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BM213: Introduction to Pharmacology > Block D Lecture 3: CNS Sensory Reception and Pain > Flashcards

Block D Lecture 3: CNS Sensory Reception and Pain Flashcards

1
Q

What are the 6 sensory systems?

A

Vision
Somatic sensory (touch)
Gustatory (taste)
Olfaction (smell)
Auditory (hearing)
Proprioception (balance / movement)
(Slide 2)

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2
Q

What 3 things does sensory reception do?

A

Maintains homeostasis
Detects and reacts to changes in the environment
Protects body from noxious (damaging) stimuli
(Slide 3)

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3
Q

What are 3 types of sensory receptors?

A

Cutaneous
Proprioceptors
Special senses (smell, sight etc.)
(Slide 6)

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4
Q

What are 4 subclasses of cutaneous receptors?

A

Chemical pain
Temperature (thermal pain)
Pressure (mechanical pain)
Touch receptors
(Slide 6)

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5
Q

What do proprioceptors do?

A

Provide information about the position, movement and orientation of body parts in space
(Slide 6)

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6
Q

Where are cutaneous and proprioceptors located?

A

Cutaneous receptors are located in the skin whereas proprioceptors are located in muscle
(Slide 6)

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7
Q

What fibres do chemical, temperature, pressure, touch and body position (proprioceptors) contain?

A

Chemical receptors contain C fibres
Temperature and pressure receptors contain A-δ fibres and also C fibres
Touch receptors contain A-ß fibres and Proprioceptors (body position receptors) contain A-α fibres
(Slide 6)

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8
Q

What are nerve fibres also known as?

A

Axons
(Slide 6)

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9
Q

Order the 4 types of nerve fibres (axons) that are attached cutaneous and proprioceptors from fastest to slowest.

A

A-α
A-ß
A-δ
C
(Slide 6)

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10
Q

Are A-α,ß,δ and C fibres myelinated?

A

All types of A fibre are but C fibres are not
(Slide 6)

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11
Q

What are free nerve endings underneath the surface of the skin sensitive to?

A

Pain and temperature
(Slide 7)

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12
Q

How do P2X3 receptors contribute to a pain signal being formed?

A

Damaged / stressed cells release ATP which binds to P2X3 receptors on sensory neurons. This results in ion channels (including sodium ion channels) opening, resulting in an action potential
(Slide 8)

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13
Q

How do prostaglandin receptors result in increased pain reception?

A

Damaged / stressed cells releases prostaglandins which bind to prostaglandin receptors, which can enhance pain perception in order to reduce the risk of further injury
(Slide 8)

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14
Q

What skin temperature is considered to be noxious (harmful) cold?

A

<15 degrees
(Slide 10)

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15
Q

What skin temperature is considered to be noxious (harmful) heat?

A

> 45 degrees
(Slide 10)

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16
Q

What are cold and warm fibres activated by?

A

Changes in temperature
(Slide 10)

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17
Q

What 2 things are Pacinian corpuscles found under the surface of the skin sensitive to?

A

Pressure and vibration
(Slide 12)

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18
Q

What are Pacinian corpuscles composed of?

A

Connective tissue layers surrounding a nerve ending
(Slide 12)

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19
Q

What are Merkel’s disk, Ruffini’s ending and Messner’s corpuscle nerves found under the surface of the skin sensitive to?

A

Various types of touch
(Slide 13)

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20
Q

What 3 things happens due to physical stimulation of a Merkel cell (a part of Merkel’s disk)?

A

Serotonin (5-HT) release
Activation of 5HT3-R and 5HT2-R on A-ß fibres
Depolarisation and action potentials
(Slide 14)

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21
Q

What 2 things does a decreased number of Merkel cells due to old age lead to?

A

Decreased light touch sensing and an increased mechanical itch
(Slide 15)

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22
Q

What 2 things does a stronger stimuli lead to in sensory receptors?

A

An increased receptor and action potential (mV)
(Slide 16)

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23
Q

What are the 2 types of adaptation in sensory receptors?

A

Slowly and Rapidly adapting receptors
(Slide 17)

24
Q

What are 3 types of slowly adapting sensory receptors?

A

Pain, temperature and body position receptors
(Slide 17)

25
Q

What type of receptors are rapidly adapting sensory receptors?

A

Some mechanoreceptors
(Slide 17)

26
Q

What do slowly adapting receptors do?

A

They exhibit continual awareness and continue to respond constantly
(Slide 17)

27
Q

What do rapidly adapting sensory receptors do?

A

Ignore unimportant information and respond to only what is important
(Slide 17)

28
Q

What is a 1st order neuron?

A

The sensory neuron that directly detects a stimuli in the peripheral nervous system
(Stimuli > Spinal cord / brainstem)
(Slide 18)

29
Q

What is a 2nd order neuron?

A

An interneuron which receives input from the 1st order neuron and and transmits it to higher levels of the CNS
(Slide 18)

30
Q

What is a 3rd order neuron?

A

Another interneuron which receives input from the 2nd order neuron and carries it to the sensory cortex in the brain
(Slide 18)

31
Q

What is the midline?

