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Biology mod 5 Communication, homeostasis and energy > 5.1.3 Neuronal communication > Flashcards

5.1.3 Neuronal communication Flashcards

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1
Q

What are neurones?

A

Specialised cells which carry electrical impulses around the body.

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2
Q

What are bundles of neurones known as?

A

Nerves

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3
Q

Give some features present in all neurones.

A

-Axon
-A cell body
-A dendrite

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4
Q

What is found at the end of an axon?

A

An axon terminal which contains may nerve endings which allow neurones to connect to many other neurones and receive impulses from them.

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5
Q

What does it mean if a neurone is myelinated?

A

Their axon is insulated by a myelin sheath.

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6
Q

What are the small uninsulated sections of the myelin sheath called?

A

Nodes of Ranvier.

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7
Q

Purpose of the nodes of ranvier.

A

Electrical impulses do not have to travel along the whole axon and instead jump from one node to the next. Less time is wasted transferring the impulse from one cell to another.

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8
Q

Purpose of schwann cells.

A

Surround the axon to provide insulation as they are rich in myelin.

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9
Q

Are impulses faster in myelinated or non-myelinated neurones?

A

Myelinated

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10
Q

What are the three types of neurone?

A

Sensory, motor, relay.

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11
Q

Where are sensory neurones found?

A

Sensory organs.

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12
Q

Function of sensory neurones.

A

Carry impulses from receptors in sensory organs to the CNS.

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13
Q

Features of a sensory neurone.

A

-Dendron which carries impulses to the cell body.
-Axon which carries impulses away from the cell body.
-Cell body
-dendrite

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14
Q

Do dendrons carry impulses to or away from the cell body?

A

To the cell body

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15
Q

Do axons carry impulses to or away from the cell body.

A

Away from the cell body.

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16
Q

Where are relay neurones found?

A

The central nervous system.

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17
Q

Purpose of relay neurones.

A

Connect sensory and motor neurones.

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18
Q

Features of relay neurone.

A

-axon
-dendrites
-cell body

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19
Q

Function of motor neurones.

A

Carry impulses from the CNS to the effectors (muscles or glands)

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20
Q

Features of motor neurones.

A

-Large cell body
-Dendrites which are highly branched
-Axon

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21
Q
A
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22
Q

How do you tell the difference between a sensory and motor neuron?

A

The sensory neurons cell body protrudes outwards whereas the motor neurons cell body is on the dendrite end. Motor neurons have long contrinous axons whereas sensory neurons have shorter axons which are split into two branches.

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23
Q

What is the function of the cell body?

A

The cell body processes the information from the dendrites and produces neurotransmitters

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24
Q

What is the function of dendrites?

A

Dendrites recieve information from other neurons and divert information towards the cell body.

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25
Q

What is the function of the axon?

A

Axons carry electrical impulses across the neuron and cause the neurotransmitters from the cell to be released.

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26
Q

Function of synaptic knobs.

A

Release neurotrasmitters.

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27
Q

Name the cells that respond to stimuli.

A

Receptor cells.

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28
Q

What do receptor cells do?

A

Convert energy from one form e.g light, heat, sound into an electrical impulse to be sent along a sensory neurone.

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29
Q

Where are Pacinian corpuscles found?

A

Deep in the skin e.g skin of fingers, soles of feat.

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30
Q

What do pacinian corpuscles respond to?

A

Changes in pressure.
Receptors stimulated by pressure on the skin.

31
Q

What is it called when an action potential jumps from node to node?

A

Salatory conduction.

32
Q

What is it called when different types of stimuli are converted into electrical impulses?

A

A tranducer.

33
Q

What do photoreceptors detect?

A

Light

34
Q

What do thermoreceptors detect?

A

Heat

35
Q

What do mechanoreceptors detect?

A

Pressure

36
Q

A pacinian corpuscle is an example of a ___receptor. Why?

A

Mechanoreceptor.
it detects pressure changes.

37
Q

Where are pancinian corpuscles found?

A

The ends of sensory neurone axons.

38
Q

Structure of a pacinian corpusule.

