Nervous Coordination And Muscles: Chapter 15 Flashcards
1
Q
What are the 2 main forms of coordination in animals as a whole?
A
The nervous system and the hormonal system
2
Q
Briefly describe the nervous system
A
Uses nerve cells to pass electrical impulses along their length. They stimulate their target cells by secreting neurotransmitters directly onto them
3
Q
What is an example of nervous coordination?
A
Reflex action
4
Q
Briefly describe the hormonal system
A
Produces hormones that are transported in 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
5
Q
What is an example of hormonal communication?
A
Control of blood glucose concentration
6
Q
What are they key differences between the nervous system and the hormonal system?
A
Nervous system:
- communication is by nerve impulses
- transmission is by neurones
- transmission is very rapid
- nerve impulses travel to specific parts of the body
- response is localised
- response is rapid
- response is short-lived
- effect is usually temporary and reversible
Hormonal system:
- communication by hormones(chemicals)
- transmission is by the blood system
- transmission is usually relatively slow
- hormones travel to all parts of the body, but only target cells respond
- response is widespread
- response is slow
- response is often long-lasting
- effect may be permanent and irreversible
7
Q
Neurones (nerve cells) are specialised cells adapted to
A
Rapidly carry electrochemical changes called nerve impulses from one part of the body to another
8
Q
A motor neurone is made up of:
A
- a cell body: contains all usual cell organelles including a nucleus and large amounts of rough ER- this is associated with production of proteins and neurotransmitters
- dendrons: extensions of the cell body which subdivide into smaller branched fibres called dendrites that carry nerve impulses away from the cell body
- Schwann cells: surround the axon, protecting it and providing electrical insulation
- myelin sheath: which forms a covering to the axon and is made up of membranes of Schwann cells- these membranes are rich in lipid known as myelin
- nodes of ranvier: constrictions between adjacent Schwann cells where there is no myelin sheath
9
Q
Reflexes are very fast,describe how the structure of a reflex ensures a fast response
A
Minimum number of synapses and neurones make reflexes very fast
10
Q
What’s the correct way to write potassium ion?
A
K+
11
Q
What’s the correct way to write sodium ion?
A
Na+
12
Q
What are the 3 stages in creating an impulse (action potential)?
A
1- resting potential needs to be set up (polarised membrane) ( approx -70V)
2- depolarisation (approx +30V)
3- repolarisation (back to -70V)
13
Q
Why does a resting potential need to be set up in the neurone?
A
Needs to be present in order to allow an impulse to be transmitted
14
Q
During resting potential, the neurone is not sending an impulse but
A
It is actively getting trade to do so
15
Q
Define resting potential
A
Is the potential across the plasma membrane of a cell that is not conducting an impulse
16
Q
Explain how a resting potential is maintained in a neurone
A
- 3 sodium ions are actively transported out of the axon
- 2 potassium ions are actively transported into the axon
- by the sodium-potassium pump
- potassium ion channels are open so potassium ions diffuse into the axon
- sodium ion gate is closed so sodium ions cannot diffuse into the axon
- membrane is said to be polarised as there is a positive charge on the outside of the axon with a less positive charge on the inside of the axon
17
Q
What occurs in stage 2 (depolarisation)?
A
Action potential is created across the membrane and action potential moves along the axon to create an impulse
18
Q
Describe how an action potential is created in a neurone
A
- sodium ion channel opens and sodium ions diffuse into the axon along the concentration gradient
- potassium ions cannot move as potassium ion channel closed
- inside of axon becomes more positively charged and outside becomes less positively charged (depolarisation)
19
Q
What occurs in stage 3 (repolarisation)?
A
Membrane becomes polarised again and resting potential is re-established. An action potential cannot be generated until the resting potential is produced
20
Q
Describe how repolarisation occurs
A
- potassium ion channels open soon after the sodium ion channel open when action potential was generated
- potassium ions diffuse out of the axon
- sodium ions trapped inside the axon as sodium ion channels close
- charge outside of axon becomes more positively charged
- sodium-potassium pump starts again and so sodium ions are actively transported out the axon
21
Q
What is saltatory conduction?
A
- action potential is set up at the node of Ranvier
- this impulse jumps to the next node of Ranvier
- this enables the impulse to travel more rapidly
22
Q
Saltatory conduction can only occur in
A
Myelinated neurones
23
Q
How is an impulse propagated down a neurone?
