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Grice/Hall AQA A-Level Biology Revision Year13 > 3.6.2.1 - 3.6.2.2 Nerve Impulses and Synapses > Flashcards

3.6.2.1 - 3.6.2.2 Nerve Impulses and Synapses Flashcards

1
Q

What is the difference in communication in terms of the hormonal and nervous system?

A

H: hormones
N: nerve impulses

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2
Q

What is the difference in transmission in terms of the hormonal and nervous system?

A

H: by the blood system, relatively slow
N: by neurones, very rapid

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3
Q

What is the difference in the response in terms of the hormonal and nervous system?

A

H: widespread, slow, long-lasting, effect may be permenant
N: localised, rapid, short-lived, usually temporary

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4
Q

What are the basic components of a motor neurone?

A 
Cell body
Dendrons
Axon
Schwann cells
Myelin sheath
Nodes of ranvier
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5
Q

What is a cell body?

A

It contains all the usual cell organelles including a nucleus and large amounts of rough ER

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6
Q

What are dendrons?

A

Extensions of the cell body which divide into smaller branches called dendrites
They carry nerve impulses towards the cell body

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7
Q

What is an axon?

A

A single long fibre that carries nerve impulses away from the nerve body

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8
Q

What are Schwann cells?

A

Cells which surround the axons, protecting it and providing electrical insulation
Wraps around the axon many times so the layers of the membranes build up

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9
Q

What is the purpose of the myelin sheath?

A

It forms a covering to the axon and is made up of the membranes of the Schwann cells
These membranes are rich in myelin

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10
Q

What are nodes of ranvier?

A

Constrictions between adjacent Schwann cells where there is no myelin sheath

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11
Q

What are the three types of neurones?

A

Motor, sensory or relay

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12
Q

What is the purpose of a sensory neurone?

A

Transmits nerve impulses from a receptor to a relay or motor neurone
Has one dendron
Dendron carries the impulse towards the cell body and one axon that carries it away from the cell body

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13
Q

What is the purpose of a motor neurone?

A

It transmits nerve impulses from a relay neurone to an effecor
Has a long axon and many short dendrites

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14
Q

What is the purpose of a relay neurone?

A

It transmits impulses between neurones, for example, from sensory to motor neurones
They have numerous short processes

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15
Q

What does the relay neurone look like?

A

See card

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16
Q

How do you draw a sensory neurone?

A

See card

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17
Q

How do you draw a motor neurone?

A

See card

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18
Q

What is a nerve impulse?

A

A self-propogating wave of electrical activity that travels along the axon membrane

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19
Q

What are the two ions which control the creation of an action potential?

A

Sodium (Na+)

Potassium (K+)

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20
Q

How is the movement of sodium and potassium ions controlled?

A

The phospholipid bilayer of the axon of the plasma membrane prevents the diffusion of ions
Gated channel proteins which allow facilitated diffusion
Sodium potassium pump (type of carrier protein)

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21
Q

What is the resting potential of the axon membrane?

A

65 mV

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22
Q

When can the axon be called polarised?

A

When the inside of an axon is negatively charged relative to the outside
This is the resting potential

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23
Q

How is the resting potential established?

A

Sodium ions are actively transported out of the axon by the sodium potassium pumps
Potassium ions are actively transported into the axon by the sodium potassium pumps
For every three sodium ions moving out, two potassium ions move in
More sodium moves out into the tissue fluid than potassium moves into which creates an electrochemical gradient
Sodium begins to diffuse back naturally into the axon while the potassium begins to diffuse back out of the axon
Most of the gates which allow the movement of potassium are open but most of the gates which allow the movement of sodium are closed

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24
Q

How is an action potential generated?

