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AQA A Level Biology > 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

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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
Q

What is an action potential?

A

A travelling wave of depolarisation

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26
Q

How does an action potential move along the axon?

A

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

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27
Q

What is a nerve impulse?

A

The transmission of an action potential along the axon of a neurone

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28
Q

What are the three factors which affect the speed at which an action potential travels?

A

Myelin sheath
Diameter of the axon
Temperature

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29
Q

How does the myelin sheath affect the speed at which an action potential travels?

A

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)

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30
Q

How does the diameter of the axon affect the speed at which an action potential travels?

A

The greater the diameter, the faster the speed of conductance
This is due to less leakage of ions

31
Q

How does the temperature of the axon affect the speed at which an action potential travels?

A

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
Q

Why can nerve impulses be described as following the all or nothing principle?

A

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
Q

How can an organism perceive the size of the stimulus?

A

The number of impulses in a given time

By having different neurones with a different threshold value

34
Q

What is the refractory period?

A

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
Q

What are the main purposes of the refractory period?

A

It ensures that action potentials are propogated in one direction only
It produces discrete impulses
It limits the number of action potentials

36
Q

What is a synapse?

A

Where one neurone communicates with another or an effector

37
Q

How do synapses transmit information?

A

By means of chemicals known as neurotransmitters

38
Q

What are neurones seperated by?

A

A synaptic cleft

39
Q

What is the name of the neurone that releases the neurotransmitter?

A

The presynaptic neurone

40
Q

What is the general shape of the presynaptic neurone?

A

The axon ends in a swollen portion known as the synaptic knob

41
Q

What organelles are common in the presynaptic knob?

A

Mitochondria
Large amounts of ER
These are required for the manufacture of the neurotransmitter

42
Q

Where is the neurotransmitter stored?

A

In the synaptic vesicles

43
Q

What are the names of the two neurones in a synapse?

A

The presynaptic neurone

The postsynaptic neurone

44
Q

Can synapses be used in either direction?

A

No, one neurone is postsynaptic and one is postsynaptic which means that they only work in one direction

45
Q

What is spatial summation?

A

Where a number of presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the postsynaptic neurone

46
Q

What is temporal summation?

A

Where a single presynaptic neurone releases the neurotransmitter many times over a short period to increase the concentration enough to reach the threshold

47
Q

What are the two types of summation?

A

Temporal and spatial

48
Q

How do inhibitory synapses operate?

A

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
Q

Where is the neurotransmitter in a synapse produced?

A

Only in the presynaptic neurone

50
Q

How is the neurotransmitter released in the synapse?

A

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
Q

What is an excitatory synapse?

A

Synapses that produce new action potentials when the neurotransmitter binds with the receptor proteins in the postsynaptic neurone

52
Q

What is a cholinergic synapse?

A

One in which the neurotransmitter is a chemical called acetylcholine

53
Q

Where can cholinergic synapses be found?

A

In the central nervous system

Neuromuscular junctions between neurones and muscles

54
Q

What is the process of the transmission across a cholinergic synapse?

A

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
Q

What is the simplified process of a cholinergic synapse?

A

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
Q

What does acetylcholinerase do?

A

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
Q

What is essential to survive?

A

Being able to sense changes in the environment or stimulus and respond to these changes

58
Q

What is a sense organ?

A

An organ which has specialised cells that can detect stimulus called receptor cells

59
Q

What is the 2nd stage of stimulus?

A

Coordination / processing / thinking

60
Q

What are the steps between the stimulus and response?

A

Receptor: sensory cells
Co-ordinator: brain or spinal cord, CNS
Effector: muscle or gland

61
Q

What is the purpose of the endocrine system?

A

It releases hormones in the blood (e.g. insulin)

62
Q

What is the purpose of the exocrine system?

A

It releases enzymes into specific areas (e.g. saliva)

63
Q

Does the endocrine or exocrine system have a greater effect on the body?

A

Endocrine (hormones)

64
Q

What are resting potentials created by?

A

Created by the active transport of Na+ and K+

65
Q

What can a nerve impulse be described as?

A

A wave of electrical activity

66
Q

What happens to the sodium potassium pump in the axon at rest?

A

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
Q

What is the resting potential helped by?

A

Faster K+ diffusion caused by carrier proteins

68
Q

How do K+ ions leak out of the axon during rest?

A

Down their concentration gradient via a carrier protein

Na+ ions do not do this as the membrane is impermeable to Na+

69
Q

What creates an electrochemical gradient?

A

There are more sodium ions in the tissue fluid than in the axon, thus creating a gradient

70
Q

What causes an action potential to be generated?

A

When a stimulus above a certain intensity (threshold) arrives at a receptor or nerve ending

71
Q

When an action potential is first generated, what happens to the membrane potential?

A

There is a rapid switch in membrane potential from -65mV to +40mV

72
Q

What is a saltatory conduction?

A

Where Schwann cells form insulation

73
Q

Where does the ion movement occur along the axon?

A

In the nodes of ranvier because there is no insulation to prevent ion movement

74
Q

Where does action potential occur?

A

On adjacent nodes of ranvier

This makes it more rapid because the action potential makes jumps along the axon instead of travelling along it

AQA A Level Biology (51 decks)

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