15. Nervous coordination and muscles Flashcards
(85 cards)
1
Q
How does the nervous system coordinate in animals?
A
Uses nerve cells to pass electrical impulses along their length. They stimulate their target cells by secreting chemicals, known as neurotransmitters, directly on to them. This results in rapid communication between specific parts of an organism. The responses produced are often short lived and restricted to a localised region of the body.
2
Q
Give an example of nervous transmission
A
Reflex action, such as the withdrawal of the hand from an unpleasant stimulus.
3
Q
What is a neurotransmitter?
A
One of a number of chemicals that are involved in communication between adjacent neurones or nerve cells and muscles.
4
Q
How does the hormonal system coordinate in animals?
A
Produces chemicals that are transported in the blood plasma to their target cells. The target cells have specific receptors on their cell surface membranes and the change in concentration of hormones stimulates them. This results in slower, less specific form of communication between parts of an organism. The responses are often long lasting and widespread.
5
Q
Give an example of hormonal coordination?
A
Control of blood glucose concentration, which produces a slower response with a long term and widespread effect.
6
Q
What is a ‘neurone’?
A
Neurones are specialised cells adapted to rapidly carrying electrochemical changes called nerve impulses from one part of the body to another.
7
Q
Describe a ‘cell body’ of a neurone
A
Contains all the usual cell organelles, including a nucleus and large amounts of RER, associated with production of proteins and neurotransmitters.
8
Q
Describe the ‘dendrons’ of the neurone
A
Extensions of the cell body which subdivide into smaller branched fibres, called dendrites, that carry nerve impulses towards the cell body.
9
Q
Describe the ‘axon’ of the neurone?
A
A single long fibre that carries nerve impulses away from the cell body.
10
Q
Describe the ‘schwann cells’ of a neurone
A
Surround the axon, protecting it and providing electrical insulation. They also carry out phagocytosis and play a part in nerve regeneration. Schwann cells wrap themselves around the axon many times, so that layers of their membranes build up around it.
11
Q
Describe the differences between the hormonal and nervous system of coordination
A
Hormonal- communicate by hormones. Nervous- communicate by nerve impulses.
Hormonal- transmit in blood. Nervous- transmit by neurones.
Hormonal- transmission is slow. Nervous- transmission is rapid.
Hormonal- travels to all parts of the body, but only target cell respond. Nervous- travel to specific parts of the body.
Hormonal- response is widespread.
Nervous- Response is localised.
12
Q
Describe the ‘myelin sheath’ of a neurone
A
Forms a covering to the axon and is made up of the membranes of the Schwann cells. These membranes are rich in a lipid known as myelin.
13
Q
Describe the ‘node of Ranvier’ of neurones
A
Constructions between adjacent Schwann cells where there is no myelin sheath. The constructions are 2-3 um long.
14
Q
What is a sensory neurone?
A
Transmits nerve impulses from a receptor to an intermediate or motor neurone. a they have one dendron that is often very long. It carries the impulse towards the cell body and one axon that carries it away from the cell body.
15
Q
What are motor neurones?
A
Transmits nerve impulses from a relay neurone to an effector, such ad a gland or muscle. Motor neurones have a long axon and many short dendrites.
16
Q
What is a relay neurone?
A
Transmits impulses between neurones, they have numerous short processes.
17
Q
How is the movement of ions, such as sodium and potassium, across the axon membrane controlled?
A
- The phospholipid bolster of the axon plasma membrane prevents sodium and potassium ions from passing through it.
- Channel proteins span the phospholipid bilayer. These proteins have ion channels, with ‘gates’ which can be opened or closed so that sodium/potassium ions can move through by facilitated diffusion. Some. channels remain opened all the time.
- Sodium potassium pump: Carrier proteins actively transport potassium ions into and sodium ions out of the axon
18
Q
Define nerve impulse
A
A self-propagating wave of electrical activity that travels along the axon membrane. It is a temporary reversal of the electrical potential difference across the axon membrane.
The reversal is between 2 states, the resting potential and action potential.
19
Q
What is the resting potential?
A
The difference in electrical charge maintained across the membrane of the axon of the neurone when not stimulated.
The inside of an axon is negatively charged, relative to the outside, due to membrane controls. The resting potential ranges from -50-90 mV. In this condition the axon is said to be polarised.
20
Q
Describe how the resting potential is established
A
-The sodium potassium pump actively transports sodium ions out of the axon and potassium ions into the axon.
-3 sodium ions move move out for every 2 potassium ions that move in.