A

The energy of a stimulus causes some sodium voltage-gated channels to open
Sodium ions diffuse into the axon
This causes a reversal in the potential difference
As sodium diffuses into the axon, more sodium channels open which creates a greater influx by diffusion
Once an action potential of +40mV is reached, the voltage-gated sodium channels close and the voltage-gated potassium channels begin to open
The electrical gradient preventing the outward movement of potassium is now reversed, causing more potassium channels to open which causes potassium to move out
This starts the repolarisation of the axon
The outward diffusion of potassium ions causes a temporary overshoot with the inside being more negative than usual
The gates of the potassium channels close
The sodium-potassium pump pumps sodium out and potassium in to reach the normal resting potential of -65mV
It is now repolarised

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25
What is an action potential?
A travelling wave of depolarisation
26
How does an action potential move along the axon?
As one region becomes depolarised, it stimulates the depolarisation of the next region The previous region becomes depolarised The myelin sheath around the axon acts as an electrical insulator, preventing action potentials from forming Therefore the action potentials jump between nodes of ranvier This is quicker because depolarisation does not need to be created all along the axon
27
What is a nerve impulse?
The transmission of an action potential along the axon of a neurone
28
What are the three factors which affect the speed at which an action potential travels?
Myelin sheath Diameter of the axon Temperature
29
How does the myelin sheath affect the speed at which an action potential travels?
It acts as an electrical insulator which prevents an action potential forming in the part of the axon covered in myelin This causes the potential to jump between nodes of ranvier (saltatory conduction)
30
How does the diameter of the axon affect the speed at which an action potential travels?
The greater the diameter, the faster the speed of conductance This is due to less leakage of ions
31
How does the temperature of the axon affect the speed at which an action potential travels?
This affects the rate of diffusion of ions The higher the temperature, the faster the nerve impulse Respiration enzymes function more effectively at higher temperatures which provides more ATP for the sodium potassium pump This causes a faster movement of the action potential However if the temperature is too high, the enzymes will denature
32
Why can nerve impulses be described as following the all or nothing principle?
Below the threshold value, no action potential is produced | Above the threshold value, the size of the stimulus does not change the size of the action potential
33
How can an organism perceive the size of the stimulus?
The number of impulses in a given time | By having different neurones with a different threshold value
34
What is the refractory period?
The period after the an action potential has been created The inward movement of sodium is prevented because the voltage-gated channels are closed It is impossible for a further action potential to be generated
35
What are the main purposes of the refractory period?
It ensures that action potentials are propogated in one direction only It produces discrete impulses It limits the number of action potentials
36
What is a synapse?
Where one neurone communicates with another or an effector
37
How do synapses transmit information?
By means of chemicals known as neurotransmitters
38
What are neurones seperated by?
A synaptic cleft
39
What is the name of the neurone that releases the neurotransmitter?
The presynaptic neurone
40
What is the general shape of the presynaptic neurone?
The axon ends in a swollen portion known as the synaptic knob
41
What organelles are common in the presynaptic knob?
Mitochondria Large amounts of ER These are required for the manufacture of the neurotransmitter
42
Where is the neurotransmitter stored?
In the synaptic vesicles
43
What are the names of the two neurones in a synapse?
The presynaptic neurone | The postsynaptic neurone
44
Can synapses be used in either direction?
No, one neurone is postsynaptic and one is postsynaptic which means that they only work in one direction
45
What is spatial summation?
Where a number of presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the postsynaptic neurone
46
What is temporal summation?
Where a single presynaptic neurone releases the neurotransmitter many times over a short period to increase the concentration enough to reach the threshold
47
What are the two types of summation?
Temporal and spatial
48
How do inhibitory synapses operate?
The presynaptic neurone releases a type of neurotransmitter that binds to chloride ion protein channels on the postsynaptic neurone The neurotransmitter causes the channels to open Chloride ions move into the postsynaptic neurone by facilitated diffusion The binding causes the opening of nearby potassium channels Potassium moves out of the postsnyaptic neurone into the synapse The overall effect of this causes the inside of the postsynaptic membrane to be more negative This is called hyperpolarisation and makes it less likely for an action potential to be created because a larger influx of sodium is needed to produce one
