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A-Level Biology - OCR A > 5.1.3 Neuronal Communication > Flashcards

5.1.3 Neuronal Communication Flashcards

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1
Q

What is a sensory receptor?

A

A specialised cell that detects a change in our surroundings. A response is brought about when they detect a stimulus.

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2
Q

What are transducers?

A

Molecules that convert one type of energy to another - in the case of neurones to electrical energy.

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3
Q

What is a stimulus?

A

A change in the environment

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4
Q

How do receptors work?

A

They are specially adapted to detect change in a particular form of energy. Whatever the stimulus energy type is it will be converted to electrical to produce an action potential.

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5
Q

Where are sensory receptors found?

A

At the start of sensory neurones

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6
Q

What is the Pacinian Corpuscle?

A

A sensory receptor that detects changes in pressure.

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7
Q

What is the structure of the Pacinian Corpuscle?

A

An oval-shaped structure consisting of concentric rings of connective tissue wrapped around a nerve ending.

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8
Q

How does the Pacinian Corpuscle detect pressure change?

A

When pressure is applied it deforms the shape of the connective tissue which puses against the nerve endings. The Corpuscle is only sensitive to changes in pressure which deforms the rings. So if the pressure is constant they stop responding.

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9
Q

What happens in the Pacinian Corpuscle when pressure change is detected?

A

Stretch-mediated sodium channels change shape and open. This increases sodium permeability so sodium ions flood the membrane. This depolarises the membrane and creates a generator potential. After the concentric rings of connective tissue voltage-gated channels open to allow more sodium ions in.

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10
Q

What is a neurone?

A

The cell by which a nervous impulse is transmitted across the body.

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11
Q

What are the 3 types of neurones? .

A

Sensory, Relay and Motor

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12
Q

What does a sensory neuron do?

A

Carries an action potential from the receptor to the CNS

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13
Q

What is the structure of a senory neurone?

A

TO DO

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14
Q

What is a relay neurone?

A

Many short axons that connect the sensory neurone and motor neurone

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15
Q

What is the relay neurone also known as?

A

The inner neurone

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16
Q

What is the structure of the relay neurone?

A

TO DO

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17
Q

What is the motor neurone?

A

Carries the action potential from te relay neurone (in the CNS) to the effector

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18
Q

What is an effector?

A

A gland or muscle that carries out a responce.

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19
Q

What is the structure of a motor neurone?

A

TO DO

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20
Q

What are myelenated and unmyelenated neurones?

A

Neurones that have a myelenated sheath or dont.

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21
Q

NEED MORE ON MYELENATION

A

TO DO

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22
Q

When are neurones at rest?

A

When they are not transmitting an acton potential

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23
Q

What happens in the neurone when at rest?

A

Sodium ion channels are kept cloed with some otassium channels open. Sodium/potssium pumps use ATP to activley pump 3 sodium ions out of the cell and 2 potassium ions into the cell

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24
Q

Why does this happen at rest?

A

to maintain the cell at a negitive potential compared to outside of the cell. Making the cell polarised.

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25
Q

What is the resting potential of a neurone?

A

-70mV

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26
Q

How is a generator potential produced?

A

In responce to a stimulus gated sodium channels open (Strech mediated in the Pacinian Corpuscle). This allows sodium ions to quickly diffuse down the concentration greadient into the membrane from the surrounding tissue fluid. Ths produces a small depolorisation of the membrane called the generator potential.

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27
Q

What happens to the generator potential?

A

Doesnt travel down the neurone and continues to increase as it continues to depolorise the membrane untill it reaches the threshold value.

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28
Q

What is the threshold value? (Definition)

A

The ammound of depolarisation needed to open the voltage gated channels.

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29
Q

What is the threshold value? (Value)

A

-50mV

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30
Q

What happens whn the threshold value is reached?

A

Voltage gated sodium channels open and allow a further influx of sodium ions into the membrane.

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31
Q

Why is it called the all or nothing law?

A

If the threshold vlaue is met then further depolorisation occours. If it is not then the gated channels dont open. There is no middle ground.

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32
Q

How is the threshold value and the all or nothing law an example of positive feedback?

A

The small depolorisation created by the generator potential is further depolarised. Small potential becomes larger.

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33
Q

What happens after the voltage gated channels open?

A

The increase in sodium ions continues to depolarise the the inside of the cell to +40mV. This allows an action potential to be transmitted along the neurone.

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34
Q

What happens to the channels at +40mV?

A

Sodium channels close and voltage gated potassium channels open. Potassium ions diffuse out of the cell and bring the potential difference back to negitive and the resting potential after hyperpolarising the membrane.

