Muscles- Paper 2 Flashcards
Describe what a smooth muscle is
They contract without conscious control
Found in walls of internal organs (apart from the heart) such as stomach, intestine and blood vessels. They can contract to increase or decrease lumen
Describe what a cardiac muscle is
Cardiac muscle contracts without conscious control (myogenic) which is only found within the heart
Describe what a skeletal muscle is
they are strained, striped or voluntary
Type of muscle used in locomotion (movement)
Found in biceps and triceps which move the lower arm antagonistically
How does a skeletal muscle work
It is attached to bone by tendons
Contracts in response to the release of acetylcholine from a motor neurone, bringing out the ,movement of a bone at joint
Muscles can only pull, so opposing muscle groups are needed, which pull in opposite directions at a joint.
One contracts and one relaxes
Contracting muscle= agonist and relaxing muscle= antagonist
Describe the structure of a skeletal muscle
Composed of many muscle fibres bound together by connective tissue
Muscle fibres are highly specialised with long thin cells containing several nuclei
Each muscle fibre surrounded by thin cell membrane called sarcolemma and its nuclei are just beneath
Cell contains sarcoplasm which contain a large number of mitochondria
Also contain a large number of myofibrils which run parallel to eachother
Each myofibril surrounded by sarcoplasmic reticulum, made up of myofilaments which are divided into thick (myosin) and thin myofilaments (actin)
Myofilaments arranged into contractile unties called sarcomeres
Where are actin and myosin found on myofibrils
Actin- anchored to Z discs
Myosin- anchored to M line
Which bands appear light and which appear dark
dark- A band
Light- I band
Describe how the sliding filament theory contracts and shortens specific bands
Each sarcomere shortens, bringing the Z lines closer together, as actin is pulled over myosin filaments increasing the amount they overall
Describe how the bands shorten and contract or stay the same during muscle contraction
A band- stays the same
I band- shortens
H zone- shortens
Z discs- get closer together
Sarcomere- shortens
Describe the sliding filament theory (7 key points) when a muscle fibre is excited by a motor neurone
Ca2+ are released from the sarcoplasmic reticulum into sarcoplasm
Ca2+ diffuse and cause tropomyosin to move exposing the myosin head binding sites on the actin filament
Myosin head binds to actin binding site forming actinomyosin cross bridges
Myosin head bends, pulling the actin filament a short distance over the myosin- power stroke
ADP and Pi are released from myosin head, breaking the cross bridge and separated it from the actin. ATP is hydrolysed to ADP and Pi by ATP hydrolyse, the energy released re-cocks the myosin head- recovery stroke
Process repeats pulling the actin along the myosin’s filament a bit more each time
Explain the role of Ca2+ after the sliding filament theory has occurred
Ca2+ ions are actively transported back into sarcoplasmic ER
Ca2+ also activate ATP hydrolyse
What is the role of ATP in the sliding filament theory
ATP releases energy and changes the shape of myosin head
What is ATP required for in muscles
- The sliding of filaments during contraction
- The active transport of Ca2+ ions into the sarcoplasmic reticulum.
Explain how phosphocreatine is used
Muscle fibres store it- it is a molecule that can donate a phosphate top ADP, regenerating ATP in short term
It can be regenerated using ATP which is supplied via aerobic respiration
Energy released not used directly- energy released is used in the phosphorylation of ATP, which can then be used in muscle contraction
What are slow twitch muscle fibres and what is their role
Produce slow sustained contractions over long time periods but have a slower rate of contraction
Muscles with high proportions of slow twitch fibres are slow to fatigue, large numbers of this fibre are found in the muscles of the legs and those in maintaining posture
Explain the process of slow twitch fibres
Specialised to use aerobic respiration energy system to regenerate ATP. They have many large mitochondria- some just under sarcolemma to provide ATP for active transport, and some deep between the myofibrils
High concentrations of myoglobin acts as an oxygen store
Very closely associated with large numbers 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 for aerobic respiration
Describe how fast twitch muscle fibres work
Produces a rapid, strong contractions as have a faster speed of contraction but only sustained over short tine periods. Muscles contain many of this fibre type are fast to fatigue caused by a build up of lactate.
Describe hope fast twitch muscles fibres work, the process behind it
Specialised PC-ATP anaerobic respiration energy systems to regenerate ATP
So have fewer, smaller mitochondria
Low concentrations 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 for anaerobic respiration yields less ATP per glucose molecule
People who have McArdle’s disease produce less ATP than healthy people. Sam’s a result, they are not able to maintain strong muscle contraction during exercise
Use your knowledge of the sliding filament theory to suggest why
Attachment/ cross bridges form between actin and myosin
Power stroke/ movement of myosin heads
Detachment of myosin heads
My spin heads move back to original position/ recovery stroke
Describe the part played by tropomyosin and myosin in myofibril contraction
Tropomyosin:
Moves out of the way when calcium ions bind
Allowing myosin head to bind to actin filament and cross bridges to form
Myosin:
head of myosin binds to actin and moves actin past
Myosin detaches from actin and re-sets
This uses ATP
The mitochondria in muscles contain many cristae
Explain the advantage for this
Larger surface area for electron carrier system/ oxidative phosphorylation
Provides ATP / energy for contraction
Explain why increased cardiac output is an advantage during excercise
In exercise more energy released
Higher cardiac output- increases O2 supply to muscles
Increases glucose supply to muscles
Increase CO2 removal from muscles/ lactate removal
Increases heat removal from muscles for cooling
Explain the importance of ATP hydrolyse during muscle contraction
Hydrolyses ATP yielding energy
Used to form/ break actinomyosin bridges
Muscle contraction requires ATP
What are the advantages of using aerobic rather than anaerobic to provide ATP in a long-distance race
Aerobic respiration releases more energy /produce more ATP
Little/no lactate produced
Avoids cramp and fatigue
CO2 easily removed from the body
A muscle fibre contracts when it is stimulated by a motor neurone
Describe how transmission occurs across the synapse between a motor neuron and a muscle fibre
Ca2+ channel proteins open
Ca2+ ions enter by facilitated diffusion
Vesicles move towards presynaptic membrane
Release/exocytosis of transmitter substance
Diffusion of transmitter across gap/cleft
Transmitter binds to receptors in postsynaptic membrane
Na+ channels open and Na+ enter
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
Respiration stops
No ATP produced
ATP required for separation of actin and myosin
Describe the role of calcium ions in the contraction of sarcomere
Interact with tropomyosin
To reveal binding sites on actin
Allowing myosin heads to bind
Activate ATP hydrolyse
Describe fast twitch muscle fibres
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
Provides phosphate
To synthesise ATP