49
Where is the neurotransmitter in a synapse produced?
Only in the presynaptic neurone
50
How is the neurotransmitter released in the synapse?
The neurotransmitter is stored in the synaptic vesicles When an action potential reaches the synaptic knob, the membranes of these vesicles fuse with the pre-synaptic membrane to release the neurotransmitter
51
What is an excitatory synapse?
Synapses that produce new action potentials when the neurotransmitter binds with the receptor proteins in the postsynaptic neurone
52
What is a cholinergic synapse?
One in which the neurotransmitter is a chemical called acetylcholine
53
Where can cholinergic synapses be found?
In the central nervous system | Neuromuscular junctions between neurones and muscles
54
What is the process of the transmission across a cholinergic synapse?
The arrival of an action potential at the end of the presynaptic neurone causes calcium ion protein channels to open Calcium ions enter the synaptic knob by facilitated diffusion The influx of calcium into the presynaptic neurone causes synaptic vesicles to fuse with the presynaptic membrane, releasing acetylcholine to the synaptic cleft AC diffuses across the synaptic cleft (short diffusion pathway) AC binds to receptor sites on sodium ion protein channels in the membrane of the postsynaptic neurone Sodium ion protein channels open which allows sodium ions to diffuse rapidly along a concentration gradient The influx of sodium generates a new action potential in the postsynaptic neurone Acetylcholinesterase hydrolses AC into choline and ethanoic acid which diffuses back across the synaptic cleft into the presynaptic neurone The breakdown of AC prevents it from being continuously generating an action potential which leads to the discrete transfer of information ATP is used to recombine AC which is stored in synaptic vesicles for future use Sodium ion protein channels close in the absence of AC
55
What is the simplified process of a cholinergic synapse?
The action potential causes Ca2+ channels to open in the presynaptic ending (voltage gated) The influx of calcium causes the synaptic vesicles to fuse with the presynaptic membrane (exocytosis) Acetylcholine neurotransmitter diffuses across the cleft and binds to receptors This causes sodium channels to open which may initiate an action potential if a threshold depolarisation is achieved
56
What does acetylcholinerase do?
It hydrolyses the neurotransmitter acetylcholine The products are used to resynthesise Ach using acetyl coenzyme A from the mitochondria This prevents the channels from being constantly open This inhibits the impulse
57
What is essential to survive?
Being able to sense changes in the environment or stimulus and respond to these changes
58
What is a sense organ?
An organ which has specialised cells that can detect stimulus called receptor cells
59
What is the 2nd stage of stimulus?
Coordination / processing / thinking
60
What are the steps between the stimulus and response?
Receptor: sensory cells Co-ordinator: brain or spinal cord, CNS Effector: muscle or gland
61
What is the purpose of the endocrine system?
It releases hormones in the blood (e.g. insulin)
62
What is the purpose of the exocrine system?
It releases enzymes into specific areas (e.g. saliva)
63
Does the endocrine or exocrine system have a greater effect on the body?
Endocrine (hormones)
64
What are resting potentials created by?
Created by the active transport of Na+ and K+
65
What can a nerve impulse be described as?
A wave of electrical activity
66
What happens to the sodium potassium pump in the axon at rest?
3Na+ ions are pumped out 2K+ ions are pumped in This makes the neurone polarised at rest This is known as an electrochemical gradient
67
What is the resting potential helped by?
Faster K+ diffusion caused by carrier proteins
68
How do K+ ions leak out of the axon during rest?
Down their concentration gradient via a carrier protein | Na+ ions do not do this as the membrane is impermeable to Na+
69
What creates an electrochemical gradient?
There are more sodium ions in the tissue fluid than in the axon, thus creating a gradient
70
What causes an action potential to be generated?
When a stimulus above a certain intensity (threshold) arrives at a receptor or nerve ending
71
When an action potential is first generated, what happens to the membrane potential?
There is a rapid switch in membrane potential from -65mV to +40mV
72
What is a saltatory conduction?
Where Schwann cells form insulation
73
Where does the ion movement occur along the axon?
In the nodes of ranvier because there is no insulation to prevent ion movement
74
Where does action potential occur?
On adjacent nodes of ranvier | This makes it more rapid because the action potential makes jumps along the axon instead of travelling along it

Grice/Hall AQA A-Level Biology Revision Year13 (60 decks)

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