Muscle fibres + Neuromuscular junctions Flashcards
How do slow - twitch fibres contract compared to fast - twitch fibres?
They contract more slowly and generate less powerful contractions bus sustain activity for a longer period
What type of activity are slow - twitch fibres adapted for?
Endurance activities, such as long-distance running or maintaining posture
Why are slow - twitch fibres adapted for aerobic respiration?
To prevent lactic acid buildup, which would reduce efficiency during prolonged contractions
Where in the body are slow - twitch fibres more common?
In muscles that are constantly active,. such as the calf muscles for maintaining posture
What adaptations do slow - twitch fibres have for aerobic respiration?
- Large store of myoglobin (oxygen-storing protein, giving red colour)
- Rich supply of blood vessels ( delivers oxygen and glucose)
- Numerous mitochondria (produces ATP for sustained activity)
How do fast - twitch fibres contract compared to slow - twitch fibres?
They contract rapidly and produce powerful contractions, but fatigue quickly
What type of activity are fast - twitch fibres adapted for?
Short bursts of intense exercise, such as sprinting or weightlifting
Where in the body are fast - twitch fibres more common?
In muscles that require short, intense contractions such as biceps
What adaptations do fast - twitch fibres have for anaerobic respiration?
- Thicker and more numerous myosin filaments (for stronger contractions)
- High concentration of glycogen (provides energy for ATP production)
- High concentration of anaerobic respiration enzymes (produces ATP rapidly)
- Store of phosphocreatine (regenerates ATP quickly from ADP in anaerobic conditions)
What is a neuromuscular junction?
The point where a motor neurone meets a skeletal muscle fibre
What is a motor unit?
A group of muscle fibres that are all stimulated by a single motor neurone and act together
Why are there many neuromuscular junctions?
To ensure rapid and stimulaneous contraction of muscle fibres for powerful movement
What would happen if a muscle had only one neuromuscular junction?
Contraction would spread slowly across the muscle, leading to delayed and weaker movement
How does a motor unit control the force exerted by a muscle?
If a low force is needed, fewer motor units are stimulated. If there is a high force needed, then more motor units are stimulated
What happens when a nerve impulse reaches the neuromuscular junction?
Synaptic vesicles fuse with the presynaptic membrane, releasing acetylcholine into the synaptic cleft
What does acetylcholine do after being released?
It diffuses across the synapse and binds to receptors on the muscle fibre membrane (postsynaptic membrane)
How does acetylcholine affect the muscle fibre released?
It increases permeability to sodium ions (Na+), allowing them to enter rapidly and depolarise the membrane
Why must acetylcholine be broken down after transmission?
To prevent overstimulation of the muscle and allow for controlled contractions
What enzyme breaks down acetylcholine?
Acetylcholinesterase, which hydrolyses acetylcholine into choline and ethanoic acid (acetyl)
What happens to choline and ethanoic acid after acetylcholine is broken down?
They diffuse back into the presynaptic neurone and are recombined into acetylcholine using ATP from mitochondria
What are the key similarities between a neuromuscular junction and a cholinergic synapse? (4 points)
Both use:
1. Use neurotransmitters that are transported by diffusion
- Have receptors that when bound to the neurotransmitter, cause an influx of sodium ions
- Use a sodium - potassium pump to repolarise the membrane after activation
4.Use enzymes to break down the neurotransmitter after transmissions
