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Neurology > Week 2- pharmacology > Flashcards

Week 2- pharmacology Flashcards

1
Q

What is an axon hillock?

A

Where the axon emerges from the cell body.

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2
Q

Other name for cell body of a neurone?

A

Soma

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3
Q

What is the function of dendrites?

A

They receive inputs from other neurones and convey them towards the cell body.

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4
Q

What is the function of the soma (cell body)?

A

It contains mitochondria and Nissl substance (exactly the same as RER)- energy production of the neurone.
Also conveys incoming signals to the axon hillock.

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5
Q

At what site in the neuron does initiation of the ‘all or nothing’ response occur?

A

The axon hillock.

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6
Q

Function of the axon

A

Conducts output signals as action potentials to other neurones

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7
Q

What is a synapse?

A

Point of chemical communication between neurones.

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8
Q

How can neurones be classified?

A

As the number of neurites (processes coming directly off the cell body) it has.

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9
Q

Describe a unipolar neuron?

A

Has one neurite coming off the cell body. The axon may split into branches further down.

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10
Q

Describe a psuedounipolar neuron?

A

Has one neurite that bifurcates (splits).

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11
Q

Describe a bipolar neuron?

A

Has two neurites originating from the cell body.

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12
Q

Describe a multipolar neuron?

A

Has three or more neurites coming from the cell body

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13
Q

Where in the body would you find a unipolar neuron (generally)?

A

Peripheral autonomic neuron (e.g. sympathetic, parasympathetic)

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14
Q

Where in the body would you find a psuedounipolar neuron?

A

Dorsal root ganglion neuron

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15
Q

Where in the body would you find a bipolar neuron?

A

Retinal bipolar neuron

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16
Q

Where in the body would you find a multipolar neuron?

A

Lower motor neuron

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17
Q

what are the four functional regions of the neurone?

A

Input, integrative, conductile, output

Input being the dendrites, integrative being the soma, conductive being the axon and output being the synapse.

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18
Q

What is the value of resting potential in neurones?

A

-70mv

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19
Q

What is the value of threshold?

A

-60mV

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20
Q

Describe how an AP is initiated (using channels) in an axon?

A

Depolarising stimulus arrives opening a few sodium channels. If the depolarising stimulus is large enough (to reach threshold potential), then lots more voltage gated sodium channels will open allowing a massive influx into the axon. This means the membrane potential moves from about -70 to +40. The period that the axon is positively charged (before the potassium channels open) is called overshoot. Then the potassium channels open allowing K+ to move out of the axon bringing the membrane potential down to about -90mv. This is called the undershoot. The sodium and potassium channel then restore the membrane potential to -70mV.

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21
Q

What two factors have an effect on speed of conduction?

A

Myelination

Diameter of the axon

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22
Q

What factors would stop current from leaking out of the axon?

A

Myelination- keep the axon insulated or

Increase external resistance. As you increase the external resistance, the current loss to the environment decreases.

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23
Q

What is the relationship between the length constant and current spread?

A

The bigger the length constant, the further the current will spread.

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24
Q

How is a local current set up within the axon?

A

As the axon is positive (depolarised)- the part of axon next to it will be negative (resting potential). Opposite charges attract and therefore sets up a local current. This means that before even the action potential arrives- the membrane infront of it has started to become depolarised.

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25
Q

What factors could increase current speed along the axon?

A 
Decreasing Ri (internal resistance of the axoplasm)- this could be by making the axons diameter larger. 
Increasing Rm (external resistance)- possibly by adding an insulating material.
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26
Q

What syndrome is caused by failure of myelination in the CNS?

A

Multiple sclerosis

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27
Q

What syndrome is caused by failure of myelination in the PNS?

A

Guillian Barre syndrome

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28
Q

What is saltatory conduction?

A

The AP jumps from one Node of Ranvier to the next. This is because the myelin sheath stops any current being lost.

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29
Q

What is an axodendritic synapse?

A

A synapse between (presynaptically) a dendrite, and (postsynaptically) a axon.

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30
Q

What is an axosomatic synapse?

A

A synapse between (presynaptically) the soma and (postsynaptically) an axon

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31
Q

What is an axoaxonic synapse?

A

Axon to axon.

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32
Q

How can synapses be classified functionally?

A

Excitatory or inhibitory

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33
Q

Which excitatory transmitter is used most frequently in the CNS?