A
- resting potential is set up at each of the node of Ranvier. The sodium ion channels are closed
- an impulse arrives at the first node of Ranvier and sodium ions enter the axon
- the diffusion of sodium ions causes the sodium ion channels in the next node of Ranvier to open
- sodium ions enter the axon and cause the sodium ion channels in the next node to open
- action potential has moved to next node of Ranvier- impulse cannot travel backwards as resting potential not re-established
24
Q
What are the factors that affect the speed of impulses?
A
- myelination increases the speed of impulse transmission due to saltatory conduction
- axon diameter- the wider the axon, the greater the speed of conduction
- temperature- the higher the temperature, the greater the transmission speed due to faster diffusion of ions- however, in mammals and birds, body is kept constant so temperature should not have an effect
25
Nerve impulses are described as __-__-_____ responses
All-or-nothing
26
What is the all-or-nothing principle?
There is a certain level of stimulus called the threshold value, which triggers an action potential. Below the threshold value, no action potential and therefore no impulse is generated
27
Regarding the all-or-nothing principle, organisms perceive the size of the stimulus in 2 ways:
1- by the number of impulses passing in a given time- the larger the stimulus, the more impulses that are generated in a given time
2- by having different neurones with different threshold values
28
What is the purpose of the all-or-nothing principle?
The brain would be overloaded with information if it became aware of every little stimulus. The all-or-nothing nature of the action potential acts as a filter, preventing minor stimuli from setting up nerve impulses and thus preventing the brain becoming overloaded
29
What is the refractory period?
Once an action potential has been created in any region of the axon, there is a period afterwards when 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
30
Refractory period serves 3 purposes, what are they?
1- ensures action potentials are propagated in 1 direction: 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, which means that they can only move in a forward direction. This prevents action potentials from spreading out in both directions, which they would otherwise do
2- it produces discrete impulses: due to the refractory period, a new action potential cannot be formed immediately behind the first one. This ensures that action potentials are separated from one another
3- 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 thus limits the strength of the stimulus that can be detected
31
"Explain how the refractory period ensures that 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 there must be an interval between one impulse and the next
32
What is a synapse?
A junction between 2 neurones across which a neurotransmitter can pass
33
Synapses transmit information but not ______ from 1 neurone to another by the means of neurotransmitters
Impulses
34
Describe the structure of a synapse
- neurones are separated by a small gap called the synaptic cleft
- the neurone that releases the neurotransmitter is called the presynaptic neurone- the axon of this neurone ends in a swollen portion known as the synaptic knob that possesses many mitochondria and large amounts of ER required for the manufacture of neurotransmitters which takes place in the axon
- the neurotransmitter is stored in the synaptic vesicles
- once the neurotransmitter is released from the vesicles it diffuses across to the postsynaptic neurone which possesses specific receptor proteins on its membrane to receive it
35
Describe the steps of synaptic transmission:
1- action potential reaches end of the sensory neurone and sodium ions enters the axon
2- calcium channels in presynaptic membrane open allowing calcium ions to diffuse into presynaptic knob
3- calcium ions cause the vesicles containing acetylcholine to fuse with the presynaptic membrane
4- neurotransmitter is released into the synapse
5- acetylcholine diffuses across the synaptic cleft- acetylcholine binds to receptor proteins on post-synaptic membrane (complementary shape) and causes sodium channels to open on post synaptic membrane
7- sodium ions enter relay neurone
8- action potential generated at the next node of Ranvier
9- acetylcholinesterase breaks down acetylcholine into acetyl and choline which leaves the receptor protein
10- acetyl and choline diffuse across the synapse
11- acetyl and choline are reabsorbed into the presynaptic knob and condense to form acetylcholine
36
What are the features of synapses?
1- unidirectionality
| 2- summation
37
What is unidirectionality?
Synapses can only pass information in one direction from the presynaptic neurone to the postsynaptic neurone
38
Why are synapses unidirectional?
- calcium ion channels found only in the pre-synaptic membrane
- vesicles containing neurotransmitters only found in presynaptic membrane
- receptors for neurotransmitters only found in the post synaptic membrane
39
Explain summation
Low-frequency action potentials often lead to the release of insufficient concentrations of neurotransmitter to trigger a new action potential in the postsynaptic neurone. They can however, do so in summation: this enables a rapid build-up of neurotransmitter in the synapse by spatial summation or temporal summation
40
Explain spatial summation
A number of different presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the postsynaptic neurone. Together they therefore trigger a new action potential
41
Explain temporal summation
In which a single presynaptic neurone releases neurotransmitters many times over a very short period. If the concentration of neurotransmitter exceeds the threshold value of the postsynaptic neurone, then a new action potential is triggered
42
What do inhibitory synapses do?
