Muscle contraction Flashcards
what is the relationship between the CNS and Muscular movement?
The CNS (brain and spinal cord) receives sensory information and decides what kind of response is needed.
If the response needed is movement, the CNS…
sends signals along neurons to tell Skeletal muscle to contract.
What is Skeletal muscle?
Skeletal muscle (also called striated, striped or voluntary muscle) is the type of muscle you use to move, e.g the biceps and triceps move the lower arm.
What makes up Skeletal muscle?
Skeletal muscle is made up of large bundles of long cells called muscle fibres.
What is the name of the cell membrane of muscle fibre cells?
Sacrcolemma
Bits of the sarcolemma fold inwards across
the muscle fibre and stick into the sarcoplasm (a muscle cell’s cytoplasm)
When the sarcolemma folds this is called…
transverse tubules (T) tubules.
What are transverse (T) tubules useful for?
Transverse (T) tubules help to help spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibres.
A network of internal membranes called the …
sarcoplasmic reticulum runs through the sarcoplasm.
What does the sarcoplasmic reticulum in relation to muscle contraction?
The sarcoplasmic reticulum stores and release calcium ions that are needed for muscle contraction.
Why do muscle fibres have a lot of mitochondria?
Muscle fibres have a lot of mitochondria to provide the ATP that’s needed for muscle contraction.
muscles cells contain many cells, this is called?
They are multinucleate.
Muscle fibres have lots of long, cylindrical organelles called …
myofibrils.
What makes up myofibrils?
They’re made up of proteins and are highly specialised for contraction.
Myofibrils contain bundles of:
thick and thin myofilaments that move past each other to make the muscle contract.
Thick myofilaments are made of the protein …
myosin
Thin myofilaments are made of the protein …
actin.
If you look at a myofibril under a microscope you’ll see a pattern of:
alternating dark and white bands.
Dark bands contain the …
thick myosin filaments and some overlapping thin actin filaments - these are called A-bands.
Light bands contain…
thin actin filaments only these are called L bands.
A myofibril is made up :
short units called sarcomeres.
The ends of each sarcomere are marked with a…
Z line.
In the middle of each sarcomere is an …
M line.
What is the m line?
The M-line is the middle of the myosin filaments.
Around the M-line is the …
H-Zone.
The H-zone only contains…
myosin filaments.
Myosin and actin filaments slide over another to make :
the sarcomeres contract, the myofilaments themselves don’t 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.
What structure do myosin filaments have that are hinged?
Myosin filaments have globular heads that are hinged, so they can move back and forth.
Does myosin have a binding site? Explain.
Each myosin head has a binding site for actin and a binding site for ATP.
Do Actin filaments have binding sites?
Actin filaments have binding sites for myosin heads, called actin myosin-binding sites
What two other proteins are found between actin filaments?
Two other proteins called tropomyosin and troponin are found between actin filaments.
What is the purpose of troponin and tropomyosin being attached together?
These proteins are attached to each other and they help myofilaments move past each other.
In a resting (unstimulated) muscle the actin myosin-binding site is blocked by …
tropomyosin, which is held by troponin.
What is the reason for tropomyosin blocking the actin-myosin binding site?
So myofilaments can’t slide past each other because the myosin heads can’t bind to the actin myosin-binding site on the actin filaments.
What happens when the action potential from a motor neurone stimulates a muscle cell?
When an action potential from a motor neurone stimulates a muscle cell, it depolarises the sarcolemma
What happens to depolarisation after the sarcolemma?
Depolarisation spreads down the T-tubules to the sarcolemma reticulum.
What does the action potential cause the sarcoplasmic reticulum to release?
Calcium ions into the sarcoplasm.
Calcium ions bind to troponin, causing it to …
change shape.
What happens after when the troponin binds to the calcium ions.
Calcium ions bind to troponin, causing it to change shape. This pulls the attached tropomyosin out of the actin-myosin binding site on the actin filament.
What happens after, when tropomyosin is pulled out of the actin-myosin active site?
This exposes the binding site, which allows the myosin head to bind.
The bond formed when a myosin head binds to an actin filament is called an:
actin-myosin cross bridge.
Calcium ions also activate the enzyme…
ATPase
ATPase breaks down …
ATP (into ADP + P) to provide the energy needed for muscle contraction.
The energy released from ATP moves the…
myosin head which pulls the actin filament along in a kind of rowing action.
ATP also provides the energy to break the actin-myosin cross-bridge, so the…
myosin head detaches from the actin filament after it’s moved.
The myosin head reattaches to a …
the different binding site further along the actin filament. A new actin-myosin cross-bridge is formed and the cycle is repeated.
How do cross-bridges cause muscle contraction?
Many cross-bridges form and break very rapidly, pulling the actin filaments along-which shortens the sarcomere, causing the muscle to contract.
What happens to the calcium ions when the muscles stop being stimulated?
When the muscles stop being stimulated, calcium ions leave their binding sites on the troponin molecules and are moved by active transport back into the sarcoplasmic reticulum.
What happens to the troponin molecule when the calcium ions leave the active site?
The troponin molecules return to their original shape, pulling the attached tropomyosin molecules with them. This means tropomyosin molecules block the actin-myosin binding site again.
Muscles aren’t contracted because…
no myosin heads are attached to actin filaments.
What happens to the actin filaments when the muscle does not contract?