A

A line which divides the body in half symmetrically
(Slide 19)

32
Q

What are the stages of the dorsal column system (DCS)?

A

Primary sensory neurons detect touch through their receptors on the skin, these primary sensory neurons then ascend through the dorsal column and dorsal column nuclei before synapsing in the medulla. The 2nd order neuron then crosses the midline and ascends through the medial lemniscus and into the thalamus where it synapses again. A 3rd order neuron then takes the information to the primary somatosensory cortex in the cerebal cortex
(Slide 19)

33
Q

What is the medial lemniscus?

A

A white matter pathway which ascends through the brainstem
(Slide 19)

34
Q

What 3 things does the dorsal column system (DCS) process?

A

Fine touch
Pressure
Proprioception (body balance)
(Slide 20)

35
Q

What is decussation and what does it lead to?

A

When a pathway crosses to the other side of the body (i.e. crosses the midline) resulting in sensory info being processed on the other side of the brain
(Slide 20)

36
Q

What are the stages of the spinothalamic system (STS)?

A

Primary sensory neurons detect pain and temperature change through their nociceptors or thermoreceptors in the skin. The axons of these 1st order neurons cross the midlineand then ascend through the lacteral spinothalamic tract, spinal cord and the medulla before synapsing in the thalamus where the axon of the 2nd order neuron goes to the primary somatosensory cortex (in the cerebal cortex)
(Slide 19)

37
Q

What 3 things does the spinothalamic system (STS) process?

A

Pain
Temperature
Some touch
(Slide 20)

38
Q

What part of the brain manages sensations which are to be consciously experienced?

A

The post central gyrus
(Slide 20)

39
Q

What type of pain do A-δ and C fibres manage?

A

A-δ fibres manage Sharp pain (first pain) where C fibres manage dull aching pain (second pain which occurs after time)
(Slide 22)

40
Q

What are 3 types of nociceptor?

A

Thermoreceptors
Mechanoreceptors
Polymodal receptors
(Slide 22)

41
Q

What are thermoreceptors activated by?

A

Extreme temperatures (>45 degrees or <15 degrees, due to cold fibres)
(Slide 22)

42
Q

What activates mechanoreceptors?

A

Intense pressure on the skin
(Slide 22)

43
Q

What activates polymodal receptors?

A

High intensity mechanical, chemical or thermal (both hot and cold) stimuli
(Slide 22)

44
Q

What is substance P?

A

A neuropeptide acts which acts as a neurotransmitter in the CNS and PNS. It is released from nociceptors in response to tissue damage or inflammation and then binds to its receptors on neurons in the spinal cord and brain where it enhanes the transmission of pain signals
(Slide 23)

45
Q

What is referred pain?

A

Where pain is felt in a location other than the actual site of injury or problem
(Slide 24)

46
Q

How can the spinal cord modulate pain carried by C fibres?

A

Via interneurons which release enkephalin on either descending stimuli from the CNS or localised serotonin, which activates pre and post-synaptic opiate receptors at spinal sensory synapse which eventually leads to decreased cAMP concentration, decreased PKA activity, and change in modulation of potassium ion conductivity, leading to decreased neuronal excitability and can reduce pain
(Slide 25)

47
Q

What is the spinal cord gate control theory of pain modulation?

A

It proposes that the spinal cord has a neuronal “gate” that can open or close to the passage of pain signals

Large fibres (A-ß fibres) that signal for touch / pressure can “close the gate” and activate the inhibitory function resulting in a weaker signal.

Small fibres (C fibres) that signal for pain can “open the gate” which results in a stronger pain signal
(Slide 26)

48
Q

What is the consequence of A-δ fibres synapsing in a different area of the spinal cord?

A

There are no interneurons that release enkephalins, and no opiate receptors resulting in morphine not being effective and therefore sharp pain being harder to treat
(Slide 27)

49
Q

What 3 factors can affect pain?

A

Previous experiences
Genetics
Mood
(Slide 28)

50
Q

What 4 ways does morphine help in treating pain?

A

It inhibits discharge of 1st order afferent neurons
Inhibits transmitter release of substance P preventing pain being transmitted
Hyperpolarises neurons, making it harder from them to reach the action potential threshold
Activates the spinal cord’s descending inhibitory control
(Slide 31)

51
Q

Can acute pain be benefitional?

A

Yes
(Slide 32)

52
Q

What can lead to persisting pain?

A

Chronic inflammation
(Slide 32)

53
Q

What receptors / channels are upregulated, which results in chronic inflammation?

A

Nav 1.8 and 1.9, TRPV1, P2X3, 4 and 7 are all upregulated
(Slide 32)

54
Q

What can lead to abnormal (neuropathic) pain?

A

Nerve or CNS damage
(Slide 32)

55
Q

What receptors / channels are upregulated and downregulated resulting in abnormal (neuropathic) pain?

A

Nav 1.3, TRPV1, P2X3, 4 and 7 are all upregulated whereas Nav 1.7 and 1.8 are downregulated
(Slide 32)

BM213: Introduction to Pharmacology (15 decks)

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