Make it less likely that a new action potential will be created on the post synaptic neurone
43
How do inhibitory synapses work?
1- action potential reaches synaptic knob
2- calcium ion channels open and calcium ions enter
3- calcium ions cause vesicles to move to pre-synaptic membrane
4- neurotransmitter molecules bind to the receptor in the post-synaptic membrane
5- potassium and chloride channels open
6- potassium ions exit and chloride ions enter so the inside of the synaptic knob becomes more negative
7- postsynaptic membrane is less likely to reach threshold and an action potential is less likely (hyperpolarisation) as a larger influx of sodium ions is needed to produce one
44
Synapses transmit information from one neurone to another. In doing so, they act as junctions allowing:
- a single impulse along one neurone to initiate new impulses in a number of different neurones 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
45
"Explain how a presynaptic neurone is adapted for the manufacture of neurotransmitter"
Possesses many mitochondria and large amounts of ER
46
"If a neurone is stimulated in the middle of its axon, an action potential will pass both ways along it to the synapses at each of the neurone. 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 in the neurone on the opposite side of the synapse. At the other end there is no neurotransmitter that can be released to pass across the synapse and so no new action potential can be set up
47
"When walking along a street we barely notice the background noise of the traffic. However, we often respond to louder traffic noises such as the sound of a horn. With your knowledge of both temporal and spatial summation explain this difference"
- temporal summation= the relatively quiet background noise of traffic produces a low-level frequency of action potential in the sensory neurone from the ear. The amount of neurotransmitter released into the synapse is insufficient to exceed the threshold in the postsynaptic neurone and to trigger an action potential, so the noise is ignored. In contrast, much louder noises create a higher frequency and the amount of neurotransmitter released is sufficient to trigger an action potential in the postsynaptic neurone and so there is a response
- spatial summation= many sound receptors with a range of thresholds-> more receptors respond to the louder noise-> more neurotransmitter-> response
48
Suggest an advantage in responding to high-level stimuli but not low-level stimuli
Reacting to low-level stimuli that present little danger can overload the CNS and so organisms may fail to respond to high-level stimuli. High-level stimuli needs a response because they are more likely to represent a danger
49
What are the 3 types of muscle?
Smooth, cardiac and skeletal
50
Where is smooth muscle found?
In the walls of blood vessels and gut
51
Muscles are effector organs that respond to
Nervous stimulation by contracting and so bring about movement
52
Smooth and cardiac muscle is not under
Conscious control and we remain largely unaware of their contractions
53
Skeletal muscle makes up the bulk of the body muscle in vertebrates. It is attached to bone and acts
Under voluntary, conscious control
54
Individual muscles are made up of millions of tiny muscle fibres called
Myofibrils
55
In themselves, myofibrils produce almost no force while collectively they
can be extremely powerful
56
Myofibrils are lined parallel to each other in order to
give maximum force
57
Muscle is composed of smaller units bundled into
Progressively larger ones
58
Why would muscle not be able to perform the function of contraction effectively if muscle was made up of individual cells joined end to end
Because the junction between adjacent cells would be a point of weakness that would reduce the overall strength of the muscle; to overcome this muscles have a very different structure. The separate cells have become fused together into muscle fibres
59
Muscle fibres share
Nuclei and also cytoplasm called sarcoplasm
60
Within the sacroplasm is a large concentration of
Mitochondria and endoplasmic reticulum
61
Myofibrils are made up mainly of 2 types of protein filaments:
Actin and myosin
62
Compare actin and myosin
- actin is thinner and consists of 2 strands twisted around one another
- myosin is thicker and consists of long-rod shaped tails with bulbous heads that project to the side
63
Why do myofibrils appear striped?
Due to their alternating light-coloured and dark-coloured bands
64
Light bands=
I band (isotropic bands)
65
Why do I bands appear lighter?
Because the thick and thin filaments don't overlap in this region
66
Dark bands=
A bands (anisotropic bands)
67
Why do A bands appear darker?
