Skeletal Muscles (A Level only) (AQA A Level Biology): Flashcards
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- FrontAntagonistic Muscles
Define an antagonistic pair of muscles.
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Define an antagonistic pair of muscles.
A pair of muscles in which one muscle pulls a bone in one direction, and the other muscle pulls the bone in the opposite direction.
Why do skeletal muscles often act in antagonistic pairs?
Because muscles can only pull, and cannot push.
A second muscle is therefore needed to pull the bone back in the opposite direction.
What is the role of a tendon?
A tendon connects a muscle to a bone.
Tendons do not stretch when a muscle contracts, so the pulling force is transmitted to the bone.
How do skeletal muscles bring about movement of the skeleton?
They exert a pulling force on the rigid, incompressible skeleton.
Muscles are connected to bones by tendons, which do not stretch, so contraction pulls on the bone.
What happens to the biceps and triceps to raise the lower arm?
The biceps contracts and the triceps relaxes.
The bone of the lower arm is pulled upwards and the arm bends at the elbow.
What happens to the biceps and triceps to straighten the arm?
The triceps contracts and the biceps relaxes.
The bone of the lower arm is pulled down and the arm straightens.
True or False?
Muscles are able to both push and pull on bones.
False.
Muscles can only pull, not push, which is why they act in antagonistic pairs.
Muscles are connected to bones by , which do not when a muscle contracts.
Muscles are connected to bones by tendons, which do not stretch when a muscle contracts.
In the arm, the biceps and form an antagonistic pair because muscles can only a bone.
In the arm, the biceps and triceps form an antagonistic pair because muscles can only pull a bone.
By what two other names is skeletal muscle known?
Striated (or striped) muscle.
It is the muscle that contracts to move the skeleton.
In a muscle fibre, what is the sarcolemma?
The cell surface membrane of a muscle fibre.
It has deep tube-like projections called T-tubules that fold in from its surface.
In a muscle fibre, what is the sarcoplasm?
The cytoplasm of a muscle fibre.
It contains myofibrils and many mitochondria.
In a muscle fibre, what is the sarcoplasmic reticulum?
The endoplasmic reticulum of a muscle fibre.
What is a myofibril?
A long, rod-like structure made of protein filaments found in the sarcoplasm.
Myofibrils are made of the contractile proteins myosin and actin.
Name the thick and thin protein filaments found in a myofibril.
Myosin = thick filaments.
Actin = thin filaments.
Give two features of a muscle fibre.
Each muscle fibre is an elongated cell that contains many nuclei.
The sarcoplasm contains many mitochondria that generate ATP for muscle contraction.
What is a sarcomere?
A section of a myofibril that shortens during muscle contraction as myosin and actin filaments slide past each other.
What is found at the Z-line and the M-line of a sarcomere?
The Z-line is the boundary between sarcomeres, where actin filaments attach.
The M-line is the central point of the sarcomere, where myosin filaments attach.
Which bands of the sarcomere contain only actin and which contain only myosin?
The I band contains only actin filaments.
The H band contains only myosin filaments.
What happens to the A band, H band and I band during muscle contraction?
The A band stays the same length.
The H band becomes shorter.
The I band becomes shorter.
True or False?
The A band changes length when a muscle contracts.
False.
The myosin filaments do not change in length, so the A band remains the same size whether the muscle is contracted or relaxed.
In a muscle fibre, the cell surface membrane is called the and the cytoplasm is called the .
In a muscle fibre, the cell surface membrane is called the sarcolemma and the cytoplasm is called the sarcoplasm.
What type of microscope is used to examine pre-prepared slides of skeletal muscle in a school laboratory?
An optical (light) microscope.
Which features of skeletal muscle are visible under an optical microscope?
Banding.
Nuclei.
Why can an optical microscope not show the detailed structure of muscle fibres?
Its resolution is too low to see the details of muscle structure.
Which type of microscope is used to view the detailed structure of myofibrils, and why?
An electron microscope.
It has a higher resolution, revealing detail not visible with an optical microscope.
When viewed with an electron microscope, which band do the light bands correspond to?
The I bands.
When viewed with an electron microscope, which band do the dark bands correspond to?
The A bands.
What produces the characteristic striped appearance of skeletal muscle?
The dark bands in skeletal muscle produce the characteristic striped appearance.
True or False?
Under an electron microscope, the dark bands correspond to the I bands.
False.
The dark bands correspond to the A bands; the light bands correspond to the I bands.
Under an electron microscope, the light bands correspond to the bands and the dark bands correspond to the bands.
Under an electron microscope, the light bands correspond to the I bands and the dark bands correspond to the A bands.
Dark lines seen with an electron microscope occur at each of the sarcomere.
Dark lines seen with an electron microscope occur at each Z-line of the sarcomere.
Describe the sliding filament theory of muscle contraction.
During muscle contraction, the actin and myosin filaments slide over each other, causing the sarcomeres to shorten.
What is the role of tropomyosin in a relaxed muscle?
Tropomyosin blocks the actin-myosin binding sites on the actin filaments when the muscle is relaxed.
What is the role of calcium ions at the start of muscle contraction?
Calcium ions are released from the sarcoplasmic reticulum when an action potential arrives.
