Muscles Flashcards
What is cardiac muscle?
Contracts without conscious control - only found in the heart
What is smooth muslce?
Contracts without conscious control - found in the walls of internal organs e.g. stomach, intestine, blood vessels
What is skeletal muscle?
Voluntary muscle, used to move e.g. biceps and triceps
What is skeletal muscle also known as?
Striated, Striped, Voluntary muscle
What is skeletal muscle made up of?
Long cells - called muscle fibres
What is the cell membrane of the muscle fibre called?
Sarcolemma
What are transverse (T) tubules?
Where parts of the sarcolemma fold inwards all across the muscle fibre - they stick into the sarcoplasm.
What is the sarcoplasm?
The muscle fibres cytoplasm.
What do T tubules help do?
They help spread electrical impulses throughout the sarcoplasm. This is so that they reach all parts of the muscle fibre.
What is the sarcoplasmic reticulum?
It is a network of internal membranes which run through the sarcoplasm.
What does the sarcoplasmic reticulum do?
It stores and releases calcium ions - needed for muscle contraction.
What do muscle fibres have lots of and why?
Mitchondria - to provide the ATP needed for muscle contraction.
What are multinucleate?
Muscle fibres
Muscle fibres have lots of long cylindrical ORGANELLES… what are they called?
Myofibrils
What are myofibrils made up of?
proteins
Myofibrils are highly specialised for what?
Contraction
What do myofibrils contain?
Bundles of thick and thin myofilaments
What do the myofilaments do to make muscles contract?
The myofilaments move past each other
What are the thick myofilaments made up of?
The protein - myosin
What are the thin myofilaments made up of?
The protein - actin
What can you see when looking at a myofibril under an electron microscope?
A pattern of alternating dark and light bands.
What do the dark bands show in a myofibril - under an electron microscope?
The thick myosin filaments + some overlapping thin actin filaments
These are called A-bands
dArk bands
What do the light bands show in a myofibril - under an electron microscope?
Contain only the thin actin filaments
These are called I-bands
What is a myofibril made up of?
Many short units called - sarcomeres
What marks the end of each sarcomere?
Z-line
What is the middle of each sarcomere called?
M-line
What is the H-zone?
Near the M-line, but only contains myosin filaments
What are the A-bands?
thick myosin filaments + some overlapping thin actin filaments
What are the I-bands?
Contains only the thin actin filaments
What changes when the sarcomere is contracting?
The I-band gets shorter
The H-zone gets shorter
What is the only thing that stays the same when the sacromere contracts?
The A-band
What is the sliding filament theory?
Where actin and myosin filaments slide over one another to make the sacromere contract
How does the sliding filament theory result in muscle contraction?
The sacromeres contract –> the myofibrils contract –> the muscle fibres contract
What happens to the sacromere when it relaxes?
It returns back to its original length.
What do ligaments connect?
Bone to bone
What do tendons connect?
Skeletal muscle to bone
How do a pair of muscles act?
In antagonistic pairs against an incompressible skeleton.
Describe the role of calcium ions in the contraction of a myofibril:
Ca ions diffuse from the sarcoplasmic reticulum into the myofibrils
Ca ions cause the movement of tropomyosin
This movement exposes the binding site on the actin
Myosin heads attach to binding site on actin
An actin-myosin cross-bridge forms
DESCRIBE the role of ATP in the contraction of a myofibril:
Hydrolysis of ATP (on myosin heads) causes myosin heads to bend
Pulling actin molecules
Attachment of a new ATP molecule to each myosin head causes myosin heads to detach from actin sites.
WHAT is the role of ATP in myofibril contraction?
Provides energy to move myosin heads
Reaction with ATP breaks actin-myosin bridge and allows binding of myosin to actin.
A fall in pH leads to a reduction in the ability of calcium ions to stimulate muscle contraction - how?
low pH changes shape of Ca2+ receptors, so fewer Ca2+ bind to tropomyosin, so fewer tropomyosin molecules move away, fewer binding sites on actin revealed, fewer myosin heads can bind and fewer actin-myosin cross bridges form.
How is ATP a suitable energy sources for cells to use?
It phosphorylates other compounds, making them more reactive
It can be rapidly re-synthesised
Releases energy instaneously
Releases relatviely small amounts of energy
ATP is not lost from cells
What are the 3 sources of energy for muscle contraction?
Aerobic respiration
Anaerobic respiration
ATP - PCr system
What does PCr stand for?
Phosphocreatine
How does the ATP-PCr system provide energy for muscle contraction?
ADP is phosphorylated using a phosphate group from PCr. The system geenrates ATP very quickly.
The system is anaerobic and it’s alactic
Where is PCr stored?
insides cells
When is the ATP-PCr system used?
During short bursts of vigorous exercise as PCr runs out very quickly
What does alactic meaning?
Does not form lactate
What does PCr get broken down into?
Creatinine
Where can creatinine be removed from and to where?
From blood via kidneys
How does aerobic repiration provide energy for muscle contraction?
Most ATP is generated via oxidative phsophorylation (in mitochondria)
Long periods - low intensity
How does anaerobic repiration provide energy for muscle contraction?
ATP made rapidly by glycolysis. End product is pyruvate –> converted into lactate (by lactate fermentation)
Lactate quickly builds up on muscles causing fatigue - short periods/ high intensity
Why is converting pyruvate to lactate essential for the continued production of ATP (during anaerobic respiration)?
Regenrates NAD
So that glycolysis can continue
What is myoglobin?
A single chain protein
It has a high affinity for oxygen and can combine at very low partical pressures
What is a slow twitch muscle fibre?
Found in muscles that carry out endurance exercise - adapted to carry out aerobic respiration
How are slow twitch muscle adapted to aerobic respiration?
They are high in myoglobin
What colour are slow and fast twitch muscle fibres?
Slow - red
Fast - pale
What is a fast twitch muscle fibre?
contract rapidly/powerfully for short periods. useful for intense exercise + adapted for anaerobic respiration (LOW in myoglobin)