35
Q

What is the full process for the generation of an action potential?

A
  1. Membrane starts at a resting potential of -70mV. A stimulus is detected and sodium ion channlels open, sodium ions diffuse into the cell. The membrane depolarises and reaches the threshold value of -50mV. 2. This causes voltage gated sodium ion channels to open so more sodium ions diffuse in and the cell becomes positivly charged. 3. The potential reaches +40mV causing sodium channels to close and potasium channels to open. 4. potassium ions move out of the cell to bring the potential difference back to negitive. 5. The cell hyperpolarises to -75mV as the potential difference overshoots slightly. 6. The original potential difference is restored so the cell returns to its resting state of -70mV.
36
Q

What is the refactory period?

A

The period of hyperpolarisation between -75mV and -70mV. During this short period of time it is impossible to stimulate the cell membrane to generate another action potential.

37
Q

Why is there a refactory period?

A

Allows the cell to recover after an action potential e.g. regenerate ATP. It also ensures that action potentials are only sent in one direction.

38
Q

What happens in the refactory period?

A

As sodium and potassium ions are in the wrong place (wrong side of the cell) they must be activly pumped by sodium/potassium channels to restore the gradients.

39
Q

What is the ratio for sodium/potassium pumps?

A

3 Na+ are pumped out of the cell for every 2 K+ that are pumped into the cell.

40
Q

What is local current?

A

The movement of sodium ions alof the cell from the region of high concentration to a region of lower cconcentration.

41
Q

What effect does the local current have?

A

Causes the depoloriseation to continue accross the cell so more voltage gated sodium ion channels open and the ions move into the cell. This continues the action potential.

42
Q

What is local current an example of?

A

Positive feedback. A small depolorisation somewhere is exhemplified.

43
Q

What is the process of a local current?

A

An action potential occours whrn a sodium channel opens. This allows sodium ions to diffuse accross the membrane from high concentration outsidfe the cell and to the lower one indside the cell. Increasign the concentration of sodium ions where the channel opens. sodium ions diffuse alonfg the neurone away from the region of increased concentration. This is the local current. Ths causes depolorisation further down the membrane makign more sodium ion channels open so more sodium ions enter and continue the action potential.

44
Q

What about the structure of a neurone prevents the diffusion of sodium ions?

A

The myelin sheath (a fatty layer made of schwann cells) does not have sodium channels so sodium ions cant diffuse through.

45
Q

Where in the structure can can sodium ions diffuse into the structure?

A

At the nodes of ranvier - the gaps between the sections of the sheath. The nodes contain channel proteins that allow sodium ions to diffuse accross the membrane.

46
Q

What effect does the node of Ranvier have on the action potential?

A

It elongates the local current across the myelinated sheath. New action potentials are only made at the nodes so it is said that the action potential ‘jumps’ from one node to the next.

47
Q

What is the apparent ‘jumping’ of action potentials called?

A

Saltatory Conduction

48
Q

What are the advantages of saltatory conduction?

A

Speeds up the rate of transmission across the membrane.

49
Q

Do myelinated or non myelinated tissue have a quicker rate of conduction?

A

Myelinated - due to the ‘jumping’ of potentials.

50
Q

How are the intensities of a stimulus indicated?

A

The frequency of action potentials reaching the brain. A more frequent action potential indicates a more intense stimulus. All action potentials are the same intensity and produce the same depolorisation. (+40mV).

51
Q

What happens in the cell when a stimulus is higher?

A

More sodium ion channels are opened so more generator potentials are generated to create more action potentials.

52
Q

What effects the speed of transmission through a neurone?

A

Diameter of the axon. Myelenation.

53
Q

How does the diameter of the axon effect the speed of transmission?

A

Larger diameters have higher transmission speeds as there is reduced resistance.

54
Q

How does myelination effect the speed of transmission?

A

Myelination increases the velocity of the action potential by saltatory conduction.

55
Q

What is a synapse?

A

The junction between two neurons.

56
Q

What is the structure of the synapse?

A

At the end of one neuron (the presynaptic neuron) is a presynaptic bulb. At the start of the next neuron (the postsynaptic neuron) is the post synaptic bulb. The bulbs do not touch and the gap between them is called the synaptic cleft.

57
Q

What happens in the Synaptic Cleft?

A

Neurotransmitters diffuse accross the cleft from the presynaptic bulb to the postsynaptic bulb.

58
Q

What is the name of the neurotransmitter typically used?

A

Acetylcholine

59
Q

What are synapses called that use acetylcholine?