-Despite Na+ & K+ both being positively charged, the outward movement of sodium ions is greater than the inward movement of potassium ions, creating an electrochemical gradient.
-The sodium ions begin to diffuse back naturally into the axon while the potassium ions begin to diffuse back out of the axon.
-However, most of the gates in the channels that allow the potassium ions to move through are open, while most of the gates in the channels that allow the sodium ions to move through are closed.
The axon is polarised. Inside = negatively charged.
21
Q
Describe how the action potential is generated
A
- Stimulus if a sufficient size is detected by a receptor in the nervous system, causing a temporary reversal of charge either side of the axon membrane.
- The channels in the axon change shape, and open to allow sodium ions to diffuse into the neurone down the sodium ion electrochemical gradient.
- If the potential difference meets the threshold value of -55mV, more sodium ion channels open.
- Depolarisation- The negative charge of -65mV becomes a positive charge of +40mV.
- Repolarisation- At a PD of +40mV, the sodium ion channels close and potassium ion channels open. The membrane is more permeable to potassium so potassium ions diffuse out of the neurone down the cone gratin gradient. This starts to get the membrane back to its resting potential.
22
Q
What is ‘hyperpolarisation’?
A
Potassium ion channels are too slow to close so there’s a slight ‘overshoot’ where too many potassium ions diffuse out of the neurone. The potential difference becomes more negative than the testing potential (less than -70mV)
23
Q
Why does the action potential move along the neurone as a wave of depolarisation?
A
- When an action potential happens, some of the sodium ions diffuse sideways.
- This causes sodium ion channels in the next region of the neurone to change and sodium ions diffuse into that part.
- This causes a wave of depolarisation to travel along the membrane.
- The wave moves away from the parts of the membrane in the refractory period because these parts can’t fire an action potential.
24
Q
How does an action potential pass along a myelinated axon?
A
The fatty sheath of myelin around the axon acts as an electrical insulator, preventing action potentials. There are breaks in the myelin insulation, called nodes of Ranvier, and action potentials occur at these points. Localised circuses arise between adjacent nodes of Ranvier and action potentials jump from rode to rode in a process known as saltatory conduction.
25
Does action potential travel faster down the axon of a myelinayed neurone or an unmyelinayed neurone?
Myelinated neurone: in an unmyelinayed neurone the events of depolarisation have to take place all the way along an axon and this taxes more time.
26
Give the factors which affect the speed which an action potential travels
- Myelin sheath
- Diameter of the axon
- Temperature
27
How does the myelin sheath affect the speed in which an action potential travels?
The myelin sheath acts as an electrical insulator, preventing the action potential forming in the part of the axon covered in myelin. It does however jump from 1 node of Ranvier to another, saltatory condition. This increases the speed of conductance.
28
How does the axon diameter affect the speed in which an action potential travels?
The greater the diameter of axon, the faster the speed of conductance. This is due to less leakage of ions from a large axon.
29
How does the temperature affect the speed in which an action potential travels?
- The higher the temperature, the faster rate of ion diffusion, the faster the nerve impulse.
- The energy for active transport comes from respiration. Respiration is controlled by enzymes. Enzymes function rapidly at higher temperatures, until denaturation (where nerve impulses fail to conduct).
- Temperature is an important factor in response times in cold blooded animals whose body temperature varies in accordance with the environment.
- Temperature also affects the speed & strength of muscle contractions.
30
What is the threshold value?
A certain level of stimulus which triggers an action potential, and therefore a nerve impulse.
31
How can an organism perceive the size of a stimulus?
- By the number of impulses passing in a given time. The more impulses generated, the larger the stimulus.
- By having different neurones with different threshold values. The brain interprets the number and type of neurones that pass impulses as a result of a given stimulus and thereby determines its size.
32
What is the refractory period?
once an action potential has been generated in any region of the axon, that is a period afterwards when an inward movement of sodium ions is prevented because the sodium voltage gated channels are closed. During this time it is impossible for a further action potential to be generated.
33
What’s the purpose of the refractory period?
- it insures that action potentials are propagated in one direction only: Action potentials can only pass from an active region to a resting region. This is because action potentials cannot be propagated in a region that is refractory, they can only move in a forward direction. This prevents action potentials from spreading out in both directions.
- it produces discrete impulses: due to the refractory period, a new action potential cannot be formed immediately behind the first one.
- It limits the number of action potentials: As action potentials are separated from one another this limits the number of action potentials that can pass along an axon in a given time, and limits the strength of the stimulus that can be detected.
