muscle contraction + junctions Flashcards
What is a neuromuscular junction? (2)
Synapse;
Between a motor neurone and a muscle cell
What is a motor unit? (2)
A motor unit is all the muscle fibres supplied by a single motor neurone;
These fibres act as a single unit
What does a motor unit consist of? (2)
Motor neurone;
All the fibres it connects to
How do motor units function in different levels of force? (2)
If a strong force is needed, a large number of motor units are stimulated;
If a small force is needed, a small number of motor units are stimulated
What neurotransmitter is used at neuromuscular junctions, and where does it bind? (2)
Acetylcholine is used at neuromuscular junctions;
It binds to nicotinic cholinergic receptors on the muscle cell membrane
How does a neuromuscular junction work similarly to synapses between neurones? (2)
Depolarisation of the muscle cell causes it to contract;
If the threshold is reached, just like in a neurone synapse
What is the role of acetylcholinesterase at neuromuscular junctions? (2)
Stored in the clefts on the postsynaptic membrane;
Breaks down acetylcholine after use to prevent continuous stimulation
Why are there many neuromuscular junctions along the length of a muscle? (2)
To ensure that all muscle fibres contract simultaneously;
If only one junction existed, not all fibres would contract together, and the muscle contraction would be weaker
How can chemicals or drugs affect neuromuscular junctions, and what could be the result? (4)
Chemicals or drugs can block the release of neurotransmitters or prevent them from binding to receptors.;
This prevents the action potential from being passed on, stopping muscle contraction;
If this affects the muscles involved in breathing (e.g., diaphragm);
It can be fatal as ventilation would stop and aerobic respiration couldn’t occur
What happens when acetylcholine is released at the neuromuscular junction? (2)
Acetylcholine diffuses across;
It binds to specific receptors on the sarcolemma (post-synaptic membrane)
What happens after the sarcolemma is depolarised? (2)
Depolarisation spreads along the muscle fibre;
It causes stored calcium ions to be released from the sarcoplasmic reticulum into the sarcoplasm
What is the role of calcium ions in muscle contraction? (3)
Calcium ions bind to troponin, causing it to change shape;
This pulls tropomyosin away from the actin-myosin binding site;
Exposing the site for myosin to bind
What is the actin-myosin cross bridge? (2)
The bond formed;
When the myosin head binds to the actin filament at the exposed binding site
How does ATP provide energy for muscle contraction? (3)
ATPase (activated by calcium ions) breaks down ATP into ADP + Pi;
Providing energy for the myosin head to bend and pull the actin filament along;
Shortening the sarcomere and contracting the muscle
What happens after the actin filament is pulled along? (3)
ATP provides energy to break the actin-myosin cross bridge;
Allowing the myosin head to reattach to a different binding site further along the actin filament;
This cycle continues as long as calcium ions are present
What are the roles of calcium ions (Ca²⁺) in muscle contraction? (2)
Ca²⁺ ions move tropomyosin, exposing the myosin-binding sites on actin;
Ca²⁺ ions activate ATPase to provide energy for muscle contraction
What are the roles of ATP in muscle contraction? (2)
ATP provides energy to detach the myosin head from the actin;
ATP actively transports Ca²⁺ ions back into the sarcoplasmic reticulum when the muscle relaxes
What happens when the muscle stops being stimulated? (5)
Calcium ions leave their binding sites on troponin;
They are actively transported back into the sarcoplasmic reticulum;
Troponin returns to its original shape, pulling tropomyosin back over the actin-myosin binding sites, blocking them;
No myosin heads are attached to the actin filaments, and the muscle relaxes;
The actin filaments slide back to their relaxed position, lengthening the sarcomere
How is ATP generated via aerobic respiration during exercise? (3)
ATP is generated through oxidative phosphorylation;
It only works when oxygen is present;
This is useful for long periods of low-intensity exercise, such as jogging
How is ATP generated via anaerobic respiration during exercise? (4)
ATP is produced rapidly by glycolysis, with pyruvate as the end product;
Pyruvate is converted into lactate by lactate fermentation;
Lactate buildup causes muscle fatigue;
This system is useful for short periods of high-intensity exercise, such as sprinting
How does the ATP-Creatine Phosphate (CP) system work? (4)
ATP is produced by phosphorylating ADP using a phosphate group from creatine phosphate (CP), which is stored in cells;
This system generates ATP very quickly but runs out in a few seconds;
It is useful for short bursts of very vigorous exercise, such as a tennis serve;
The ATP-CP system is anaerobic (does not require oxygen) and alactate (does not produce lactate)