The thick and thin filaments overlap in this region
68
The distance between adjacent Z lines is called a
Sarcomere
69
Another important protein found in muscle is
Tropomyosin
70
Tropomyosin forms a fibrous strand around the
Actin filaments
71
What are the 2 types of muscle fibre?
Slow-twitch fibre and fast-twitch fibre
72
The proportions of which type of muscle fibre vary from
Muscle to muscle
73
Describe slow-twitch fibres
- contract more slowly than fast-twitch
- provide less powerful contraction but but over a longer period
- adapted to endurance work e.g. running a marathon
- in humans more common in muscles like calf muscle which much contract constantly to keep body upright
74
Slow-twitch fibres are suited to their role by being adapted to aerobic respiration in order to avoid a build up of lactic acid, which would cause them to function less effectively and prevent long duration contraction. These adaptions include:
- a large store of myoglobin (a bright red molecule that stores oxygen, which accounts for the red colour of the slow-twitch fibres)
- rich supply of blood vessels to deliver oxygen and glucose for aerobic respiration.
- numerous mitochondria to produce ATP
75
Describe fast-twitch fibres
- contract rapidly
- powerful contraction but only for a short period = adapted to intense exercise e.g. weight lifting = more common in muscles which need to do short bursts of intense activity, like the bicep muscles of the upper arm
76
Fast-twitch fibres are adapted to their role by having:
- thicker and more numerous myosin filaments
- a high concentration of glycogen
- a high concentration of enzymes involved in anaerobic respiration which provides ATP rapidly
- a store of phosphocreatine, a molecule that can rapidly generate ATP from ADP in anaerobic conditions and so provide energy for muscle contraction
77
What are neuromuscular junctions?
Where a motor neurone meets a skeletal muscle fibre- there are many such junctions along the muscle
78
Why is it good there are many neuromuscular junctions along a muscle?
If there were only one junction of this type it would take time for a wave of contraction to travel across the muscle, in which case not all the fibres would contract simultaneously and the movement would be slow
79
As rapid and coordinated muscle contraction is frequently essential for survival, there are many NM junctions spread throughout the muscle so
Contraction of a muscle is rapid and powerful when it is stimulated by an action potential
80
All muscle fibres supplied by a single motor neurone act together as a single functional unit and are known as _ _____ ____. This arrangement gives control over the force that muscle exerts e.g. if only slight force is needed only a few units are stimulated. If a great force is needed a large number of units are stimulated
A motor unit
81
How is an action potential created across a neuromuscular junction?
- The synaptic vesicles fuse with the presynaptic membrane and release their acetylcholine
- the acetylcholine diffuses to the postsynaptic membrane (membrane of muscle fibre) altering its permeability to sodium ions which enter rapidly depolarising the membrane
- acetylcholine is broken down by acetylcholinesterase to ensure that the muscle is not overstimulated
- resulting acetyl and choline diffuse back into neurone where they are recombined to form acetylcholine using energy from mitochondria found there
82
What are some similarities between neuromuscular junctions and cholinergic synapses?
- have neurotransmitters transported by diffusion
- have receptors that on binding with neurotransmitter cause an influx of sodium ions
- use a sodium-potassium pump to depolarise axon
- use enzymes to break down neurotransmitters
83
What are some differences between neuromuscular junctions and cholinergic synapses?
- NMJ are only excitatory whereas synapses may be excitatory or inhibitory
- NMJ only involve motor neurones whereas with synapses motor, sensors and intermediate neurones may be involved
- with NMJ the action potential ends here ( end of a neural pathway) whereas with synapses another action potential may be produced along another neurone (postsynaptic neurone)
- with NMJ acetylcholine binds to receptors on membrane of muscle fibres whereas with synapses acetylcholine binds to receptors on membrane of post-synaptic neurone
84
Suggest a reason why there are numerous mitochondria in the sarcoplasm
Muscles require much energy for contraction. Most of the energy is released during the Krebs cycle and electron transport chain in respiration- both take place in the mitochondria
85
If we cut across a myofibril at certain limits we see only thick myosin filaments. Cut at different points, we see only thin actin filaments. At yet other points we see both of filaments. Explain why.