34
Explain how the refractory period insures that the nerve impulses are kept separate from one another.
During the refractory period the sodium voltage gated channels are closed so no sodium ions can move inwards and no action potential is possible.
This means that there must be an interval between the one impulse and next.
35
State the all or nothing principle
There is a particular level of stimulus that triggers an action potential.
At any level above this threshold, a stimulus will trigger an action potential that is the same regardless of the size of the stimulus. Below the threshold, no action potential is triggered.
36
Earthworms have unmyelinated axons and so to increase the speed of conduction of action potentials these are relatively large in diameter.
Suggest two reasons why mammals do not require large diameter axons to achieve rapid transmission of action potentials.
Mammals have myelinated neurons and so have saltatory conduction. Mammals are endothermic and their constant, high body temperature increases the rate of diffusion of ions across the axon membrane and hence the speed of conduction of the action potential.
37
Describe the structure of a synapse
Synapses transmit information, not impulses, from one neuron to another by means of neurotransmitters. Neurons are separated by a small gap called the synaptic cleft. The neuron releases the transmitter is called the presynaptic neuron. The axon of this neuron and is in a swollen potion known as the synaptic knob. This possesses many mitochondria and large amounts of endoplasmic reticulum. These are required in the manufacture of the neurotransmitter which takes place in the axon.The neurotransmitter is stored in synaptic vesicles.Once the neurotransmitter is released from the vesicles, it transports to the postsynaptic neuron, which possesses specific receptor proteins on its membrane to receive it.
38
Give the main features of synapses
- Unidirectionality
- Summation (rapid build up of neurotransmitter in the synapse)
- Inhibition
39
What is spatial summation?
A number of different presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the postsynaptic neurone. Together they trigger a new action potential.
40
What is temporal summation?
A single presynaptic neuron releases neurotransmitter many times over a short period.
If the concentration of the neurotransmitter exceeds the threshold value of the post synaptic neuron then a new action potential is triggered.
41
Describe how inhibitory synapses prevent an action potential
-The presynaptic neurone releases the type of neurotransmitter that binds to chloride ion protein channels in the post synaptic neurone.
-The neurotransmitter causes the chloride ion protein channels to open.
-Chloride ions move into the postsynaptic neuron by facilitated diffusion.
-The binding of the neurotransmitter cause the opening of nearby potassium protein channels.
potassium ions move out of the postsynaptic neuron into the synapse.
-This combined effect of negatively charged chloride ions moving in, and positively charged potassium ions moving out, makes the inside of the postsynaptic membrane more negative and the outside more positive.
-this membrane potential increases to as much as -80mV.
This is called hyperpolarisation and makes it less likely that a new action potential will be created because a larger influx of sodium ions is needed to produce one.
42
State the functions of synapses
Act as junctions allowing…
- A single impulse along one neuron to initiate new impulses in a number of different neurons at a synapse. This allows a single stimulus to create a number of simultaneous responses.
- A number of impulses to be combined at a synapse.This allows nerve impulses from receptors reacting to different stimuli to contribute to a single response.
43
what neurotransmitter is released at cholinergic synapse?
Acetylcholine
44
Describe the mechanism of transmission across a cholinergic synapse
1. The arrival of an action potential at the end of the presynaptic neurone causes calcium ion protein channels to open and Ca2+ enter the synaptic knob by facilitated diffusion
2. This causes synaptic vesicles to fuse with the pre-synaptic membrane, releasing acetylcholine into the synaptic cleft.
3. Acetylcholine diffuses along the narrow synaptic cleft quickly because the diffusion pathway is short. Acetylcholine binds to receptors on sodium ion protein channels in the membrane of the postsynaptic neurone. This causes sodium ion protein channels to open, allowing sodium ions to diffuse in along a concentration gradient.
4. This generates a new action potential in the post synaptic neurone.
5. Acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid, which diffuse back across the synaptic cleft into presynaptic neurone. The rapid breakdown of acetylcholine also prevents it from continuously generating a new action potential in the post synaptic neurone, and so leads to discrete transfer of information across synapses.
6. ATP is released by mitochondria is used to re-combine choline and ethanoic acid into acetylcholine. This is stored in synaptic vesicles for future use. Sodium ion protein channels close in the absence of acetylcholine in the receptor sites.
45
Explain how presynaptic neuron is adapted for the manufacture of neurotransmitter
It possesses many mitochondria and large amounts of endoplasmic reticulum
46
Explain how the postsynaptic neuron is adapted to receive the neurotransmitter
It has receptor molecules for the neurotransmitters on its membrane.