They cause tropomyosin to change position, exposing the actin-myosin binding sites.
What is a cross-bridge in muscle contraction?
The bond formed when myosin heads bind to actin filaments.
Describe the power stroke in muscle contraction.
The myosin heads bend, releasing ADP and inorganic phosphate.
This pulls the actin filaments towards the centre of the sarcomere.
What causes the myosin heads to detach from the actin filaments?
ATP binds to the myosin heads, causing them to release from actin.
What is the role of ATP hydrolase after the myosin heads detach?
It hydrolyses the ATP, providing the energy that allows the myosin heads to reset to their original positions.
The heads can then bind to new binding sites and the process repeats.
What happens in a muscle fibre when it is no longer stimulated by nerve impulses?
Calcium ions are taken back up into the sarcoplasmic reticulum.
The actin-myosin binding sites are blocked, so myosin can no longer bind to actin.
The filaments are pulled apart by the action of an antagonistic muscle.
By what process do calcium ions return to the sarcoplasmic reticulum after contraction?
Active transport.
True or False?
The bending of the myosin heads is a direct result of ATP hydrolysis.
False.
The bending (power stroke) occurs spontaneously with the release of ADP and Pi.
ATP hydrolysis instead provides the energy to reset the myosin heads.
Give three sources of the ATP needed for muscle contraction.
Aerobic respiration.
Anaerobic respiration.
Phosphocreatine.
When an action potential arrives, ions are released from the reticulum.
When an action potential arrives, calcium ions are released from the sarcoplasmic reticulum.
Phosphocreatine allows the rapid production of ATP: ADP + phosphocreatine → + .
Phosphocreatine allows the rapid production of ATP: ADP + phosphocreatine → ATP + creatine.
Name the two types of muscle fibre found in skeletal muscle.
Fast muscle fibres.
Slow muscle fibres.
Which type of respiration supplies most of the ATP for fast muscle fibres, and for slow muscle fibres?
Fast fibres rely mostly on anaerobic respiration.
Slow fibres rely mostly on aerobic respiration.
Why do fast muscle fibres fatigue quickly?
Because of lactate production from anaerobic respiration.
Compare the colour of fast and slow muscle fibres.
Fast fibres are pale in colour.
Slow fibres are darker in colour.
What type of activity are slow muscle fibres suited to, and where are they found in humans?
Sustained, low-intensity activities.
They are found in human back and leg muscles.
What type of activity are fast muscle fibres suited to?
Short bursts of high-intensity activity, e.g. the human biceps and triceps or eyelid muscles.
Compare the mitochondria of fast and slow muscle fibres.
Fast fibres have fewer, smaller mitochondria.
Slow fibres have many, large mitochondria.
Why do slow muscle fibres have a dense capillary network and a high myoglobin content?
Because they rely on aerobic respiration, which creates a high demand for oxygen.
Compare the store of calcium ions in the sarcoplasmic reticulum of fast and slow muscle fibres.
Fast fibres have a large store of calcium ions.
Slow fibres have a small store of calcium ions.
Why do fast muscle fibres contain fewer mitochondria?
Because they rely mainly on anaerobic respiration.
Aerobic respiration provides energy too slowly for their fast rate of contraction.
True or False?
Slow muscle fibres have large glycogen and phosphocreatine stores.
False.
Fast fibres have large glycogen and phosphocreatine stores; slow fibres have small stores.
Fast fibres are pale and rely on respiration, whereas slow fibres are darker and rely on respiration.
Fast fibres are pale and rely on anaerobic respiration, whereas slow fibres are darker and rely on aerobic respiration.
Give two reasons why repeated contraction may cause muscle fatigue.
Production of lactate during anaerobic respiration.
A decrease in the availability of calcium ions after repeated contractions.
What apparatus can be used to investigate muscle fatigue in humans?
A hand grip strengthener.
A stopwatch.
Willing human subjects.
Outline the method for investigating muscle fatigue using a hand grip strengthener.
Squeeze the hand grip strengthener as many times as possible over 20 seconds and record the number of successful squeezes.
Rest for 10 seconds.
Repeat these steps several more times, then repeat with other human subjects.
What result would you expect from a muscle fatigue investigation using a hand grip strengthener?
The number of successful squeezes decreases over time.
Why does fatigue occur during the hand grip strengthener investigation?
The same hand muscles are being used repeatedly.
This reduces the ability of these muscles to contract.
Give two limitations of the hand grip strengthener investigation into muscle fatigue.
It only looks at fatigue in hand muscles, and other skeletal muscles may fatigue at different rates.
The exercise intensity may not be high enough to cause fatigue in some individuals.
True or False?
The hand grip strengthener investigation measures fatigue in all skeletal muscle groups.
False.
It only looks at muscle fatigue in the hand muscles; other muscle groups may fatigue at different rates.
Repeated muscle contraction can cause fatigue due to the production of during anaerobic respiration.
Repeated muscle contraction can cause fatigue due to the production of lactate during anaerobic respiration.
Muscle fatigue may also result from a decrease in the availability of ions after repeated contractions.
Muscle fatigue may also result from a decrease in the availability of calcium ions after repeated contractions.
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