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Unit 11 > W1: Sensory pathways and pain physiology > Flashcards

W1: Sensory pathways and pain physiology Flashcards

1
Q

What is considered a somatosensation?

A

Proprioception
Vibration
Light touch

Gross touch
Pain
Temperature

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2
Q

What is the common architecture in all somatosensory pathways?

A

Consists of 3 order ascending neurons:
Sensory Neuron
Spinal cord/brain stem
Thalamus

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3
Q

What are the different types of somatosensory receptors?

A

Mechnoreceptor
Nociceptors
Thermoreceptors

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4
Q

What are the different types of mechanoreceptors and what are their functions?

A

Meissner Corpuscle - fine discriminative touch or tactile touch
Merkel Discs - pressure
Pacinian corpuscle - vibration
Muscle spindles - limb position

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5
Q

What are the different types of nociceptors and what is their function?

A

A-delta mechanical (encapsulated) - pin prick
C-polymodal (free nerve endings) - tissue damage.

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6
Q

What are the different types of thermoreceptors and what is their function?

A

Free nerve endings - cold or warmth

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7
Q

What does somatosensory mean?

A

A sensation that can occur anywhere in the body (rather than in a specific sense organ).
Associated with the primary sensory cortex.

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8
Q

What are the different somatosensory nerve fibres?

A

A-alpha
A-beta
A-dela
C

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9
Q

What are the properties of an A-alpha nerve fibre?

A

Somatosensory
Role in proprioception
Is myelinated
12-20micrometers in diameter
High conductivity at 75-120 m/s

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10
Q

What are the features of a A-Beta nerve fibre?

A

Somatosensory nerve fibre
Role in pressure and vibration
Myelinated
Conduction: 30-75m/s
Diameter: 6-12 micrometers

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11
Q

What are the features of an A-delta nerve fibre?

A

A somatosensory nerve fibre
Role in fast pain, cold.
is myelinated
5-30m/s conduction speed
1-6 micrometers in diameter

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12
Q

What are the features of a C-fibre?

A

Somatosensory nerve fibre
Role in slow pain, warmth
is NOT myelinated
Conduction of 0.5-2 m/s
Diameter of less than 1.5micrometers

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13
Q

Compare the conduction velocities of different somatosensory nerve fibres?

A

Fastest
A-alpha fibre
A-beta
A-delta
C fibres
Slowest

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14
Q

What is the difference between pain and nociception?

A

Pain - an unpleasant sensation (consicous interpretation) of something unpleasant that may or may not correlate with actual tissue damage

Nociception - neural/physiologal response to a noxious stimuli, can be subconscious.

Pain is possible without nociception

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15
Q

What are the four different processes in pain physiology?

A

Transduction
Transmission
Perception
Modulation

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16
Q

What is meant by the transduction of pain?

A

Noxious stumuli causes cell damage which releases sensitizing chemicals
These activate nociceptors and lead to the generation of an action potential.
Therefore - the transformation of noxious stimuli into electrical activity.

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17
Q

What does nociceptors are polymodal mean?

A

Can respond to many different stimuli
Such as:
Temperature extremes
Trauma
Hypoxia
Chemicals

18
Q

What are some of the different substances that can trigger an action potential in a nociceptor?

A

Prostaglandins
Bradykinins
Seratonin
Substance P
Histamine

19
Q

What are some mechanism that may cause pain transduction?

A

Stimulus activates:
- Mechanically gated Na and Ca ion channels
- heat sensitive ion channels
- mast cells to release 5HT/histamin
- damaged cells to release substances

20
Q

What are some of the substances released by damaged cells that can cause pain transduction?

A

Bradykinin: action on G-protein coupled receptors
ATP on ATP- sensitive K channels
Potassium
Prostaglandins

21
Q

What are some of the effects of pain transduction on blood vessels?

A

Blood vessel typically dilate to allow the inward migration of immune cells or growth factors.

22
Q

What is meant by pain transmission?

A

The conduction of electrical impulse through the nervous system.
Site of injury - spinal cord - brain stem - cerebrum.

23
Q

What is the pathway in pain transmission?

A

AP activates the afferent nerve fibre (1st order neuron) this has a cell body in the dorsal root ganglion projects into the dorsal horn of the spinal cord where it synapses and releases a pain neurotransmitter such as substance P.
This activates a 2nd order neuron. Desicates in the anterior white comissure to the contralateral side and travels up the spinal cord in the spinothalamic tract.
Synapses in the thalamus onto a third-order neuron which then projects up into the sensory cortex.