The actin filaments slide back to their relaxed position, which lengthens the sarcomere.
(Aerobic respiration) Most ATP is generated via…
Oxidative phosphorylation in the cell’s mitochondria
(Aerobic respiration) aerobic respiration only works when there’s oxygen so it’s good for…
long periods of low-intensity exercise.
(Anaerobic respiration) ATP is made rapidly with …
glycolysis
(Anaerobic respiration) The end product of glycolysis is…
pyruvate, which is converted into lactate by lactate fermentation.
(Anaerobic respiration) Lactate can quickly build up in the muscles and cause…
muscle fatigue.
(Anaerobic respiration) Anaerobic respiration is good for…
short periods of hard exercise.
(ATP-Creatine Phosphate (CP) System) ATP is made by …
Phosphorylating ADP adding a phosphate group taken from creatine phosphate.
(ATP-Creatine Phosphate (CP) System) CP is STORED … and the ATP-CP system generates ATP very quickly.
inside cells
CP runs out after a few seconds so it’s used during …
short bursts of vigorous exercise.
The ATP-CP system is anaerobic and it’s …
alactic (it doesn’t form any lactate)
What is a neuromuscular junction?
A neuromuscular junction is a synapse between a motor neurone and a muscle cell.
Neuromuscular junctions use the neurotransmitter acetylcholine (ACh), which binds to receptors called…
nicotinic cholinergic receptors.
Neuromuscular junctions work in the same way as …
synapses between neurones they release a neurotransmitter, which triggers depolarization in the postsynaptic cell.
Depolarisation of a muscle cell always…
causes it to contract (if the threshold level is reached)
Acetylcholinesterase (AChE) stored in clefts on…
the postsynaptic membrane is released to break down acetylcholine after use.
Sometimes a chemical (e.g. a drug) may block the release of the neurotransmitter or affect the way it…
binds on the receptor on the postsynaptic membrane.
When a chemical binds to the receptor, it may prevent the action potential from being passed on to…
the muscle, so the muscle won’t contract.
Inhibiting muscle contraction could prove fatal if it affects the muscles involved in…
breathing, e.g. the diaphragm and intercostal muscles. If they can’t contract, ventilation can’t take place and the organism can’t respire aerobically.
Skeletal muscle contraction is controlled…
consciously.
Skeletal muscle is made up of many fibres that have…
many nuclei.
You can see regular … (a striped pattern) under the microscope.
cross-striations
Some muscle fibres contract very quickly - they’re used for…
speed and strength but fatigue quickly.
Some muscle fibres contract slowly and fatigue slowly - they’re used for…
endurance and posture.
What would you see under a microscope of a skeletal muscle?
> Cross striation - alternating dark and light pink stripes these are the A bands and L bands
> Many nuclei in each muscle fibre.
Involuntary muscle contraction is controlled…
unconsciously.
Involuntary muscle contraction is called smooth muscle because…
it doesn’t have the striped appearance of voluntary muscle.
smooth muscle is found in the walls of your…
hollow internal organs, e.g the gut, the blood vessels.
your gut smooth muscles contract to move food along, this is called…
peristalsis.
Your blood vessel smooth muscles contract to …
reduce the flow of blood.
Each muscle fibre has one…
nucleus.
The muscle fibres are …, and they’re only 0.2mm long.
spindled shaped with pointed ends.
The muscles contract…
slowly and don’t fatigue.
Cardiac muscles contract on its own - it’s…
myogenic
The rate of contraction in the cardiac muscles is controlled involuntarily by the…
autonomic nervous system.
Cardiac muscles are found in the …
walls of your heart.
Cardiac muscles are made of muscle fibres connected by…
intercalated discs, which have low electrical resistance so nerve impulses pass easily between cells
The muscle fibres are branched to allow…
nerve impulses to spread quickly through the whole muscle.
Each muscle fibre in the cardiac muscle only has…
one nucleus.
The muscle fibre in the cardiac muscles is shaped like…
cylinders and they’re about 0.1mm long.
You can see some cross-striations but the striped pattern isn’t as strong as it is in the…
voluntary muscle.
Cardiac muscles contract…
rhythmically and don’t fatigue.
If you have access to specialist equipment you may be able to investigate muscle contraction and fatigue by monitoring the … that occurs.
electrical activity.
Muscles contract in response to nerve impulses these are …
electrical signals.
Electrical signals in muscles can be detected by …. places on the skin
electrodes.
Electrodes connected to a computer produces electrical signals, this procedure is called…
electromyography.
Electromyography generates electrical signal readings which is called
electromyogram.
First of all, you need to attach … to places that you want to record from.
two electrodes.
A third electrode goes on an … (such as the bony wrist area to act as a control.)
inactive point
Switch off any other electrical equipment as this generates …
a noise that interferes with electrical signals from the muscle.
Connect the electrodes to an …
amplifier and a computer.
Keep the muscles… you should see a straight line on the electromyograph.
relaxed.
Then contract the muscle by bending your arm. You should see spikes on the graph as … are activated to contract muscles.
motor units.
If you then lift a weight, the amplitude of the trace on the graph will increase there are more…
electrical signals because more motor units are required to lift the weight.
If you continue to lift the weight your muscles will begin to …
fatigue.
During fatigue, the electromyograph amplitude will increase. This is because your brain is trying to activate …
more motor units to generate the force needed to hold the weight up.
