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NEURO > Sensory Systems (Including physiology of pain) > Flashcards

Sensory Systems (Including physiology of pain) Flashcards

1
Q

Examples of sensory receptors with free nerve endings? Examples of ones with complex structure?

A
  • Free endings: nociceptors, cold receptors
  • Complex: Pacininan corpuscle (sensitivity to vibration and pressure), Meissner’s corpuscle (sensitivity to light touch)
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2
Q

Describe the signal transduction pathway starting at a sensory receptor

A
  • Sensory receptor transduces stimulus to a graded potential
  • If graded potential is large enough, triggers AP at axon
  • Long distance transmission then occurs via several nerves
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3
Q

How do sensory receptors encode the intensity of a stimulus?

A

Frequency of APs generated by a sensory receptor encodes the intensity of a stimulus

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4
Q

What determines the acuity of sensation at different points on the body?

A

The density of innervation and size of receptive fields

less neurons and bigger fields = lower acuity

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5
Q

What types of neurons carry cutaneous touch, pressure and vibration information? Describe the neuron structure?

A

A(beta) fibres

  • large myelinated, (30-70m/s)
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6
Q

What types of neurons carry cutaneous cold, fast pain and pressure information?

A

A(delta) fibres

  • Small myelinated (5-30m/s)
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7
Q

What types of neurons carry cutaneous warmth and slow pain information?

A

C fibres

  • Unmyelinated (.5-2m/s)
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8
Q

What types of neurons carry proprioceptive information?

A

A(alpha) and A(beta) fibres

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9
Q

What type of fibres make up the lateral spinothalamic tract?

A
  • Thermoceptive and nociceptive

- A(delta) and C fibres

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10
Q

What type of fibres make up the dorsal column tract?

A
  • Mechanoreceptive fibres

- A(alpha) and A(beta) fibres

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11
Q

What sensory information is lost when damage to the dorsal column of the SC occurs?

A

Mechanoreceptive information from below the lesion on the ipsilateral side

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12
Q

What sensory information is lost when damage to the lateral spinothalamic tract of the SC occurs?

A

Nociceptive and thermoceptive info from below the lesion on the contralateral side

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13
Q

What is the difference between rapidly adapting and slowly adapting neurons?

A
  • Rapidly adapting: fires a few APs in response to the stimulus, then adapts to the stimulus and stops firing, only fires again when stimulus is removed
  • Slowly adapting: Fires APs at a high rate when stimulus starts, then at a low rate for the duration of the stimulus, stops firing when stimulus is removed
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14
Q

What is convergence?

A

Where you have lots of neurones synapsing onto one neuron

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15
Q

Advantages and disadvantages of convergence?

A
  • Pros: saves of number of neurones needed

- Cons: reduced acuity

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16
Q

What is referred pain?

A

Feeling pain at a site other than the site of origin

Can be due to convergence of neurones from different places onto the same neuron on its way up to the brain (eg. MI felt in chest and arm)

17
Q

What is lateral inhibition?

A
  • Neuron with the receptive field closest to the stimulus inhibits its neighbours with closely associated receptive fields
  • Increases acuity
18
Q

Difference between sensation and perception?

A

Perception is the limited amount of what you sense that you actually notice

19
Q

Different types of pain?

A
  • Sharp/stabbing vs. diffuse, throbbing
  • Fast (initial) vs slow (delayed)
  • Acute vs. chronic
  • Visceral pain (hard to localize)
  • Referred pain
  • Phantom pain
20
Q

How is signal transduction initiated in nociceptors?

A
  • low pH and heat cause protein channels to open and initiate an AP
  • Chemical mediators from damaged tissue cause G-protein coupled receptor cascades that open protein channels
21
Q

Examples of protein channels involved in initiation of signal transduction in nociceptors?

A
  • ASIC (acid/low pH)

- TRPV1 (heat)

22
Q

Examples of chemical mediators that initiate signal transduction in nociceptors via G-protein cascade?

A
  • Bradykinin
  • Prostaglandins
  • Histamine
23
Q

How does activation of mechanoreceptive neurons in the same area as an injury inhibit pain being felt? (Segmental gate control theory)

A

Mechanoreceptive fibres in the dorsal column can activate inhibitory interneurons that inhibit presynaptic fibres in the dorsal root (before lateral spinothalamic tract)

  • Why rubbing something better works, mechano feedback causes inhibition of nociceptive feedback (closes the gate)
24
Q

How do nucleii in the peri-aqueductal grey matter inhibit nociception?

A
  • Via the descending control mechanism: nuclei in the PAG activate nuclei in the nucleus raphe magnus (NRM) which travel down the SC to the level where pain is occurring.
  • They then activate the same inhibitory interneurones as the mechano receptors do, and close the gate
25
Q

When is the descending control mechanism used?

A
  • Eg. in battle injuries

Where you are injured but need to be focused on a task so the brain inhibits this feeling of pain

26
Q

Two main classes of analgesics?

A
  • NSAIDs

- Opiates

27
Q

How do prostaglandins facilitate nociception?

A

They hyper-sensitize receptors that respond to bradykinin, which should then initiate signal transduction when exposed to the same levels of bradykinin

28
Q

How do NSAIDs inhibit pain?

A
  • Inhibit cyclo-oxygenase which coverts arachidonic acid to prostaglandins
  • Therefore by stopping prostaglandins from being made
  • Especially effective against pain from inflammation, which relies heavily on prostaglandin mediated signal transdiction
29
Q

How do local anaesthetics stop pain?

A
  • By blocking Na action potentials, and therefore all axonal transmission
  • Don’t only numb pain, stop the mechanoreceptive sensation as well
30
Q

How does trans-cutaneous electric nerve stimulation (TENS) inhibit pain?

A
  • Mechanoreceptive fibres are easier to activate via electrical stimulation on the skin that nociceptive fibres
  • Therefore, by electrically activating mechano fibres in an area you inhibit pain via the segmental gate control mechanism
31
Q

How do opiates inhibit pain?

A
  1. They activate G-protein coupled receptors that open K channels, hyper-polarizing neurones and therefore reducing their sensitivity to graded potentials
  2. Inhibit transmitter release in the dorsal horn (close the gate - activate same receptors as inhibitory interneurones)
  3. Activate descending control mechanism by activating nucei in the peri-aqueductal grey matter
32
Q

What is most likely the reason opiates are such effective pain relievers?

A

Because they inhibit pain via 3 different mechanisms

NEURO (52 decks)

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