24
Q

What specific area in the dorsal horn are 1st order sensory neurons synapsing in?

A

May be called the substantia gelatinosa or the nucleus propius.

Specifically Laminae 1-5

25
Q

What is meant by the integrating centre in pain transmission?

A

The spinal cord
As receives afferent information, and can trigger multiple efferent pathways by interneurons

26
Q

What are the different efferent pathways that can be activated in the spinal cord in response to pain?

A

1 - efferent to brain/ascending tract - spinothalamic tract - role in memory and interpretation etc
2 - the reflex ark
Spilt into an excitatory internuron to a contracting muscle
And in inhibitory interneuron to a muscle you want to relax

27
Q

What is meant by pain perception?

A

The subjective sensation of pain

28
Q

What are the main two types of pain fibres?

A

A fibres - myelinated respons to mechanical pressure and produce sharp, localised and fast pain, further split into beta (pressure nd vibration) and delta (temperature)

C fibres - chronic, slow, dull or knawing pain, often delayed after the onset of injury

29
Q

What are the different regions of the brain that contribute to pain perception?

A

Thalamus/sesnory cortex - localisation
Limbic cortex - emotional experience
Reticular formation - alertness.
Autonomic interconnection

30
Q

What is meant by pain modulation?

A

The Process of altering the pain signals along the transmission pathway of pain.

31
Q

What are the different methods of pain modulation?

A

Gate theory
Descending Inhibitory Pathway
Cortical

32
Q

What is the Gate theory of pain modulation?

A

Pain signals can be interrupted in the substantial gelitanosa of the spinal cord
By this non-noxious stimuli can suppress noxious stimuli and decrease impulse transmission up the spinothalamic tract.

33
Q

By what mechanism can rubbing a wound alleviate pain?

A

Painful stimuli activates the alpha delta and c fibres, impulse travels along primary neuron to the dorsal horn
Deep touch is detected by pacinian corpuscle and projects along the DCML also into the dorsal horn via alpha beta neuron.
1. the impulse from deep touch activates an inhibitory internueron which inhibits the secondary neuron in the pain pathway so pain not transmitted (this is seen in substantia gelatinosa)
2. Neuron has an axonal branch that directly inhibts the synapse
Deep touch continues to travel up the the brain (no secondary neuron in the spinal cord)
Therefore only deep touch is perceived not pain
* note pain fibres may also modulate deep touch but normally to a lesser extend

34
Q

What is the mechanism of descending inhibitory pathway of pain modulation?

A

Periaqueductal gray - primary control centre for descending pain modulation
Descending pain inhibitory tracts originate here
Synapse in the nucleus raphe magnus (seratonin or enkephalin neurotransmister)
Neuron projects into..
Can act in the dorsal horn to inhibit the synapse between the primary and secondary neurons in the pain pathway
1: releases serotonin which activates enkephalin releasing neurons to inhibit the transmission to secondary neuron
2: Releases serotonin or norepinephrine to act directly on and inhibit the synapse.

35
Q

What are the different excitatory ubstances in neurotransmission of pain?

A

NT - glutamate
NP - Substance P

36
Q

What are the different inhibitory substances in the neurotransmission of pain?

A

NT - GABA, norepinephrine, 5HT
NP - enkephalins

37
Q

What anaglesics can be used to modify pain at the site of tissue injury?

A

Local anesthetics (wound infiltration field block)
NSAIDs/Cox-2 inhibitors
Opioid agonists

38
Q

What anaglesics can be used to stop peripheral nerve input?

A

Local anesthetics (peripheral nerve blocks)

39
Q

What anaglescis are effective at the spinal cord level?

A

These effect synapises between the primary and secondary neurons. Are neuromodulators
Includes:
Local anesthetics (epidural)
Opiods
Agonists
NMDA antagonists

40
Q

What anaglesics are effective in the cerebral cortex?

A

Opiod agonists
Acetominophen
ketamine

41
Q

What are some limitations of anaesthetics?

A

Local anaesthetics are very pH sensitive, with infection the pH may drop and the environment becomes acidic - this will prevent the local anaestethic from working.

42
Q

What is the cortical method of pain modulation?**

A

Changing the affective-motivational aspects of pain, so it looses its emotional and aversive components
By changing the way we think about pain we can reduce the feeling of pain.

Unit 11 (21 decks)

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