A

They have many layers of membrane around the neurone ending containing stretch-mediated sodium ion channels and between the membrane layers is gel containing sodium ions.

39
Q

Function of the sodium ion channels found in the membrane of pacinian corpuscles?

A

The ion channels open when pressure is applied and allow sodium ions to enter. If enough sodium ions diffuse in, an action potential will be generated.

40
Q

What happens when there is no pressure on the pacinian corpusule?

A

Stretch mediated sodium ion channels are too narrow to open so sodium remains outside of the membrane and resting potential is maintained.

41
Q

What happens when the pacinian corpuscles detect that pressure is applied?

A

The layers of the membrane are distorted so the stretch-mediated sodium ion channels will open and sodium ions will enter the axon of the sensory neurone. This influx of sodium ions changes the potential of the axon which causes depolarisation of the membrane, if enough generator potential is produced, an action potential will be established.

42
Q

What is a resting potential?

A

When there is a difference between the electrical charge inside and outside of the neurone.

43
Q

Does the inside or outside of an axon always have a positive charge? Why?

A

Outside.
There are more positive ions outside of the cell than inside (sodium and potassium)

44
Q

What is the usual resting potential number?

A

-70mV

45
Q

How is resting potential created and maintained?

A

Sodium potassium pumps use ATP to move 3 sodium ions out of the neurone for every 2 potassium ions into the neurone which creates an electrochemical gradient but the membrane is not as permable to sodium ions so they cannot diffuse back in. More potassium ions continue to diffuse out but so there is a higher charge on the outside resulting in a -70mV charge inside.

46
Q

What is resting potential created and maintained by?

A

Sodium potassium pumps and potassium ion channels.

47
Q

What causes an action potential?

A

The rapid movement of sodium and potassium ions across an axon membrane.

48
Q

What is an action potential?

A

When a neurones voltage increases beyond a set point from the resting potential and a nervous impulse is generated.

49
Q

Explain the process of an action potential,

A

1) A stimulus triggers sodium ion channels to open allowing sodium ions to diffuse into the neurone down an electrochemical gradient. The potential difference inside and outside of the neurone must reach around -55mv to trigger depolarisation.
2) When the -55mv threshold is reached, an action potential is stimulated and voltage-gated sodium ion channels open. This movement of sodium ions reduces the potential difference as the inside of the axon becomes less negative. This triggers more channels to open, allowing more sodium ions to enter. The axon potential will reach around +30mV.
3) Very shortly after, all the voltage-gated sodium ion channels close therefore stopping any further sodium ions diffusing into the axon.
Voltage gated potassium ion channels now open which allows the diffusion of potassium ions out of the axon which returns the potential difference to -70mV.
4) Potassium ion channels are slow to close which results in too many potassium ions diffusing out of the neurone which causes a period of hyperpolarisation which means the potential difference across this section of the axon membrane becomes more negative than the resting potential.
Once the voltage-gated potassium channels are closed, the resting potential is restored.

50
Q

How do action potentials move?

A

Along the neurone as a wave of depolarisation.

51
Q

What is the ‘all-or-nothing’ principle?

A

An impulse is only transmitted if the initial stimuli is sufficient to increase the membrane potential above a threshold potential.

52
Q

Explain the all or nothing principle?

A

When receptors are stimulated and the stimulus is very weak or below the threshold for depolarisation, the receptor cells will not be sufficiently depolarised and the sensory neurone will not be activated. If the stimulus does reach the threshold potential, then this will stimulated the sensory neurone.

53
Q

Does a bigger stimulus cause a bigger action potential?

A

No, it just causes the neurone to fire more frequently.

54
Q

Why do action potentials move along the axon?

A

After part of the axon has been stimulated, there is a recovery (refractory) period so the depolarisation moves along.

55
Q

What are the three factors affecting the speed of conduction along a neurone?

A

Myelination
Diameter
Temperature

56
Q

Explain why myelinated speeds up the rate of conduction along a neurone.