47
If a neurone is stimulated in the middle of its axon, an action potential will pass both ways along it to the synapses at the end of the neuron. However the action potential will only pass across the synapse at one end. Explain why
Only one end can produce neurotransmitter and so this end alone can create a new action potential and the neurone on the opposite side of the synapse. At the other end there is no neurotransmitter that can be released to pass along the synapse and so no new action potential can be set up.
48
When walking along the street we barely notice the background noise of traffic. However we often respond to loud noises such as the sound of a horn.From your knowledge of summation explain the difference.
The relatively quiet background noise of traffic produces a low-level frequency of action potentials in the sensory neurons from the ear. The amount of neurotransmitter released into the synapse is insufficient to exceed the threshold in the postsynaptic neurone and so the noise is filtered out. Loud noises create a higher frequency and the amount of neurotransmitter released is sufficient to trigger an action potential in the postsynaptic neuron so there is a response. this is an example of temporal summation. In which a single presynaptic neurone releases neurotransmitter many times over a very short period.
49
Suggest an advantage in responding to high-level stimuli but not to low-level ones
Reacting to low-level stimuli that present little danger can overload the central nervous system and so organisms may fail to respond to more important stimuli.High-level stimuli need a response because they are more likely to represent danger.
50
Give examples of how drugs affect the action of neurotransmitters at synapses
- Some drugs, called agonists, have the same shape as neurotransmitters so they mimic that action at receptors. This means more receptors are activated, for example nicotine mimics acetylcholine and binds to nicotine cholinergic receptors in the brain.
- Some drugs, called antagonists, block receptors so they can’t be activated by neurotransmitters. This means fewer receptors can be activated.
- Some drugs inhibit the enzyme that breaks down neurotransmitters.This means there are more neurotransmitters in the synaptic cleft to bind to receptors and they’re there for longer.
- Some drugs simulate The release of neurotransmitter from the pre-synaptic neuron so more receptors are activated
- Some drugs inhibit the release of neurotransmitters from the presynaptic neuron so fewer receptors are activated, eg alcohol
51
Where is cardiac muscle found?
The heart.
| Under unconscious control.
52
Where is smooth-muscle found?
The walls of blood vessels and the gut.
| Unconscious control.
53
Where is skeletal muscle found?
Makes up the bulk of body muscle invertebrates. It is attached to bone and acts under voluntary conscious control.
54
How are muscles adapted for contraction?
- Grouped into myofibrils which have strong collective force.
- The separate cells are fused together into muscle fibres.These muscle fibres share nuclei and cytoplasm, called sarcoplasm, which is mostly found around the circumference of the fibre and contains a large concentration of mitochondria and endoplasmic reticulum.
55
What are the two types of protein filament that make up myofibrils?
- Actin: thin and consist of 2 strands twisted around each other.
- Myosin: thick and consists of long rod shaped tails with bulbous heads.
56
When looking at myofibril under an electron microscope why can you observe a pattern of dark and light bands?
- Dark bands contain thick myosin filaments and some overlapping actin filaments: A bands
- Light bands contain thin actin filaments only: I bands.
57
What is the Z line?
The end of each sarcomere
58
What is the M line?
The middle of each sarcomere, and the middle of myosin filaments.
59
What is the H zone?
Around the M line, only contains myosin filaments.
60
What is skeletal muscle used for in the body?
Movement.
| Muscles act as effectors and are stimulated to contact by neurones.
61
Why are muscles referred to as ‘antagonistic pairs’?
- The contracting muscle is the agonist
| - The relaxing muscle is the antagonist
62
What is tropomyosin?
An important protein found in muscle, form long thin strands that wrap around the actin filament.
63
What are the 2 types of muscle fibre?
- Slow twitch fibres
| - Fast twitch firbes
64
Compare slow twitch and fast twitch fibres
Slow- Contract slowly, Fast - Contract quickly.
Slow- Muscles used for posture, Fast- Muscles used for fast movement.
Slow- Endurance activities, Fast- Speed and power activities
Slow- Work for long time without getting tired, Fast- Get tired easily.
Slow- Energy released through aerobic respiration. Lots of mitochondria and blood vessels supply oxygen, Fast- Energy released quickly through anaerobic respiration using glycogen. There are few mitochondria or blood vessels.
Slow- Red colour, rich in myoglobin, storing oxygen. Fast- white, don’t have much myoglobin, can’t store oxygen.