A

Cholinergic synapses

60
Q

What is the structure of the presynaptic bulb?

A

A swelling at the end of the presynaptic neuron. It is specialised by having: *lots of mitochondria - for active processes requiring ATP. *Lots of smooth endoplasmic reticulum - for packaging neurotransmitters into vesicles. *Lots of vesicles that contain neurotransmitters. *Lots of voltage gated calcium ion channels on the cell surface membrane.

61
Q

What is the structure of the postsynaptic membrane?

A

Contains specialised sodium ion channels that respond to neurotransmitters.

62
Q

What is the structure of the sodium ion channels?

A

Formed of 5 polypeptide molecules, two of which have a receptor site for acetylcholine.

63
Q

What happens to the receptor/channel during transmission?

A

When acetylcholine is pressent in the cleft it binds to the receptor site and causes the sodium ion channels to open.

64
Q

During a transmission across a synapse, what happens in the presynaptic bulb?

A

1) an action potential arrives at the presynaptic bulb and depolorises the membrane. 2)This causes voltage gated calcium ion channels to open and calcium ions to diffuse into the presynaptic bulb. 3)They bind to synaptic vesical containing neurotransmitters causing the vesical to move to and fuse to the cell surface membrane. 4)Acetylcholine is released into the synaptic cleft by exocytosis?

65
Q

During a transmission across a synapse, what happens in the synaptic cleft?

A

Acetylcholine diffuses across the cleft. They bind to receptor sites on the sodium ion channels and cause them to open.

66
Q

During a transmission across a synapse, what happens in the postsynaptic membrane?

A

The sodium ion channels open in response to acetylcholine allowing sodium ions to diffuse into the postsynaptic neuron. This depolorises the neuron and creates an Excitatory Post Synaptic Potential (EPSP). These combine to meet the threshold value and create a new action potential in the post synaptic neuron. The action potential is sent down the neuron.

67
Q

Why is it important to remove the acetylcholine from the synaptic cleft?

A

Otherwise it will always bind to the sodium ion channels and keep them perminantly open. This will continue to create action potentials in the post synaptic neuron.

68
Q

What is used to remove acetylcholine from the synaptic cleft?

A

The enzyme acetylcholinesterase

69
Q

What does acetylcholinesterase do?

A

Hydrolises acetylcholine into ethanoic acid (acetic acid) and choline. This stops AC binding with channels and creating more action potentials.

70
Q

What happens to the products from hydrolysis of acetylcholine?

A

Ethanoic acid and and choline are passed back into the presynaptic bulb by diffusion. They are then recycled by recombining the molecules, using ATP, to produce acetylcholine which is stored in synaptic vesicles to be used again.

71
Q

What is the issue with the potential generated in the post synaptic neuron?

A

It is not great enough to meet the threshold value and regenerate the action potential.

72
Q

How can the threshold value be created in the postsynaptic neurone?

A

By creating multiple potentials which add up to meet the threshold value.

73
Q

What is the adding of potentials called?

A

Summation

74
Q

How can summation be used to create the threshold value?

A

Sending the action potential down multiple dendrites. Sending multiple waves of the action potential down the same dendrite.

75
Q

Where else can action potentials come from?

A

Other neurons that all have endings on the same neuron. The potentials from all the neurons can summate to create a threshold value.

76
Q

What is temporal summation?

A

Multiple action potentials sent over the same dendrite/from the same neuron. They arrive in rapid succession and can summate to meet the threshold value to create the action potential. The potential created in each wave lasts a few milliseconds which allows it to be added to other waves that follow it.

77
Q

What is spacial summation?

A

Multiple dendrites or neurons coming to the next cell at the same time. Either from different neurons or down different dendrites. This means that more neurotransmitters are released so there is more depolorisation within the neuron to meet the threshold value and produce an action potential.

78
Q

What is an EPSP

A

Excitatory Post Synaptic Potential. Depolorises the membrane

79
Q

What are examples of neurotransmitters that cause EPSPs?

A

Acetylcholine

80
Q

What is an IPSP?

A

Inhibitory Post Synaptic Potential. Hyperpolorises the membrane.

81
Q

What are examples of neurotransmitters that cause IPSPs?

A

GABA, Glycine, Serotonin, Dopermine

82
Q

What happens if IPSPs and EPSPs arrive at the same time?

A

They cancel out each others effects. This means that an increased number of EPSPs may be needed to reach the threshold value.

83
Q

CONTROL OF COMMUNICATION

A

NEEDS DONG BRO

A-Level Biology - OCR A (16 decks)

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