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