65
What is a neuromuscular junction?
The point where a motor neurone meets skeletal muscle fibre. Many junctions along a muscle, for rapid and coordinated contraction when stimulated by action potentials.
66
What is a motor unit?
All muscle fibres supplied by a single motor neurone act together as a single functional unit. If only a slight force needed only a few units stimulated. If greater force required, larger units stimulated.
67
Explain how the neuromuscular junction receives a nerve impulse.
When a nerve impulse is received at the neuromuscular junction, the synaptic vesicles fuse with the pre-synaptic membrane and release their acetylcholine. The acetylcholine diffuses to the postsynaptic membrane, altering its permeability to sodium ions, Which enter rapidly depolarising the membrane. The acetylcholine is broken down by acetylcholinesterase to ensure the muscle is not over stimulated. The acetyl and ethanoic acid diffuse back into the neurone, where they’re recombined too corn acetylcholine using energy from mitochondria.
68
Compare a neuromuscular junction to a cholinergic synapse
Junction- Only excitatory. Synapse- May be excitatory or inhibitory.
Junction- Only links neurones to muscles. Synapse- Links neurones to neurones or other effector organs.
Junction- Only motor neurones involved. Synapse- motor, sensory and intermediate neurones.
Junction- action potential ends here. Synapse- another action potential may be produced along a post synaptic neurone.
Junction- acetylcholine binds to receptors oh membrane of muscle fibre. Synapse- acetylcholine binds to receptors on membrane of post synaptic neurone.
69
Suggest a reason why there are numerous mitochondria in the sarcoplasm
Muscles require much energy for contraction. Most of this energy is released during the krebs cycle and electron transport chain in respiration. Both these take place in mitochondria.
70
If we cut across a myofibril at certain points, we see only thick myosin filaments. Cut at different points and we see only thin actin filaments. At other other points we see both types of filament. Explain why.
The actin and myosin filaments lie side by side in myofibril and overlap at the edges where they meet. If cut where they do not overlap we see one or other filament only. If cut where they do overlap both filaments can be seen.
71
Explain how slow twitch fibres are adapted to contract slowly.
Slow twitch fibres have myoglobin to store oxygen, much glycogen to provide a source of metabolic energy, a rich supply of blood vessels to deliver glucose and oxygen, and lots of mitochondria to produce ATP
72
How are fast-twitch fibres adapted for quick muscle contraction?
Fast twitch fibres have thicker and more numerous myosin filaments, a high concentration of enzymes involved in anaerobic respiration and a store of phosphocreatine to rapidly generate ATP from ADP and anaerobic conditions.
73
Why do skeletal muscles have to occur and act in antagonistic pairs?
The contraction of skeletal muscle will move a part of the skelton in one direction, but the same muscle can’t move it in the opposite direction. Muscles can’t push, they only pull. To move the limb in the opposite direction requires a second muscle working antagonistically to the first one. In doing so it stretches it’s partner muscle, returning it to its original state ready to contact again. They pull in opposite directions, when one is contracted the other is relaxed.
74
Give evidence for the sliding filament mechanism
When the muscle contracts the following changes occur to a sarcomere:
-I band narrows
-Z lines move close together, sarcomere shortens
-H zone becomes narrower
The A band remains the same width, as the width of this band is determined by length of myosin filaments, it follows that the myosin has not become shorter. This discounts the theory that muscle contraction is due to the filaments themselves shortening.
75
What are the 3 main proteins involved in the sliding filament mechanism?
-Myosin, made up of 2 types of protein:
A fibrous protein tail, arranged into a filament of several hindered molecules.
A globular protein head, forming 2 bulbous structures at one end.
- Actin is a globular protein whose molecules are arranged into long chains that are twisted around one another to form a helical stand.
- Tropomyosin forms long thin threads that are wound around actin filaments.
76
Describe the sliding filament process of muscle contraction, part 1: muscle stimulation
- An action potential reaches many neuromuscular junctions simultaneously, causing calcium ion protein channels to open and calcium ions to diffuse into the synaptic knob.
- The calcium ions cause the synaptic vesicles to fuse with the presynaptic membrane and release acetylcholine into the synaptic cleft.
- Acetylcholine diffuses across the synaptic cleft and binds with receptors on the muscle cell surface membrane, causing it to depolarise.
77
Describe the sliding filament process of muscle contraction, part 2: muscle contraction
- An action potential travels deep into the river through a system of T tubules that are extensions of the cell membrane and branch throughout the sarcoplasm.