The actin and myosin filaments lie side by side in a myofibril and overlap at the edges where they meet. If cut where they overlap both filaments can be seen. If cut where they do not overlap we see one or other filaments only
86
Muscles act in _________ pairs
Antagonistic
87
Skeletal muscles are attached to bones by
Tendons
88
Ligaments attach bones to
Other bones, to hold them together
89
Pairs of skeletal muscles contact and relax to move bones at a
Joint
90
The bones of the Skelton are incompressible (rigid) so they act as
Levers (giving the muscle something to pull against)
91
Muscles that work together to move a bone are called antagonistic pairs. The contracting muscle is called the agonist and the relaxing muscle is called the
Antagonist
92
Give an example of antagonistic pairs
When your bicep contacts, your tricep relaxes- this pulls the bone so your arm bends (flexes) at the elbow. In this case, the bicep is the agonist and the tricep the antagonist
93
What does the sliding filament mechanism involve?
Process involves the actin and myosin filaments sliding past one another
94
Explain some evidence supporting sliding filament mechanism
Myofibrils appear darker in colour where the actin and myosin filaments overlap and lighter where they do not. If the SFM is correct, then there will be more overlap of actin in myosin in a contracting muscle than in a relaxed one.
When a muscle contracts the following occurs to a sarcomere:
- the I-band becomes narrower
- the Z-lines move closer together I.e. sarcomere shortens
- the H-zone becomes narrower
- the A-band remains same width- as width of this band is determined by the length of the myosin filaments it follows that the myosin filaments have not become shorter
- therefore discounts theory that muscle contraction is due to the filaments themselves shortening
95
What are the 3 main proteins involved in SFM?
- myosin = made up of 2 types of protein
)a fibrous protein arranged into a filament made up of several hundred molecules (the tail)
) a globular protein formed into 2 bulbous structures at one end (the head)
- actin= globular protein where molecules are arranged into long chains that are twisted around one another to form a helical strand
- tropomyosin = forms long thin threads that are wound around actin filaments
96
How does an action potential cause muscle contraction?
1- action potential arrives at the end of the motor neurone, at the neuromuscular junction
2- this causes the release of acetylcholine into the synapse
3- this initiates an action potential in the sarcolemma ( muscle cell membrane)
4- action potential is carried quickly into the large muscle cell by the T-tubules
5- action potential causes the sarcoplasmi reticulum to release its store of calcium ions into the myofibrils
6- calcium ions causes tropomyosin to be displaced uncovering myosin binding sites on actin
7- myosin cross-bridges can now attach and the cross bridge cycle can take place
8- myosin heads change their angle, pulling the actin filament along as they do so and releasing a molecule of ADP
9- ATP molecule attaches to each myosin head causing it to become detached from the actin filament
10- calcium ions activate the enzyme ATPase which hydrolysed the ATP to ADP, providing energy for the myosin head to return to original position
97
Explain muscle relaxation when nervous stimulation ceases
- when nervous stimulation ceases, calcium ions are actively transported back into the endoplasmic reticulum using energy from the hydrolysis of ATP
- this reabsorption of calcium ions allows tropomyosin to block the actin filaments again
- myosin heads are now unable to bind to actin filaments and contraction ceases, that is, the muscle relaxes
- in this state, force from antagonistic muscles can pull actin filaments out from between myosin (to a point)
98
How is myosin adapted to its role in muscle contraction?
- fibrous protein long and thin =provides surface area for which actin can move along
- globular proteins form bulbous structures = allows it to exactly fit the binding sites of actin filament
99
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. A sprinter's muscles often work so strenuously that the oxygen supply cannot meet the demand. The supply of ATP from mitochondria during aerobic respiration therefore ceases. Sprinters with the most phosphocreatine have an advantage because ATP can be supplied to their muscles for longer and so they perform better
100
- Huge quantities of ATP are needed for muscle contraction. Aerobic respiration cannot produce ATP fast enough. What molecule can be used to phosphorylate ADP?
- give the equation
- phosphocreatine
| - CP+ADP+Pi---> ATP+C
101
What is the role of ATP in myofibril contraction?
- allows binding of myosin to actin
- provides the energy for the myosin head to then pull the actin (power stroke).
- supplies the energy source for the myosin to detach from actin and to actively transport calcium ions back into the sarcoplasmic reticulum
- used to 'recock' the globular head on the myosin filament. This resets the muscle fibres and breaks the myosin cross bridges allowing further contraction to occur
- provides energy for myosin head to return to original position
102
Describe saltatory conduction
Propagation of a nerve impulse across a myelinated axon in which the action potential 'jumps' from one node of Ranvier to another