A

Glutamate

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34
Q

Which inhibitory transmitter is used most frequently in the CNS?

A

GABA or glycine.

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35
Q

What is the difference between inhibitory and excitatory neurotransmitters action on the postsynaptic membrane?

A

Excitatory neurotransmitters activate cation channels whereas inhibitory activate anion channels.
Inhibitory ones hyper polarise the cell (taking it even further away from resting potential) whereas excitatory ones depolarise the cell closer to threshold.

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36
Q

What is an excitatory postsynaptic potential (epsp)?

A

A local, graded depolarising response.

37
Q

What is an inhibitory postsynaptic potential (ipsp)?

A

A local graded, hyper polarising response.

38
Q

Describe the process at the post-synaptic membrane when an excitatory neuron releases neurotransmitter into the synaptic cleft?

A

Neurotransmitter (glutamate) binds to glutamate receptors on the postsynaptic membrane. This activates sodium selective ion channels. The sodium channels can then briefly open allowing an influx of sodium into the axon. If the influx reaches threshold, an AP will start.

39
Q

Describe the process at the post-synaptic membrane when an inhibitory neuron releases neurotransmitter into the synaptic cleft?

A

Neurotransmitter (GABA or glycine) binds to receptors on the post-synaptic membrane. This activates chloride channels and chloride moves into the axon, further depolarising it.

40
Q

How can epsp’s and ipso’s affect each other?

A

To one neuron, there will be several synaptic connections. If two epsp’s and one ipsp are going to the same neuron- the net effect will be excitatory because the two epsp’s add up minus the one ipsp.

41
Q

Describe the process of synaptic transmission in the neuron.

A

Precursor for the neurotransmitter is brought into the cell
The neurotransmitter is then synthesised.
It is then stored in vesicles
An action potential arrives causing depolarisation
Calcium influx into the cell
Vesicles fuse with presynaptic membrane
Neurotransmitter is released into the synaptic cleft.

42
Q

Which neurotransmitters do not come in every cell and have to be synthesised?

A

GABA and amines.

43
Q

Which neurotransmitters come in every cell and have to be synthesised?

A

Glycine and glutamate occur in all cells.

44
Q

Where are the enzymes that catalyse the synthesis of neurotransmitter made and how do they get to the terminal bouton?

A

They are made in the cell body and transported in microtubules to the terminal bouton. Here they carry out their function of making neurotransmitter.

45
Q

How are neurotransmitters made?

A

The precursor protein is synthesised in the RER. It is in then cleaved in the Golgi apparatus. Secretory granules then bud off from the Golgi apparatus. Secretory granules are transported to the presynaptic terminal by microtubules.

46
Q

What are proprioceptive sensations?

A

Concerning posture and movement.

47
Q

What are exteroceptive sensations?

A

Cutaneous senses from the surface of the body.

48
Q

What are visceral sensations?

A

Specifically from internal organs.

49
Q

What are deep sensations?

A

From the fascie, muscles and bone.

50
Q

How does a stimulus in the environment turn into chemical activity?

A

The stimulus; which can be mechanical, thermal or chemical, open a cation selective ion channel in the nerve ending eliciting a depolarising effect.
The amplitude of the potential is graded and in proportion to the stimulus intensity. E.g. if someone punches you it will create a bigger potential than if someone taps you.
IF it reaches the threshold, an AP will occur.

51
Q

Describe muscle spindles response to stretch

A

The muscle becomes stretched and therefore so do the spindle cells lying in the muscle belly. The stretching causes them to fire AP’s. The more they are stretched, the more they fire. As the stimulus duration increases- so does the duration of the APs

52
Q

What is meant by the term modality?

A

The principle type of stimulus that is transducer into an electrical signal in a primary afferent neurone.
AKA a stimulus the receptors will respond too.

53
Q

What do low threshold mechanoreceptors mediate and what is meant by ‘low threshold’?

A

They mediate touch, vibration and pressure. Low threshold means that they respond to low intensity stimulus (non-damaging and non painful).

54
Q

What do low threshold thermoreceptors mediate?

A

Cold, cool, indifferent, warm and hot.

55
Q

What do high threshold units respond too?

A

Respond to high (noxious and potentially damaging) stimuli.

56
Q

Which receptor picks up touch, pressure and vibration?

A

Skin mechanoreceptors

57
Q

Which receptor picks up proprioceptive stimuli?