- The tubules are in contact with endoplasmic reticulum of the muscle, which has actively transported calcium ions from the sarcoplasm leading to very low Ca2+ concentration in sarcoplasm (muscle cytoplasm).
- The action potential opens the calcium ion protein channels on the endoplasmic reticulum, and calcium ions diffuse into the sarcoplasm down conc gradient.
- The calcium ions cause the tropomyosin molecules that were blocking the binding site on the actin filament to pull away.
- ADP molecule attached to the myosin heads mean they’re in a state to bind to the actin filament and form a cross bridge.
- Once attached to the actin filament, the myosin heads change their angle, pulling the actin filament along, releasing a molecule of ADP.
- An ATP molecule attaches to each myosin head, causing it to become detached from the actin filament.
- The calcium ions then activate the enzyme ATPase, which hydrolyses ATP to ADP, providing the energy for the myosin head to return to its original position.
- The myosin head, once more with an ADP molecule attached, reattached itself further along the actin filament and the cycle is repeated as long as the concentration of calcium ions in the myofibril remains high.
- As the myosin are joined tail to tail in 2 oppositely facing sets, the movement of one set of myosin heads is in the opposite direction to the other set. This means the actin filaments to which they’re attached also move in opposite directions.
- The movement of actin filaments in opposite directions pulls them towards each other, shortening the distance of the 2 adjacent Z lines. The effect of this process taking place repeatedly and simultaneously throughout a muscle is to shorten it and bring about movement in the body.
78
Describe the sliding filament process of muscle contraction, part 3: muscle relaxation
- When a nervous stimulation eases calcium ions are actively transported back into the endoplasmic reticulum using energy from the hydrolysis of ATP.
- This re absorption of calcium ions allows tropomyosin to block the actin filament again. Myosin heads are now unable to bind to actin filaments, contraction ceases, muscle relaxes.
79
Muscle contraction requires considerable energy, how is this supplied?
From the hydrolysis of ATP to ADP and an inorganic phosphate.
80
What is the energy used for in muscle contraction?
- The movement of the myosin heads
| - The reabsorption of calcium ions into the endoplasmic reticulum by active transport
81
Generating ATP aerobically requires oxygen. In a very active muscle the demand for ATP, and therefore oxygen, is greater than the rate that the organism can supply oxygen. How can ATP be generated in this circumstance?
Anaerobic respiration. This is achieved by using a chemical, phosphocreatine and more glycolysis.
Phosphocreatine cannot supply energy directly to the muscle so instead regenerates ATP. Phosphocreatine is stored in muscle and acts as a reserve supply fo phosphate why is available immediately to combine with ADP and reform ATP. The phosphocreatine store is replenished using phosphate from ATP when muscle is relaxed.
82
Explain how the shape of myosin is adapted to muscle contraction
Myosin is made of 2 proteins. The fibrous protein is long and thin in shape, enabling it to combine with others to form a long thick filament along with which the actin filament can move. The globular protein forms 2 bulbous heads at the end of a filament. This shape allows it to exactly fit recesses in the actin molecules to which it can become attached. It’s shape also means it can be moved at an angle. This allows it to change it’s angle when attached to the actin, moving it along, causing contraction of muscle.
83
Trained sprinters have high levels of phosphocreatine in the muscles. Explain the advantage of this.
Phosphocreatine stores the phosphate that is used to generate ATP from ADP in anaerobic conditions. A sprinters muscles often work so strenuously so that oxygen supply cannot meet the demand. The supply of ATP from mitochondrial during aerobic respiration therefore ceases. Sprinters with the most phosphocreatine have an advantage because ATP can be supplied to their muscles for longer and they can perform better.
84
During the contraction of a muscle sarcomere, a single actin silent moves 0.8 um. If hydrolysis of a single ATP provides enough energy to move an actin filament 40 nm, calculate how many ATP molecules are needed to move the actin filament 0.8um.
1 ATP= moves actin 40nm
Total distance be moved by actin = 0.8um= 800nm
Number of ATP required to move 800nm = 800/40 = 20 ATPs
85
Dead cells can no longer produce ATP. Soon after death, muscles contract, making the body stiff- ‘rigor mortis’ From your knowledge of muscle contraction, explain why rigor mortis occurs after death.
One role of ATP in muscle contraction is to attach to the myosin heads, thereby causing them to detach from the actin filament and making the muscle relax. As no ATP is produced after death, there’s none to attach to the myosin which therefore remains attached to the actin, leaving the muscle in a contracted state.
