
Describe the role of ATP in muscle contraction (3)
Releases energy for power stroke and recovery stroke
Breaks cross bridge between actin-myosin
Provides energy for active transport of Ca2+ back into sarcoplasmic reticulum
Describe the role of calcium ions in muscle contraction (2)
Binds to troponin - movement of tropomyosin to reveal myosin binding sites on actin
Activates ATP hydrolase
Describe the role of phosphocreatine in muscle contraction (3)
Energy released from hydrolysis of ATP is used in the phosphorylation of ATP
Phosphocreatine provides phosphate to make ATP
Which can then be used in muscle contraction
Where are slow twitch fibres found? (2)
Muscles of the leg
Those involved in maintaining posture
Describe features of slow twitch fibres (9)
Specialised to use aerobic respiration energy system to regenerate ATP. Many large mitochondria to produce ATP
High concentration of myoglobin - acts as oxygen store
Very closely associated with a large number of capillaries, to provide a good oxygen supply.
Less extensive sarcoplasmic reticulum as less calcium ions required at one time.
Less glycogen as glucose broken down fully via aerobic respiration
Smaller in diameter
Less/no stored of phosphocreatine
Describe features of fast twitch muscle fibres (9)
Specialised to use anaerobic respiration energy systems to regenerate ATP. So have fewer, smaller mitochondria.
Low concentration of myoglobin - as primary energy systems are anaerobic.
Fewer capillaries associated with fibres.
Extensive sarcoplasmic reticulum as 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.
High concentration of enzymes involved in anaerobic respiration which provide ATP rapidly
Larger in diameter
Stores of phosphocreatine
Thicker and more numerous myofilaments
Contrast fast and slow twitch muscle fibres (6)
Slow twitch:
Contract slower
Less powerful contraction over a long period
Suitable sports - in marathons
Location - In human calf due to maintaining posture
Aerobic respiration
Slower fatigue
Fast twitch:
Contract rapidly
More powerful contraction over a long period
Suitable sports - intense exercise (sprint, weight lifting)
Location - short bursts of intense activity e.g. biceps, fine motor movements (eye, hand)
Anaerobic respiration
Faster fatigue
People who have McArdle’s disease produce less ATP than healthy people. As a result, they are not able to maintain strong muscle contraction during exercise. Use your knowledge of the sliding filament theory to suggest why. (4)
(Idea ATP is needed for:)
Attachment/cross bridges between actin and myosin.
‘Power stroke’ / movement of myosin heads
Detachment of myosin heads
Myosin heads move back/ ‘recovery stroke’
Describe the part played by tropomyosin & myosin in myofibril contraction (5)
Tropomyosin:
Moves out of the way when calcium ions bind
Allowing myosin to bind (to actin) / cross bridge formation
Myosin:
Head (of myosin) binds to actin and moves/pulls actin
(Myosin) detaches from actin and re-sets / moves further along (actin)
This uses ATP
The mitochondria in muscles contain many cristae.
Explain the advantage of this (2)
Larger surface area for oxidative phosphorylation
Provide ATP for contraction
Explain why increased cardiac output is an advantage during exercise (5)
In exercise more energy release for aerobic respiration
Higher cardiac output - Increases O2 supply (to muscles)
Increases glucose supply (to muscles)
Increases CO2 removal (from muscles) / lactate removal
Increases heat removal (from muscles) / for cooling
Explain the importance of ATP hydrolase during muscle contraction (2)
Hydrolyses ATP yielding energy
Used to form / break actomyosin bridges
Muscle contraction requires ATP
What are the advantages of using aerobic rather than anaerobic respiration to provide ATP in a long-distance race? (4)
Aerobic respiration releases more energy /produces more ATP
Little/no lactate produced
Avoids muscle fatigue
CO2 easily removed from the body / CO2 removed by breathing
A muscle fibre contracts when it is stimulated by a motor neuron.
Describe how transmission
occurs across the synapse between a motor neuron and a muscle fibre (7)
Ca2+ channel proteins open Ca2+ ions enter (neuron) by facilitated diffusion
Vesicles fuse with presynaptic membrane
Release of acetylcholine
Diffusion (of transmitter) across gap / cleft
(Transmitter) binds to receptors in postsynaptic membrane
Na+ channels open / Na+ ions enter (postsynaptic side)
After death, cross bridges between actin and myosin remain firmly bound resulting in rigor mortis. Explain what causes the cross bridges to remain firmly bound (3)
Respiration stops
No ATP produced
ATP required for separation of actin and myosin/cross bridges
Describe the role of calcium ions in the contraction of a sarcomere (4)
Interact with/move/touch tropomyosin
To reveal binding sites on actin; (not active sites)
Allowing myosin (heads) to bind to actinomyosin formed
Activate ATP hydrolase / energy released from ATP
Describe fast twitch muscle fibres (4)
Used for rapid/strong contractions
Phosphocreatine used up rapidly during contraction/to make ATP
Anaerobic respiration involved
ATP used to reform phosphocreatine
Lots of phosphocreatine in fast fibres
Describe the role of phosphocreatine (2)
Provides phosphate / phosphorylates
To synthesise ATP
Allows regenration of ATP without respiration
Name the 3 types of muscles and where they are located in the body (3)
Cardiac: found in heart
Smooth: found in walls of blood vessels and small intestines
Skeletal: attached to incompressible skeleton by tendons
Describe the ultra structure of a myofibril (4)
Z-line: boundary between sarcomeres
I-band: only actin (appears light under optical microscope)
H-zone: only myosin
A-band: overlap of actin and myosin (appears dark under optical microscope)
State 4 pieces of evidence that support the sliding filament theory (4)
H-zone narrows
I-band narrows
Z-lines get closer (sarcomere shortens)
A-zone remains the same width (proves that myosin filaments do not shorten)
What happens during muscle relaxation? (2)
Ca2+ ions actively transported back into the sarcoplasmic reticulum
Tropomyosin once again blocks actin binding site
Describe how a student could calculate the length of one sarcomere (3)
View thin slice of muscle under optical microscope
Calibrate eyepiece graticule
Measure distance from middle of one light band to middle of another