A

Joint and muscle mechanoreceptors

58
Q

Which receptor picks up thermal stimuli?

A

Hot and cold thermoreceptors

59
Q

Which receptor picks up painful stimuli?

A

Mechanical, thermal and polymodal nociceptors

60
Q

Which receptor picks up itchy stimuli?

A

Itch receptors.

61
Q

What do high intensity mechanoreceptors respond to?

A

High intensity mechanical stimulus

62
Q

What do high intensity thermal receptors respond to?

A

Extreme degrees of heat >45 degrees

<10-15 degrees.

63
Q

What do high intensity chemical nociceptors respond to?

A

Substances in tissue (as found in inflammation)- prostaglandins, bradykinin, serotonin, histamine, K+, H+, ATP.

64
Q

What do polymodal nociceptors respond to?

A

Atleast 2 of what high intensity chemical, thermal or mechanoreceptors respond too.

65
Q

What is adaption in the context of primary sensory neurones?

A

A feature of primary sensory neurones where they can either change their firing rate only in response to a stimulus of varying intensity or fire continuously throughout a constant stimulus.

66
Q

What is a slowly adapting tonic/static response?

A

When a stimulus slowly increases in intensity, so does the rate of firing of APs
When a stimulus suddenly increases to a constant intensity, the rate of APs is constant.

67
Q

What is a rapidly adapting phasic/dynamic response?

A

When a stimulus slowly increases- the APs are only firing when the stimulus intensity is changing. When it reaches a constant intensity, the APs stop.

68
Q

What is a very rapidly adapting phasic/dynamic response?

A

When a stimulus is very rapid it will send out action potentials, but other than that it will not react.

69
Q

Give an example of a slowly adapting response receptor?

A

Stretch receptors

70
Q

Give an example of a rapidly acting response receptor?

A

Muscle spindles

Hair follicle afferents

71
Q

Give an example of very rapidly adapting response receptors?

A

Pacinian corpuscles.

72
Q

What is the receptive field of a neurone?

A

The region that when stimulated with an adequate stimulus will cause a response in that neurone.

73
Q

In primary afferent neurons, where is the receptive field?

A

At the terminal end of the neurone.

74
Q

In the skin, RF’s overlap. True or false?

A

True.

75
Q

How do receptive fields explain the point discrimination ability of different types of the body?

A

The smaller the RF in that area of the body, the easier it will be to distinguish two points that are stimulated in that area.

76
Q

Where in the body has lots of small RF’s? What does this mean for two point discrimination.

A

The hands have lots of receptive fields. Two point discrimination is when you can tell the difference between two points fairly close together. If they are both in one receptive field then you won’t be able to distinguish between them. However if they are in different receptive fields you will be able too. Therefore more and smaller receptive fields means a better two point discrimination.

77
Q

Where are Meissners corpuscles abundant?

A

In the skin. And in places where two point discrimination is highest.

78
Q

What do Meissners corpuscles respond to?

A

Vibration.

79
Q

What do pacinian corpuscles respond to?

A

Pressure.

80
Q

Where are Merkel discs most abundant?

A

In hairy skin. Also kind of follow the same pattern as Meissners.

81
Q

Where are Krause end bulbs found?

A

At the border of dry skin and mucous membranes.

82
Q

Where are Ruffini endings found?

A

Within the dermis and joint capsules.

83
Q

Where are Pacinian corpuscles found?

A

Within dermis and fascia.

84
Q

What sort of fibres (e.g. SA, RA, or very rapidly adapting) fibres do Meisnners corpuscles detect? Also what sort of stimulation do they respond too?

A

RA.

Respond to pressure e.g. stroking, fluttering.

85
Q

What sort of fibres (e.g. SA, RA, or very rapidly adapting) fibres do Merkel discs detect? Also what sort of stimulation do they respond too?

A

SA

Pressure, texture.

86
Q

What sort of fibres (e.g. SA, RA, or very rapidly adapting) fibres do Pacinian corpuscles detect? Also what sort of stimulation do they respond too?

A

Very rapidly adapting

Vibration

87
Q

What sort of fibres (e.g. SA, RA, or very rapidly adapting) fibres do Ruffini endings detect? Also what sort of stimulation do they respond too?

A

SA

Skin stretch.

88
Q

Pacinian corpuscles have much larger RFs than Meiseners corpuscles. T or F?

A

True.

Neurology (19 decks)

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