A

By insulating the axon membrane with the myelin sheath, the speed at which action potentials can travel increases due to the presence of the nodes of Ranvier. Sodium ion channels are concentrated at the nodes which the action potentials jump from one node to the next (saltatory conduction). This allows the impulse to travel much faster. In non-myelinated neurones, the impulse travels as a wave along the whole length which is slower.

57
Q

Explain why in unmyelinated neurones, the speed of conduction is slow?

A

Depolarisation must occur along the whole membrane of the axon.

58
Q

Where along the neurone are sodium ion channels concentrated?

A

The nodes of Ranvier.

59
Q

Explain how diameter affects the speed of conduction along a neurone.

A

An impulse will be conducted at a higher speed along neurones with thicker axons compared to those with thinner axons as Thicker axons have an axon membrane with a greater surface area over which the diffusion of ions can occur which increases the rate of diffusion of sodium and poassium ions which therefore increases the depolarisation rate.

60
Q

Explain how temperature affects the speed at which impulses are conducted along a neurone.

A

Colder conditions can slow down the conduction of nerve impulses as there is less kinetic energy for the facilitated diffusion of potassium and sodium ions.

61
Q

What is a synapse?

A

A junction where two neurones meet.

62
Q

Features of a synapse.

A

-Pre-synaptic neurone
-Synaptic cleft
-Post-synaptic neurone.

63
Q

Explain transmission at a synapse.

A

When an electrical impulse arrives at the end of an axon on the presynaptic neurone, chemical messengers called neurotransmitters are released from vesicles at the presynaptic membrane. The neurotransmitters diffuse across the synaptic cleft and temporarily bind with receptor molecules on the post synaptic membrane. This stimulates the postsynaptic neurone to generate an electrical impulse that travels down the axon of the postsynaptic neurone. The neurotransmitters are then destroyed or recycled.

64
Q

Name one of the key neurotransmitters used in the nervous system.

A

Acetylcholine.

65
Q

What are synapses which use acetylcholine as a neurotransmitter called?

A

Cholinergic synapses.

66
Q

Explain how a cholinergic synapse works.

A

1) The arrival of an action potential at the presynaptic membrane stimulates the voltage-gated calcium ion channel proteins to open.
2) Calcium ions diffuse down an electrical chemical gradient from the tissue fluid surrounding the synapse into the synaptic knob where there is a low concentration of calcium ions.
3) This stimulates ACh- containing vesicles to fuse with the presynaptic membrane and therefore releasing ACh molecules into the synaptic cleft by exocytosis.
4) The ACh molecules diffuse across the synaptic cleft and temporarily bind to the cholinergic receptors in the postsynaptic membrane.
6) This causes sodium ion channels to open.
7) Sodium ions diffuse into the cytoplasm of the postsynpatic neurone.
8) The sodium ions cause depolarisation of the post-synpatic membrane, restoring the electrical impulse once the threshold is reached.
9) The ACh molecules are broken down and recycled which prevents the sodium ion channels from staying permanently open.
10) The enzyme acetylcholinesterase catalyses the hydrolysis of the ACh molecules.
11) The choline is absorbed back into the presynaptic membrane and reacts with acetyl coenzyme A to form ACh which is then packed into vesicles.

67
Q

Synapses can either be _____ or ______

A

Excitatory
Inhibitory

68
Q

What is an excitatory synapse?

A

When neurotransmitters depolarise the postsynaptic membrane making it fire if the action potential threshold is reached.

69
Q

What is an inhibitory synapse?

A

When neurotransmitters hyperpolarise the membrane therefore stopping it from firing.

70
Q

What is summation?

A

The rapid build-up of neurotransmitters in the synapse to help to generate an action potential.

71
Q

What are the two types of summation?

A

Spatial summation
Temporal summation

72
Q

Define spatial summation.

A

When neurones converge to collectively trigger a new action potential as the small amount of neurotransmitter released from each neurone could be enough to reach the threshold potential.

73
Q

Define temporal summation.

A

Where one neurone releases neurotransmitters repeatedly over a short period of time to add up to enough to exceed the threshold value.

Biology mod 5 Communication, homeostasis and energy (8 decks)

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