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NAB > Somatic sensation > Flashcards

Somatic sensation Flashcards

1
Q

Merkels cells

A

Slowly adapting type 1 afferents
Smallest receptive field so best for reading braille
close to epidermis
Has narrow linear dynamic range to encode magnitude with frequency

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2
Q

Meissner’s corpuscle

A

Rapidly adapting type 1 afferent
Responds best to low frequency vibration; slip between object
Close to epidermis
Glabrous skin

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3
Q

Pacinian corpuscle

A

Rapidly adapting type 2 afferent
Responds best to high freq (300Hz) vibration
Deeper in dermis

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4
Q

Ruffini endings

A

Slowly adapting type 2 afferents
Deeper in skin
Respond to skin stretch; good for hand position and object motion perception

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5
Q

Accessory structure

A

Structure not directly involved in the transduction of a stimulus but that plays a role in conduction or analysis e/g lamellae of Pacinian corpuscle; confers property of being rapidly adapting

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6
Q

Phase locking

A

Nerve always fires at same part of the AP

Allows additional recruitment to encode magnitude of a stimulus rather than frequency of discharge

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7
Q

Free nerve endings

A

Primarily respond to temperature and nociceptive stimuli

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8
Q

Paradoxical cold

A

A heat stimulus on a cold spot will feel cold due to labelled line code and lack of comparison with other receptors because this is a discrete stimulus

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9
Q

C tactile afferents

A

Longer lasting response to brushing of skin

Correlates with pleasantness of the stimulus

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10
Q

ABeta fibres

A

Largest, shortest latency
Carry mechanoreception; proprioception and touch
First affected by hypoxia, last by anaesthetic

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11
Q

Adelta fibres

A

Responsible for sharp stabbing pain

Medium

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12
Q

C fibres

A

Unmyelinated, smallest
Responsible for warm burning pain/itching pain
First affected by anaesthetic and last by hypoxia

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13
Q

Anterolateral system/spinothalamic tract

A

Major ascending nociceptive pathway
Axons from neurons in layers 1,5,6,7
Ascending in contralateral, anterolateral white matter
Crosses midline straight after leaving dorsal horn

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14
Q

Dorsal column/medial lemniscal system

A

Mainly AAlpha and ABeta
Fibres reach the DCN (gracile for lower limb, cuneate for upper)
Then cross midline and travel contra laterally to thalamus via medial meniscal tract

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15
Q

Brown sequard syndrome

A

Hemisection through spinal column

  • Ipsilateral loss of tactile and limb position sense
  • Contralateral loss of pain/temp
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16
Q

Syringomyela

A

Loss of middle of spinal cord so Adelta and C are selectively abolished
Bilateral loss of pain and temp

17
Q

Posterior column syndrome

A

Dorsal aspect of spinal cord carrying Abeta fibres means bilateral loss of limb position and tactile sense

18
Q

Role of lateral inhibition

A

Receptive fields have excitatory and inhibitory regions
Stimulating OFF surround can turn off the output from the excitatory centre

Good for sharpening two point discrimination

19
Q

Cells in posterior part of ventromedial nucleus

A

From lamina 1

Neurons here respond best to noxious heat stimuli above 43 degrees

20
Q

Somatosensory cortex

A

Primary input is layer 4
Layers 5/6 do descending info to BG, SC, brainstem
Layers 2/3 to other parts of cortex

21
Q

Homunculus

A

Map of the somatosensory inputs to the cortex

22
Q

Area 2 of somatosensory cortex

A

Directional sensitivity
Via 3 sets of 2 receptive fields where one is excitatory and one is inhibitory
Responds best to stimulus moving through excitatory region first and then inhibitory

23
Q

What areas are active during active touch

A

Primary somatosensory cortex (this is only one active in passive touch)
Primary motor cortex
ACC (anterior cingulate cortex)

24
Q

Role of context

A

Attention enhances responses of enurons

Memory also plays a role e.g bigger output if this stimulus is larger than previous one

25
Q

Cortical remapping

A

After limb lost, the area on the cortex that represents that body part is taken over by the neighbouring area
So touching another area gives sensation in amputated limb

26
Q

Pain

A

Unpleasant sensory and emotional experience associated with actual or potential tissue damage

27
Q

Dorsal horn lamina with wide dynamic range neurons

A

Lamina 5

Also has input from Abeta, Adelta, C

28
Q

Referred pain

A

Pain perceived at a distance from affected organ due to visceral-somatic convergence on second order neurons

29
Q

Cortical representations of pain

A

Primary somatosensory cortex
ACC
Insula (homeostasis)

30
Q

Gate control theory of pain

A

Input from Abeta fibres can active inhibitory interneurons to inhibit transmission cell in lamina 5 to decrease pain felt

31
Q

Areas for descending control of pain

A

Periaqueductal gray in midbrain (has map within it for applying to endogenous opioid system to areas)
Raphe Magnus nuclei in the rostral medulla
Nucleus paragigantocellularis in rostral medulla

32
Q

Sensitising agents that don’t directly excite the nociceptor

A

PGE2

Nerve growth factor

33
Q

Allodynia

A

Previously painless stimuli now painful

34
Q

Hyperalgesia

A

Previously painful stimuli now more painful

35
Q

How does PGE2 act to sensitise the nerve

A

Acts via EP4 receptors which are Gs coupled so get increase in adenylyl cyclase activity, more cAMP, more PKA, phsophrylates Nav channels to decrease threshold

36
Q

Neuropathic pain

A

When peripheral nerve damage leads to pain that outlasts the injury itself

37
Q

Neurogenic inflammation

A

Nociceptive nerve terminals release substance P and CGRP when stimulated causing vasodilation and increased permeability

38
Q

Mui opioid receptor

A

Gi coupled
Betagamma subunit activates GIRK channels to cause K+ exit and hyper polarisation (presynaptically this inhibits neurotransmitter release)

Decreased cAMP so less PKA, counteracting effects of PGE2 on Nav channels

39
Q

Treating neuropathic pain

A

Analgesics: NSAIDs, opioids
Antidepressants: serotonin-NA-reuptake inhibitor (NA is involved in descending modulation of pain)
Gabapentin: decreases Cav expression
NaV blockers like lidocaine

NAB (8 decks)

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