Chemical anatomy of pain (2)

Question 1

What is the role of the ACC (Anterior Cingulate Cortex) in pain processing?

Answer 1

ACC Involved in emotions and attention related to pain

Question 2

What is the role of the primary sensory cortex in pain processing?

Answer 2

Responsible for sensory discrimination of pain

Question 3

What is the role of the prefrontal cortex in pain processing?

Answer 3

Plays a role in the cognitive aspects of pain processing

Question 4

What is the role of the insula in pain processing?

Answer 4

Integrates sensory and motor information related to pain

Question 5

What is the role of the amygdala in pain processing?

Answer 5

Influences emotional affect associated with pain

Question 6

What is the role of the spinal cord in pain processing?

Answer 6

• In dorsal horn, it processes sensory input, while in the ventral horn, it’s responsible for motor output
• the grey matter is divided into 10 laminae - with different functions, including pain and touch processing

Question 7

How is pain processing organized in the spinal cord’s grey matter?

Answer 7

• spinal cord’s grey matter consists of 10 laminae
• Pain signals, carried by A-delta & C-fiber nociceptors, are processed in specific laminae
• this segregation allows for the differentiation of pain & touch signals in spinal cord

Question 8

What are peripheral cutaneous afferents?

Answer 8

• sensory nerve fibers that transmit info from the skin to CNS, contributing to the perception of touch, pressure, temperature, & pain

Question 9

What are the peripheral cutaneous afferents associated with mechanosensation?

Answer 9

Merkel cells: Associated with the sense of light touch and the discrimination of shapes and textures.
Ruffini ending: Function as slowly adapting mechanoreceptors.
Meissner’s corpuscle: Mechanoreceptors that are sensitive to light touch and rapidly adaptive

Question 10

What is the first step leading to the perception of innocuous touch in the somatosensory system?

Answer 10

• the activation of cutaneous sensory neurons known as LTMRs (Low-Threshold Mechanoreceptors)

Question 11

How are cutaneous sensory neurons classified?

Answer 11

Cutaneous sensory neurons are classified as Ab (A-beta), Ad (A-delta), or C based on:
Cell body size
Axon diameter
Degree of myelination
Axonal conduction

Question 12

What distinguishes LTMRs (Low-Threshold Mechanoreceptors)?

Answer 12

-LTMRs are distinguished by their activation by weak innocuous mechanical force applied to skin.
- they’re associated with specific cutaneous end organs
- LTMRs have preferred stimuli or tuning properties

Question 13

What are the major types of mechanosensory end organs found in glabrous skin?

note: Glabrous skin = thick skin found over the palms, soles of the feet and flexor surfaces of the fingers that is free from hair

Answer 13

• Glabrous skin contains four types of mechanosensory end organs:
• Pacinian corpuscles (Pacinian c)
• Ruffini endings
• Meissner’s corpuscles (Meissner c)
• Merkel cells

Question 14

What are slowly adapting receptors (SA receptors), and how are they classified?

Answer 14

• Slowly adapting receptors = mechanoreceptors that maintain firing during sustained indentation
• further classified into SAi and SAii types based on their specific properties. (Abraira & Ginty, 2013)

Question 15

What happens in the spinal cord dorsal horn regarding LTMRs?

Answer 15

• the spinal cord dorsal horn receives axonal projections & terminations from every LTMR that innervates the skin.
• this convergence occurs in a somatotopic & columnar manner, and likely to be a key location for LTMR integration & processing of info (Abraira & Ginty, 2013)

Question 16

Where do A-fiber axons ascend in the spinal cord, and what is their role?

Answer 16

• A-fiber axons ascend to the dorsal column nuclei and make contacts within the spinal cord
• their role includes carrying discriminative touch info & projecting into the cord to activate various dorsal horn interneurons

Question 17

where do C fibers run?

Answer 17

C fibers run in Lissauer’s tract

Question 18

How do innocuous and noxious inputs distribute in the spinal cord, and what are their patterns?

Answer 18

• Innocuous and noxious inputs exhibit distinct but overlapping distribution patterns in the spinal cord

Question 19

How do low-threshold afferents contribute to sensory processing in the spinal cord?

Answer 19

• Low-threshold afferents project into the dorsal columns medial lemniscus system (which carries discriminative touch info)
• they also project into the spinal cord and activate a range of dorsal horn interneurons

Question 20

What is the primary function of Laminae I in the spinal cord?

Answer 20

• associated with nociception & contains nociceptive-specific cells (primarily respond to noxious or painful stimuli)
• plays a role in processing pain-related information & has small receptive fields

Question 21

What types of stimuli do wide dynamic range cells in Laminae V-VL respond to?

Answer 21

• wide dynamic range cells in Laminae V-VL can respond to a broad range of sensory stimuli (incl. noxious & innocuous inputs)
• have small to large receptive fields & receive input from C and Ad fibers.

Question 22

What is the main function of Laminae VIII-X in the spinal cord?

Answer 22

• Laminae VIII-X associated with visceral nociception & contain nociceptive-specific cells
• Neurons in these layers typically have large/bilateral receptive fields & play a role in processing information related to visceral pain

Question 23

What is the role of Lamina I & V(X) projection neurons in the spinal cord?

Answer 23

• carry nociceptive information from the spinal cord to the brain
• they transmit info related to pain & noxious stimuli to higher brain centers for further processing

Question 24

How do visceral and muscle pain signals differ in terms of localization in the spinal cord?

Answer 24

• Visceral & muscle pain signals involve sparse C fibers in the cord, leading to poorly localized sensations
• these signals can also converge with cutaneous input, resulting in referred pain

Question 25

What is referred pain?

Answer 25

• pain perceived at a location different from the actual site of the painful stimulus
• often occurs when visceral & muscle pain signals converge with cutaneous input

Question 26

What is the nature of all projection neurons in the spinal cord, specifically in relation to neurotransmitters?

Answer 26

• All projection neurons in the spinal cord are thought to be excitatory, and none of them express GABA/glycine

Question 27

What percentage of projection neurons express the substance P receptor NK1, particularly in rodents?

Answer 27

Around 80% of projection neurons express the substance P receptor NK1, at least in rodents

Question 28

What is the significance of parallel ascending pathways in the anterolateral spinal system?

Answer 28

Parallel ascending pathways in the anterolateral spinal system are functionally different

Question 29

What is the role of RVM neurons projecting onto spinal enkephalinergic neurons in nociception?

Answer 29

RVM neurons projecting onto spinal enkephalinergic neurons are GABAergic but facilitate nociception

Question 30

Why is the dorsal horn of the spinal cord important?

Answer 30

crucial for:
- processing noxious inputs, integrating peripheral stimuli
- receiving descending signals from brain
It is modality-specific