6B Muscle Contraction Flashcards
How is skeletal muscle attached to bones
by tendons
What attaches bones to other bones
Ligaments
What are muscles that work together to move a bone called
Antagonist pairs
What is a contracting muscle called
agonist
What is a relaxed muscle called
antagonist
What happens when the bicep contracts
triceps relax this pulls the bone so your arm bends at the elbow
The biceps is the agonist and the triceps is the antagonist
What happens when the triceps contracts
biceps relax this pulls the bone so your arm straightens at the elbow
The triceps is the agonist and the biceps is the antagonist
What are muscle cells made up of
muscle fibres
What is the cell membrane of muscle cells called
the sarcolemma
What is the cytoplasm of muscle cells called
sarcoplasm
What are transverse tubules
folds of the sarcolemma that stick into the sarcoplasm
What is the function of transverse tubules
To spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibres
What is the sarcoplasmic reticulum
a network of internal membranes that run through the sarcoplasm
What is function of the sarcoplasmic reticulum
It stores are releases calcium ions that are needed for muscle contraction
What organelle does muscle fibres contain
myofibrils which are specialised for muscle contraction and mitochondria which provide ATP for the muscle contraction
What are thick myofibrils made from
myosin
What are thin myofibrils made from
actin
Define multinucleate
Has many nuclei
What do dark A bands in a myofibril contain
thick myosin filaments and some thin actin filaments which overlap
What do light I bands in a myofibril contain
thin actin filaments
What is a myofibril made up of
many sarcomeres
Describe the sliding filament theory
thick myosin filaments and some thin actin filaments slide over each other to make the sarcomeres contract the simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract
Sarcomeres return to their original length as the muscle relaxes
Describe the structure of myosin filaments
They have hinged globular heads so that they can move back and forth and each head has a binding site for actin and one for ATP
What are the binding sites on actin filaments called
actin-myosin binding sites
What protein is found between actin filaments
tropomyosin
In a resting muscle what happens to the actin-myosin binding sites
It is blocked by tropomyosin so the myosin head can’t bind to the actin-myosin binding site on the actin filament so myofilaments can’t slide past each other
How is the sarcolemma depolarised
by an action potential the depolarisation spreads down the t tubules to the sarcoplasmic reticulum which causes it to release stored calcium ions into the sarcoplasm
Where do the calcium ions from the sarcoplasmic reticulum bind to
They bind to a protein attached to tropomyosin causing the protein to change shape
This pulls the attached tropomyosin out of the actin myosin filament on the actin filament this exposes the binding site which allows the myosin head to bind
What is the bond called when a myosin head binds to the actin filament
actin-myosin cross bridge
Which enzyme does calcium ions activate
ATP hydrolase
What does the energy released from ATP in muscle contraction cause the myosin head to do
It causes it to bend, which pulls the actin filament along
What provides the energy to break the actin-myosin cross bridge
ATP
What happens after the actin-myosin cross bridge is broken
the myosin head detaches from the actin filament after its moved and then reattaches to a different binding site further along the actin filament and a new actin-myosin cross bridge is formed the cycle continues as long as calcium ions are present
What happens when many cross bridges form and break very rapidly
the actin filament is pulled along, shortening the sarcomere and causing the muscle to contract
What happens to calcium ions when the muscle stops being stimulated
calcium ions leave their binding sites and are moved by active transport back into the sarcoplasmic reticulum
This causes tropomyosin to move back so the block the actin myosin sites again
Muscles aren’t contracted so no myosin heads are attached to actin filaments
The actin filaments slide back to their relaxed position which lengths the sarcomere
What type of exercise is aerobic respiration good for
Most ATP is generated by oxidative phosphorylation in the mitochondria
It’s only works when there is oxygen so it is good for long periods of low intensity exercise
What type of exercise is anaerobic respiration good for
ATP is made rapidly by glycolysis and the end product is pyruvate which is converted to lactate by lactate fermentation
Lactate can build up quickly and cause muscle fatigue
so anaerobic respiration is good for short periods of hard exercise
What type of exercise is the ATP phosphocreatine used for
ATP is made by phosphorylating ADP
Pcr is stored in cells inside cells and the ATP-PCr system generates ATP very quickly
Pcr runs out very quickly so is used during short burst of vigorous exercise
The ATP-PCr system is anaerobic
Describe the properties of slow twitch muscle fibres
Muscles fibres that contract slowly
Muscle used for posture
Good for endurance activities
Can work for a long time without getting tired
Energy is released slowly through aerobic respiration lots of mitochondria and blood vessels supply the muscles with oxygen
Reddish in colour as they are rich in myoglobin
Describe the properties of fast twitch muscle fibres
Muscles fibres that contract very quickly
Muscle used for fast movement
Good for short bursts of speed and power
Get tired very quickly
Energy is released slowly through anaerobic respiration there are mitochondria or blood vessels
Whitish in colour as they don’t contain much myoglobin
