Spinal Circuits for Touch, Pain, and Itch Flashcards
What are mechanoreceptors?
Sensory nerve endings depolarised by mechanical force of skin
What are the 5 types of mechanoreceptors?
Merkel cells Meissner corpuscles Pacinian corpuscles Ruffini endings Free nerve endings
What do Merkel cells detect and are they superficial/deep?
Light pressure
Superficial
What do Meissner corpuscles detect and are they superficial/deep?
Light vibration
Superficial
What do Pacinian corpuscles detect and are they superficial/deep?
Strong vibration
Deep
What do Ruffini endings detect and are they superficial/deep?
Stretch
Deep
What do free nerve endings detect?
Nociception (nociceptors)
Itch (pruritoceptors)
What do low-threshold MS transduction molecule-expressing neurons detect?
Innocuous mechanical
What do TRPA1 transduction molecule-expressing neurons detect?
Nociception, pruritoception
What do TRPV1 transduction molecule-expressing neurons detect?
Nociception, pruritoception, capsaicin
What do TRPV3 transduction molecule-expressing neurons detect?
Warm
What do TRPM8 molecule-expressing neurons detect?
Cold, menthol
What are the characteristics of Abeta fibres and what do they detect?
Thick myelination
Fast conduction
Innocuous touch
What are the characteristics of Adelta fibres and what do they detect?
Thin myelination
Slow conduction
Sharp pinprick pain
What are the characteristics of C fibres and what do they detect?
Unmyelinated
Very slow conduction
Long-lasting burning pain
What do Ia and Ib afferents detect?
Proprioception
From superficial to deep, in which order do the sensory afferents terminate in the spinal cord?
C fibres
A fibres
Ia and Ib afferents
How does injury/stimulation affect dorsal spinal cord neuron receptive fields?
Changes size
Which laminae do projection neurons to brain originate from?
I and IV/V
Name the 4 methods of sensory afferent input processing by dorsal horn circuitry
Spatial convergence
Modality convergence
Selective amplification
Selective inhibition
Name the 3 theories of interneuron central processing
Intensity theory
Specificity theory
Combinatorial code theory
Describe intensity theory
Convergence of multiple afferents onto interneuron
Need certain intensity of any stimulus to interpret
If 2 modalities input to same interneuron simultaneously highest intensity modality perceived
Describe specificity theory
One afferent synapses onto interneuron with corresponding modality
Describe combinatorial coding theory
One afferent synapses onto interneuron with corresponding modality
Afferent also activates other afferents and their interneurons
Interaction and opponency between pathways carrying signals
Sensation depends on combined activation of pathways
What does Melzack and Wall’s gate theory of pain suggest?
Touch input allows inhibition of pain transmission
Convergence of 2 modalities
